Growing Mouth Bacteria in a bowl of sugar water

Growing Mouth Bacteria in a bowl of sugar water

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I want to teach my nephew why brushing in necessary and how sugar in mouth reduced by bacteria to acid.

I plan to put sugar mixed water in bowl and take swab from his mouth and dip in bowl, and test ph using Litmus paper to show him that sugar is converted to acid.

Is it possible to grow mouth acid making bacteria in this solution and will it change pH enough to show in litmus paper?

I like the concept of this demonstration for teaching science!

As rotaredom's comment pointed out, bacteria does not grow in plain water with sugar. Bacteria require a nitrogen source, trace minerals and vitamins to grow in significant numbers.

I have a few recommendations that you can try, but I attached an extensive guide to kitchen microbiology below.

  1. Growing the microbes in diluted milk (~ 1:10 dilution) + salt (a pinch for half glass) with and without added sugar (1 teaspoon for half a glass) might be a good starting point. Add yeast extract if you have some (not bakers yeast, but this is the killed version of that).

  2. Make sure to boil and cool the milk, the container and other ingredients to keep conditions sterile.

  3. Avoid a cotton swab if you can (as the cotton might not be sterile), I would take some milk solution, swirl it in my mouth and spit it back into the same container.

  4. Also have a sterile culture in the experiment, without the oral microbes for comparison and a great teaching point.

  5. Grow the microbes for 2-4 days with an air permeable cap (the air allows faster growing aerobic organisms, the cap ensures dust does not fall in)

    Extensive source: Microbiology at Home: A short non-laboratory manual for enthusiasts and bioartists PS: I'm studying PhD to be a microbiologist

Oral Bacteria: What Lives In Your Mouth?

While you can’t see or taste them, your mouth is home to colonies of microbes, including germs like fungus and bacteria. While most of these tiny oral bacteria are harmless—and even helpful—others can lead to tooth decay and gum disease. Luckily, with good oral care practices and a healthy diet, you should be able to manage the bacteria in your mouth from causing any serious issues.

According to the National Institutes of Health, your mouth is home to 700 species of microorganisms or bacteria that live on your teeth, tongue, and even the pockets between your tooth and gum. While the good microbes help your mouth manage bad microbes' growth and protect against the harmful bacteria in food, the bad microbes form communities with other germs and can form plaque and acid. That’s because these bacteria are living, growing, eating, and reproducing.

These bacteria feed on the sugars in the food and drinks we consume and leave behind waste or plaque. And the bacteria that are attracted to sugar turn it into acid, which can lead to decay on the surface of your teeth and lead to plaque development.

1. Homemade extraction of your own DNA

Ingredients: transparent glass, salt, liquid soap, grapefruit juice, and alcohol (e.g. disinfectant, rum, vodka, etc.).

The first step consists of spitting on the glass and adding a pinch of salt to it. Then, add some liquid soap (like the one you use for washing the dishes), juice from a grapefruit, and some drops of alcohol. Once you have everything on the glass, stir the mixture, et voilà.

The white mucous filaments you observe on top of the mixture is your DNA.

The saliva contains cells from your mouth that have DNA inside them. The detergent is used to break down the membranes that protect the DNA, and releases it into the recipient. The salt makes the DNA denature* and precipitate, while the grapefruit juice neutralizes the proteins that could damage the DNA.

2) Where do the attacking acids come from?

The acids that cause tooth demineralization tend to be produced by specific types of bacteria, with two of the most prominent types (at least according to historic studies) being streptococci mutans and lactobacilli .

The primary home of these damaging bacteria is within dental plaque:

  • S. mutans plays an instrumental role in the initiation of cavity formation due to its ability to adhere to and subsequently colonize tooth surfaces.
  • As lesion formation progresses, conditions frequently shift to ones especially favorable for lactobacilli colonization. And over time, this strain often plays an ever-increasing role in the decay process.
  • But with any one cavity, it’s expected that many more types of bacteria will have played a role too. With their level of presence, or even absence, fluctuating according to the current stage and specific characteristics of the ongoing lesion.
A) The acids that cause decay are bacterial waste products.

The bacteria that cause cavities are living organisms. And just like all living things, they consume food and in return create waste products.

As it happens, the wastes that these types of bacteria create are very acidic (having a pH of 4 and lower). The primary compound they produce, and the one primarily responsible for tooth demineralization, is lactic acid .

B) What kind of food is involved?
C) How quickly does the acid form?

Research by Stephan published in 1944 included a graph that illustrated the pattern of acidic response that takes place in a person’s mouth immediately after their rinsing with a sucrose (table sugar) solution.

The Stephan Curve shows what happens after you eat a sugary treat.

When sugar consumption causes a pH drop of 5.5 or below, decay formation can take place.

  • From the moment of exposure, oral conditions immediately become increasingly acidic. A maximum value is ultimately reached in approximately 5 to 20 minutes .
  • After this point, a gradual recovery, taking between 30 to 60 minutes, begins that eventually returns the mouth to its original (pre-rinse) status.

Each of the factors listed below will influence how intense the attack will be (how quickly and how much acid is produced), and therefore how long the pH of the mouth will remain below 5.5 (the level where demineralization will occur).

  • The type and number of bacteria living in dental plaque. (Streptococcus mutans is the type of bacteria most associated with lactic acid formation and therefore cavity development.)
  • The density of the plaque. Thicker plaque helps to protect bacteria and the acids they produce (see diagram below).
  • The type of sugary meal consumed. Complex starches must be broken down into their component sugars before bacteria can digest them. In comparison, sucrose can be metabolized straight away.

Fact – Within minutes of receiving a sugary meal, oral bacteria start to produce the acids that cause tooth decay.

Cavity prevention suggestion :

The less sugar you consume, or the fewer number of times you eat sugary foods, or the less time you allow sugars to remain in your mouth, the less exposure your teeth will have to bacterial acids. Toward this goal:

  • Use artificial sweeteners rather than natural sugars.
  • Don’t linger when snacking on or sipping sugary foods and beverages. Consume these items fairly quickly and be done with them.
  • Minimize how long sugars are allowed to remain in your mouth. Brush and floss, or at least rinse, promptly after consuming foods.
  • Substitute xylitol for table sugar. This natural alternative helps to prevent cavities by having an effect on the types of bacteria that create it.
  • Keep the level of plaque in your mouth to a minimum. The more cavity-causing bacteria that are present, the greater the amount of lactic acid that’s produced.

Growing Yeast: Sugar Fermentation

Yeast is most commonly used in the kitchen to make dough rise. Have you ever watched pizza crust or a loaf of bread swell in the oven? Yeast makes the dough expand. But what is yeast exactly and how does it work? Yeast strains are actually made up of living eukaryotic microbes, meaning that they contain cells with nuclei. Being classified as fungi (the same kingdom as mushrooms), yeast is more closely related to you than plants! In this experiment we will be watching yeast come to life as it breaks down sugar, also known as sucrose, through a process called fermentation. Let&rsquos explore how this happens and why!


What is sugar&rsquos effect on yeast?


  • 3 Clear glass cups
  • 2 Teaspoons sugar
  • Water (warm and cold)
  • 3 Small dishes
  • Permanent marker


  1. Fill all three dishes with about 2 inches of cold water
  2. Place your clear glasses in each dish and label them 1, 2, and 3.
  3. In glass 1, mix one teaspoon of yeast, ¼ cup of warm water, and 2 teaspoons of sugar.
  4. In glass 2, mix one teaspoon of yeast with ¼ cup of warm water.
  5. In glass 3, place one teaspoon of yeast in the glass.
  6. Observe each cups reaction. Why do you think the reactions in each glass differed from one another? Try using more of your senses to evaluate your three glasses sight, touch, hearing and smell especially!


The warm water and sugar in glass 1 caused foaming due to fermentation.

Fermentation is a chemical process of breaking down a particular substance by bacteria, microorganisms, or in this case, yeast. The yeast in glass 1 was activated by adding warm water and sugar. The foaming results from the yeast eating the sucrose. Did glass 1 smell different? Typically, the sugar fermentation process gives off heat and/or gas as a waste product. In this experiment glass 1 gave off carbon dioxide as its waste.

Yeast microbes react different in varying environments. Had you tried to mix yeast with sugar and cold water, you would not have had the same results. The environment matters, and if the water were too hot, it would kill the yeast microorganisms. The yeast alone does not react until sugar and warm water are added and mixed to create the fermentation process. To further investigate how carbon dioxide works in this process, you can mix yeast, warm water and sugar in a bottle while attaching a balloon to the open mouth. The balloon will expand as the gas from the yeast fermentation rises.

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Identification of Bacterial Growth: 3 Mediums

1. Observe and record the morphology of colony and pigment production in nutrient agar plate or tube. To identify a bacteria by its colonial morpho­logy only, may not be enough. So a battery of other relevant tests is to be undertaken.

However, pigment production, if present, may give some clue. Generally, bacterial growth with green pigment on nutrient agar is supplied. Pigment is diffusible in the medium in case of pigmented Pseudomonas (Fig. 7.2) whereas Staphylococcal pig­ment remains localised within the bacterial colony (Fig. 7.1), e.g. golden-yellow pigment in Staph, aureus and white pigment in Staph, epidermidis.

In liquid medium like peptone water, greenish pigment may also be present with surface pellicle formation. Surface pellicle (e.g. in cases of vibrio and Bacillus) indicates strong aerobic nature of bacteria as more oxygen is available near surface.

2. Examine Gram’s stained smear and hanging drop preparation.

(b)Gram-positive cocci in clusters (Staphylococci)

(c) Gram-positive rods with or without spore

The findings are recorded and Tables 7.3, B, C, G & H are followed to arrive at identity.

Growth on Any Other Special (Selective/Inhibitory/Indicator) Medium:

Any growth on special selective/indicator/ inhibitory medium is to be identified by undertaking the following steps:

1. Identify the medium and think the bacteria which grows on it.

2. Note the colony character and any indicator of growth for any special genus, e.g., sucrose fermenting flat yellow colony on T.C.B.S. agar indicates growth of vibrio.

3. Perform morphological study by gram stain or any special stain (eg. capsule staining, spore staining, Wayson’s staining for Y. pestis etc.).

6. Go for biochemical tests.

7. Tests for enzyme and toxin production.

8. Antigen detection by slide agglutination or capsule swelling using specific high titre sera (HTS).

A. Pseudomonas Aeruginosa:

The organisms produce blue pus and pyocyanea literally means “blue pus”. Ps. aeruginosa is an impo­rtant cause of hospital-acquired infection. Most infections occur in patients with serious underlying diseases like burns and malignancy or as a result of therapeutic procedures (catheterisation, cystoscopy). Prior treatment with antimicrobials favour pseudo­monas infection.

1. Skin infections especially in wound, pressure sores and burns.

2. Urinary infection, usually following catheteri­sation or in chronic infections.

3. Respiratory infections, especially in immuno­suppression and cystic fibrosis.

4. Ear infections, e.g. chronic otitis media and otitis externa.

5. Eye infections, usually hospital acquired.

6. Septicaemia may develop in neonates and old debilitated persons, particularly in patients receiving cytotoxic drug or irradiation.

7. Acute necrotising vasculitis which leads to haemorrhagic infarction of skin (ecthymagangrenosa) and of internal organs (liver and kidney).

Laboratory diagnosis:

Pus, wound swab, mid-stream speci­men of urine, CSF, sputum or blood.

On MacConkey’s agar they show pale, flat colonies with a spreading border. In nutrient agar or Mueller-Hinton agar there is diffuse bluish, greenish or reddish brown pigments, and a grape­like or fruit-like odour. Selective media such as cetrimide agar is useful for isolation of the organism from faeces or other samples contaminated with mixed flora.

Identification is made based on:

1. Characteristic colony morphology and gram- film appearance.

2. Grape-like or fruit-like odour of the colony.

3. Mucoid colony variants are particularly pre­valent in respiratory tract specimens.

4. Biochemically, P. aeruginosa is confidently identified based on the following features:

(a) Positive oxidase test (Table 7.10).

(b) Triple sugar iron (TSI) agar reaction of alkaline over no change.

(c) Bright green diffusible pigments on Mueller-Hinton or other non-dye-containing agars (e.g. N. agar).

Occasional strains of P. aeruginosa produce only pyoverdin, which would not differentiate them from P. fluorescens or P. putida. These latter species fail to grow at 42°C, while P. aeruginosa grows at 42°C.

B. Staphylococcus (S.aureus):

S. aureus is an important pyogenic organism and Box 1 shows the important diseases produced by the same.

Laboratory diagnosis:

These are to be collected depending on the nature of lesion, pus from suppurative lesions, CSF from meningitis, blood from septicaemia, sputum from respiratory infection and suspected food, vomit or faeces from food poisoning.

Examination of a Gram-stained smear of pus and other specimens shows Gram-positive cocci in clusters with some single and paired cocci.

(a) Specimens are inoculated on blood agar or selective agar medium with 7% sodium chloride which inhibits the growth of most organi­sms other than staphylococci.

(b) Mannitol salt agar is selective and differential media for staphylococci. Mannitol is fermented by S. aureus but not most other staphylococci.

(a) Coagulase test: S. aureus is coagulase positive.

(b) Antibiotic susceptibility tests, biochemical profiles (bio-typing), phage typing, nucleic acid analysis may be done for the intra-species identifica­tion of the organism for epidemiological study to trace the source of staphylococcal infections.

C. Bacillus:

Members of the genus Bacillus are aerobic, spore- bearing, gram-positive bacilli arranged in chain. The spores are retractile, oval and central in position and its diameter is the same as the width of the bacteria.

Bacillus anthracis:

(a) B. anthracis — causative agent of anthrax.

(b) B. cereus — cause food poisoning.

II. Non-pathogenic (saprophytes):

(1) Large-celled: B. megaterium, B. cereus

(2) Small-celled: B. subtilis, B. stearothermophilus

Anthrax is a zoonosis, humans are occasionally secondarily infected from diseased animal or animal products.

Anthrax is of 4 clinical types:

Spores enter the skin most commonly through abraded skin, crusts or hair follicles and usually produce a single painless blister, often called ‘malignant pustule’.

Ingestion of contaminated meat results in severe and often fatal form of gastroenteritis which is far less common than cutaneous form.

It is often referred to as ‘wool-sorter’s disease’ and is caused by inhalation of large number of spores and is usually fatal. It is a rare form of anthrax in developing countries.

(4) Septicaemia anthrax:

Cutaneous intestinal and pulmonary anthrax, if not treated in time, progress into septicaemia and death occurs from overwhelming infection.

Specimens: Pus, fluid, sputum or blood depend­ing on the type of lesion. Specimen must be labelled “High Risk”.

B. anthracis is capsulated, non-motile, large (5-8/1.5 μm), gram-positive rod with square ends. Spore forms never occur in tissues but develop after the organism is shed or if it is grown on artifi­cial media. Spores can be stained by modified Ziehl- Neelsen’s method. Capsules are formed in the tissues but are usually lacking in culture.

When B. anthracis in blood of animals in a heat fixed film is stained with polychrome methylene blue for 10-20 seconds, disintegrated capsular material appears amorphous and purplish around the bacilli.

B. anthracis is aerobe and facultative anaerobe, grows readily on ordinary media over a wide-range of temperature (25°-30°C), optimum 35°C. Colonies are 2-5 mm in diameter, dense, grey-white they are composed of parallel chains of cells producing wavy margin of the colony, the so-called ‘Medusa head’ or ‘curled hair lock’ appearance.

Colonies are non-haemolytic or only slightly haemolytic (saprophytic Bacilli species are markedly haemolytic).

Growth is not usually turbid but forms a thick pellicle on the surface.

3. Gelatin stab culture:

Growth occurs along the tract of inoculating wire with lateral spikes, widest near the surface — the “inverted fir tree” appear­ance, but the liquefaction is late.

When white mouse or guinea pig is intra-peritoneally inoculated with a small amount of exudate or, culture, the animal dies in 36-48 hours. Heart blood and sputum shows B. anthracis.

Bacillus subtilis:

It is a non-pathogenic saprophyte and appear as common contaminant of specimen and laboratory media.

Nutrient agar shows dry, 2-3 mm grey­ish-white opaque colonies. In nutrient broth, there is uniform turbidity.

Gram-positive bacilli with sub-terminal spore.

Non-pathogenic to labo­ratory animals. They also differ from B. anthracis in producing β-lactamase which is different from that produced by staphylococci and are motile.

Medium # 2. Blood Agar:

A. Streptococcus:

Streptococcus is a gram-positive coccus arranged in chain.

A. Haemolytic classification:

Preliminary classi­fication of streptococci is made based on the type of haemolysis produced on blood agar plates.

(i) β-haemolytic streptococci:

They produce a wide (2-4 mm wide) clear zone of complete haemolysis around the colony (Fig. 7.8).

(ii) α-haemolytic streptococci:

They produce a partial haemolysis (1-2 mm wide) with greenish discolouration. Some un-haemolysed RBCs are detectable in the haemolytic zone. Alpha haemolysis is seen in pneumococcus and viridans streptococci.

(iii) γ-haemolytic streptococci:

They produce no haemolysis and Streptococcus faecalis is a typical member.

B. Serological classification (Lancefield and Griffith classification):

The β-haemolytic strepto­cocci are classified by Lancefield (1933) serologically into a number of broad groups on the basis of group specific polysaccharide antigen of cell wall. To date, 20 Lancefield groups have been identified, numbered A-V (without I and J) by precipitation reaction with appropriate sera. Majority of the human pathogens belong to group A which are also called Streptococcus pyogenes.

The strains of group A streptococci are further subdivided by type specific antisera into 80 Griffith serotypes (type 1, type 2, etc.) according to their surface proteins (M, T and R). M protein is most important type specific antigen which exists in approximately 80 antigenic forms, each of which is present in a different serotype of S. pyogenes.

Streptococcus pyogenes:

Box 2 shows the important lesions produced by different species of streptococci.

Laboratory diagnosis:

A. Acute suppurative infections:

Specimen is collected from the site of lesion such as swab, pus or blood depending on the nature of infection, such as swabs taken from throat, vagina or purulent lesion of patients and from the throat and nose of suspected carriers.

Microscopy of smears of pus showing Gram-positive spherical or oval cocci in chains or pairs in association with pus cells suggests the presence of streptococci (Fig. 7.7). Non-viable organisms are gram-variable.

Specimen should be inoculated immediately or sent to the laboratory in Pike’s transport medium (blood agar containing 1 in 1,000,000 crystal violet and 1 in 16,000 sodium azide). Specimen is inoculated in blood agar medium and incubated at 37°C overnight. Haemolysis develops better under anaerobic conditions or under 5-10% carbon dioxide.

Sheep blood agar is preferable as human blood may contain inhibitors. The bacterial colonies are small, typically matt or dry and surrounded by β-haemolysis. Haemophilus haemolyticus produces colonies resembling those of β-haemolytic streptococci but their haemolysis is inhibited by sheep blood. Hence primary isolation should be done in sheep blood agar.

Serological testing for determination of Lance- field group and Griffith type of haemolytic streptococci is done when needed for definite classification and for epidemiological study.

A simple technique of detection of S. pyogenes (group A) is done by agar plate test using paper discs impregnated with bacitracin. S. pyogenes is more sensitive to bacitracin than other streptococci. Selective media like crystal violet blood agar that inhibits throat commensals and may facilitate the detection of small numbers of S. pyogenes in throat swabs, but are rarely used in routine culture.

3. Antigen detection tests:

Commercial test kits of ELISA, and agglutination tests are now available to demonstrate group A streptococcal antigen from throat swabs which are 75-80% sensitive.

Commercial test kit of a nucleic acid probe-based test for direct detection of group A streptococci in throat swabs is available.

Although antibodies to most toxins and enzymes of group A streptococci are produced, these antibodies appear late, hence test for antibodies is not helpful in diagnosing acute infection. They are more commonly used to diagnose non-suppurative complications.

B. Non-suppurative complication:

Culture of throat swab or pus from skin lesions helpful for checking the continuing presence of S. pyogenes in throat or impetigo. Serological tests provide evidence of recent streptococcal infection. A rising titre of antibodies to group A streptococcal antigens are usually detectable. ASO titre of 200 units or more is significant in rheumatic fever.

ASO titre is usually found in high levels in respiratory disease and rheumatic fever but in streptococcal skin infections and acute glomerulonephritis, ASO titre tends to be low and DNase-B test is more reliable. Complement (C3) level is also reduced in serum in acute post-streptococcal glomerulone­phritis.

B. Proteus, Morganella, Providencia:

Human and animal intestine. Some species are saprophytes and are found in soil, sewage and water.

P. mirabilis is the most important, other species are occasionally encountered in human lesions.

1. Urinary tract infection, especially following catheterization or cystoscopy.

2. Sepsis: Abdominal, wound and middle ear infections. The organisms are generally low grade pathogens and often are secondary invader of ulcers, pressure sores, burns and damaged tissues.

Laboratory diagnosis:

Depending on the site of infection, which include urine, pus, blood.

These are actively motile, non-capsulate, gram- negative pleomorphic bacilli.

Proteus species grow well on routine media (nutrient agar, blood agar) with a swarming type of growth. This makes the isolation of other bacteria difficult in mixed cultures because swarming from a single colony of Proteus may cover the whole plate culture.

However, swarming is inhibited in media containing bile salts, sewage. MacConkey agar, DCA and XLD agar. Swarming is also inhibited by increasing agar concentration (2%), chloral hydrate (1:500) and boric acid (1:1000) by incorporating in the media.

Colourless, non-lactose fermenting on Mac­Conkey agar. Proteus cultures have a distinctive smell (fishy/seminal).

In a mixed culture, pathogen can be separated from Proteus contaminated plate by sub-culturing in MacConkey agar. Swarming is not exhibited by the Morganella and Providencia.

Table 7.9 shows the distinctive biochemical cha­racters of the three genera.

1. Lactose is not fermented by any of the three genera, hence colonies are pale on MacConkey or DCA.

2. All produce indole except P. mirabilis, and only two members (P. mirabilis and P. vulgaris) produce H2S.

3. All members produce phenylalanine deaminase and deaminate phenylalanine to phenyl pyruvic acid (PPA).

4. Production of urease and hydrolysis of urea is another characteristic of all members of the group except P. stuartii which is urease-negative.

Differentiation from the common pale colonies of pathogens isolated on lactose containing media is made by testing urease activity. Shigella and Salmonella do not produce urease.

Certain antigens (alkali-stable fraction O) of Proteus strains (0 x 19, 0 x K and 0 x 2) are common to Rickettsial prowazekii and agglutinate with sera from patients with rickettsial disease. This antigen sharing forms the basis of Weil-Felix reaction (heterophile agglutination test).

Citrobacter, Enterobacter, Serratia:

Citrobacter, Enterobacter and Serratia species are Gram-negative motile rods and opportunistic patho­gens.

They are found in intestinal tract of man and animal, and in soil, sewage and water.

These members grow well on routine media such as MacConkey agar, blood agar and nutrient agar.

Citrobacters are late or non- lactose fermenters and enterobacters are lactose fermenters. Serratia is a non-lactose fermenting organism. Some strains of Serratia produce red pigment.

Medically important species include C. freundii, E. aerogenes, E. cloacae and S. marcescens.

1. Urinary tract infection.

2. Wounds, skin lesions and respiratory infections in hospitalized patients.

3. Septicaemia: Some are responsible for out­breaks of infection in nursery, ICU and burns units. They are often multi-drug resistant.

Medium # 3. MacConKey’s Agar:

I. Lactose Fermenters:


The classification of Enterobacteriaceae is complex and controversial. There has been successive changes in the nomenclature of taxonomy with DNA homology studies. More than 30 genera and 120 species or groups have been defined, about 96% of the medically important isolates belong to 14 genera and constitute 38 species.

The oldest method of classification of enteric bacilli is based on lactose fermentation and members fermenting lactose are called lactose fermenters or coliforms.

b. Escherichia Coli:

The main species of medical importance is Esche­richia coli which are gram-negative motile bacilli.

E. coli is a normal inhabitant of intestinal tract of humans and animals.

UTI, wound infection, peritonitis, biliary tract infection, septicaemia, neonatal meningitis.

Infant gastroenteritis (EPEC), travellers’ diarrhoea (ETEC), haemorrhagic dia­rrhoea (VTEC) (haemorrhagic colitis, haemolytic uraemic syndrome).

E. coli is an important cause of sepsis:

(a) Urinary tract infection including cystitis, pyelitis and pyelonephritis.

(b) Wound infections, appendicitis, peritonitis, biliary tract infection.

II. Diarrhoea:

Despite being a normal gut flora, four pathogenic groups of E. coli are recognised that cause diarrhoea.

(a) Enterotoxigenic E. coli (ETEC):

E. coli produces either one or two plasmid mediated enterotoxins, heat-labile enterotoxin (LT) and heat-stable enterotoxin (ST).

LT stimulate adenyl cyclase in mucosal cells of small intestine, which, in turn, activates cyclic adenosine monophosphate (cAMP) that causes hyper secretion of fluid and electrolytes into the intestinal lumen and produces watery diarrhoea. In contrast, ST appears to activate guanylate cyclase and cause diarrhoea.

(b) Enteroinvasive E. coli (EIEC):

The EIEC are far less pathogenic than ETEC and invade the mucosa of colon and cause a dysentery like shigella dysentery in all age groups. They are non-motile and resemble shigella strains in their biochemical reaction (NLF). Important serogroups are O 124 and O 164.

(c) Enteropathogenic E. coli (EPEC):

EPEC is an important cause of outbreak of infantile gastro­enteritis in developed countries.

(d) Verocytotoxigenic E. coli (VTEC):

VTEC are named so because of the cytopathic effect of their toxins on vero-monkey kidney cells. There are two antigenically distinct verocytotoxins — VT-1 and VT-2. Commonest VTEC is a serogroup O 157 that causes haemorrhagic colitis and haemolytic uraemic syndrome in children.

Laboratory diagnosis:

Depending on the site of infection specimens are collected which include urine, pus, blood and stool. In case of diarrhoeal diseases, faeces may be examined for toxin detection.

E. coli is a gram-negative motile rod. A few strains are non-motile (formerly referred to as Alkalescens dispar group). Some E. coli strains are capsulated.

Specimen is inoculated on MacConkey agar and blood agar plates and incubated at 37°C for over­night.

The colonies are 1-4 mm in diameter, pink, circular, convex, smooth and usually non- viscous in MacConkey agar (Fig. 7.8).

Colonies may be haemolytic.

Growth on other media:

Most strains do not grow or markedly inhibited in xylose-lysine-deoxycholate (XLD), DCA and SS agar.

IMViC reactions with Esch. coli are: Indole positive methyl red positive, VP negative and Simmon’s citrate negative (IMViC ++- – ).

The isolated organism is confirmed by aggluti­nation test, first with polyvalent and then by individual specific O antisera. More than 164 E. coli serogroups are identified. H and K antigens of many of these serogroups have been identified.

Bacterial count in bacteriuria:

In urinary tract infection, sample of unspun mid­stream urine is inoculated in MacConkey’s agar and blood agar and incubated for overnight at 37°C. An estimate of the number of organism per ml of unspun urine sample is made by counting the number of colonies formed.

The loop of an inocula­tion wire is made such that a loopful amount of sample equals a volume of 0.01 ml. As each bacterial colony represents progeny of a single bacterium, the colony count in the plate when multiplied by 100 gives the bacterial count per ml sample. When bacterial count is 10 5 (100,000) or more per ml of urine in untreated cases of UTI, it is called significant bacteriuria.

When bacterial count is between 10,000 to 100,000 per ml, the culture may be repeated. Counts of 10,000 or less per ml are due to conta­mination during voiding and are insignificant. However, bacterial count in UTI may be lower than 100,000 per ml. in certain conditions, e.g. when the patient is on antibiotic therapy and in coccal infections (S. aureus, S. faecalis).

It is a non-motile, capsulated gram-negative rod and produces mucoid colony in solid media.

They are widely distributed in nature occurring both as commensals in human and animal mouth, upper respiratory tract and intestine, as well as saprophytes in soil, water and vegetation.

Biochemically and antigenically, Klebsiella is classified as:

1. K. pneumoniae — also called K. aero genes.

(a) K. pneumoniae:

1. Urinary tract infection, particularly those that are hospital acquired.

2. Respiratory tract infection: Occasionally it causes pneumonia.

4. Meningitis (especially in neonates).

5. Rarely abscesses, endocarditis, peritonitis and other lesions.

It causes rhinoscleroma, a chronic granulomatous growth of nose and pharynx.

It causes ozena in nasal mucosa, a disease characterised by foul-smelling nasal dis­charge with progressive atrophy of mucosal mem­branes.

Urine, sputum, pus and infected tissue depending upon site of lesion.

Gram-negative, non-motile, capsulated rods.

Large and usually mucoid colonies (due to production of extracellular slime) on MacConkey agar and blood agar. Majority of the stains produce pink colonies and MacConkey’s medium due to lactose fermentation.

Lactose fermenter, indole negative and citrate positive (see Escherichia coli). IMViC reactions are IMViC – – + + . Majority of Klebsiella strains are urease- producers but much slower and less intense in this regard than the Proteus strains.

More than 80 capsular types have been identified. Identification by Quelling reaction is recommended.

Urinary tract infection:

3. Proteus spp, especially P. mirabilis.

5. Occasionally Enterobacter, Citrobacter, Ps. aeruginosa and Serratia.

Significant bacteriuria:

When bacterial count is 10 5 (100,000) or more per ml of unspun urine sample in untreated cases of UTI, it is called significant bacteriuria.

A standard calibrated loop of 3 mm internal diameter that can hold 1/300 ml urine is used for transferring undiluted urine sample for inoculation into MacConkey agar and blood agar and then the plates are incubated overnight.

II. Non-Lactose Fermenters:

Most salmonellae are found in the gut of animals especially of pigs, cows, goats, sheep’s, rodents, hens, ducks and other poultry. They are pathogenic for their hosts and also cause disease in man. S. typhi and S. paratyphi differ from other salmonellae, in that man is the only natural host.

Salmonellae produce 3 main types of lesions but mixed forms are common.

2. Paratyphoid fever — S. paratyphi A, B and C.

(b) Food poisoning (gastroenteritis):

2. S. enteritidis phase type 4.

(c) Septicaemia with or without local suppurative lesion:

S. typhi is ingested with conta­minated food and water. The organisms then pass from small intestine into blood (transient bacte­remia) via mesenteric lymph nodes and thoracic duct. Blood stream is rapidly cleared by mono­nuclear phagocytic system in the liver, spleen and gallbladder.

From the gallbladder the organisms invade the Peyer’s patches of intestine causing inflammation and ulceration. The bacilli then pass into blood leading to bacteraemia and generalized infection. Organisms are excreted in faeces and urine in third and fourth week.

Clinically, the disease is generally milder than typhoid fever with shorter duration and incubation. S. paratyphi A and C infections are more common in tropical countries.

S. paratyphi C: It mainly causes septicaemia and important lesions caused by the organism include formation of abscess, arthritis and inflammation of gallbladder.

3. Food poisoning (enterocolitis):

Salmonella food-poisoning is caused by ingestion of contaminated food like meat, egg and milk with S. typhimurium and S. enteritidis. Symptoms occur within 10-30 hours. Food-poisoning strains can also cause septicaemia, inflammation of gallbladder and osteitis. Salmonellae causing septicaemia occasionally cause localised pyogenic lesions, such as, osteomye­litis, meningitis and deep abscesses.

Laboratory diagnosis:

Culture and isolation of salmonellae are essential to confirm a diagnosis. Identification of the isolate is based on biochemical characteristics and serology. The optimal specimen for culture varies with presen­tation.

(a) In a classic case of salmonella gastroenteritis faecal sample is best. Patients’ vomitus and suspe­cted foodstuffs are also useful.

(b) In a suspected case of enteric fever, blood culture or bone marrow aspirate is most likely to yield positive results. Later, with intestinal and renal involvement, culture of faeces and urine is indicated.

The specimens to be tested at different stages of enteric fever and the percentage of positivity are shown in Fig. 7.9 and Table 7.11. General blood picture in enteric fever may show leucopenia (leucocyte count, 2,000-2,500 cumm) with relative lymphocytosis.

Isolation of the organism:

Specimens of blood or bone marrow in enteric fever faeces, vomitus or suspected food in gastroenteritis should be collected before starting treatment. As there is transient bacteraemia, there are small number of organisms in blood. Repeated culture with larger volume (5-10 ml) of blood is necessary. Blood culture is positive in 80-90% patients in first week and up to 10 days of fever.

The chances of positive culture progressively diminishes with increase in duration of illness (Fig. 7.9). Blood culture also yields positive result during relapses. Bone- marrow material culture is as reliable as blood culture and it yields positive result in 1 to 2 days after commencement of chloramphenicol therapy.

A volume of 5 to 10 ml blood collected aseptically by venepuncture is transferred directly into a blood culture bottle containing 50 to 100 ml 0.5% glucose broth or 0.5% bile broth. Although blood culture in bile broth (selective medium for salmonellae) is most ideal for salmonellae, but in practice most laboratories use glucose broth for blood culture because all microorganisms including salmonellae grow in the medium.

Larger volume of media helps in dilution of the antibacterial substances present in the blood Liquid (sodium polyanethol sulphonate) may be added in the media which counteracts the bactericidal action of blood.

Alternatively, 5 ml venous blood, collected aseptically, is allowed to clot in a sterile screw- capped universal container. After removing serum, 15 ml bile salt streptokinase broth streptokinase, 100 units per ml) is added aseptically to each bottle.

The streptokinase digests the clot causing its lysis and thereby the bacteria are released from the clot. The separated serum is utilised for Widal test. Clot culture offers a higher rate of isolation than blood culture as the bactericidal activity of serum is obviated in the technique.

After incubation overnight at 37°C , sub-culturing is done on MacConkey agar or DCA. Sub-culturing is economically carried out by spreading a loopful of broth over a sector of solid media, one-fourth of an 8.5 cm Petri dish and incubated for 24-48 hours. Colourless colonies (NLF) appear. Cultures may be discarded as negative after 10 days.

As growth may be delayed and also to eliminate the risk of introducing contamination during repeated subcultures, Castaneda’s method of blood culture may be adopted, which provides both liquid (liver infusion broth) and solid media (3% nutrient agar slope) in one bottle. It is a diphasic medium, the broth has an agar slant on one side.

2. Stool and urine culture:

Culture of faeces and urine are always positive during 3rd and 4th week of enteric fever. Repeated cultures are required for positive result. Stool culture is mainly done for detecting the carriers.

3. Duodenal juice or bile culture:

Bile is cultured to detect chronic carriers in whom the organisms are present in the biliary tract.

In MacConkey’s agar or DCA, salmonellae grow as non-lactose fermenters which are further studied by Gram’s staining, motility preparation and biochemical reactions in different sugar media. Subculture from the colonies is made in nutrient agar to be utilised for agglutination test.

Slide agglutination test:

A loopful of isolated orga­nism (unknown culture) from the colony in agar is emulsified in a drop of saline on a microscopic slide without spreading the drop. The emulsion must be absolutely smooth and of medium opacity. One small loopful of specific antiserum is added and then mixed by tilting the slide.

In the same way, a control of bacterial suspension in normal saline is prepared on another slide and to which no specific serum is added. Clumping of bacteria in test slide occurs within a few minutes if the antigen-antibody reaction is specific. Control saline emulsion of bacteria does not show any change.

Biochemically positive strains (Box 3) are first tested with polyvalent O serum, which reacts with salmonella strains in groups A to G, provided agglutination is not blocked by Vi antigen, which can be checked by testing all negative strains using S. typhi Vi serum. Positive results with polyvalent O serum indicates a Salmonella strain.

In the next step, the strain is tested with sera prepared against O antigens of the individual salmonella groups. The following are the most useful sera which react with factor 2, Group A factors 4 and 5, group B with 6 and 7, group C1 with 8, group C2 with 9, group D and with 3, 10, 15 and 19, group E.

When the strain is positive with individual salmo­nella O serum, and biochemically it is typically S. typhi, the strain is tested against S. typhi O serum, factor 9. Prompt agglutination indicates that the microorganism belongs to Salmonella group D. Its identity is established as S. typhi by agglutination with salmonella H specific serum which reacts with flagellar antigen d.

In a non-typhoid salmonella, the strain is tested for agglutination with O and H sera for groups A, B and C. When unusual serotypes are encountered, the same should be referred to the National Salmonella Reference Centre (Central Research Institute, Kasauli, for human strain, and Indian Veterinary Research Institute, Izatnagar, for salmo­nella of animal origin).

Subtyping methods are frequently used for the common serotypes (S. typhi, S. typhi- murium and S. enteritidis) which include phage typing, bio-typing, and more recently introduced genotyping methods (plasmid finger printing). These techniques are employed in CDC for subtyping within serotypes of Salmonella.

It is an agglutination test which detects presence of serum agglutinins (H and O) in patient’s serum with typhoid and paratyphoid fever. Salmonella antibody starts appearing in serum at the end of first week and rises sharply during the 3rd week of enteric fever.

It is preferable to test two specimens of sera at an interval of 7 to 10 days to demonstrate a rising antibody titre. Convalescent sera from salmonella gastroenteritis cases often agglutinate a suspension of the causal serotype which helps in retrospective diagnosis.

In Widal test, two types of tubes were originally used: (i) Dreyer’s tube (narrow tube with conical bottom) for H agglutination, and (ii) Felix tube (short round-bottomed tube) for O aggluti­nation. Nowadays 3 x 0.5 ml Kahn tubes are used for both types of agglutination.

A serial two fold dilution of patient’s serum in normal saline (1: 20, 1: 40 and so on up to 1,280 or more) is prepared in 8 small (3 x 0.5 ml) test tubes for each series 7 for serum dilutions and 8th for a non-serum control.

To the diluted serum and control saline equal volume (0.4 cc) of antigen suspensions (TH, TO, AH and BH) are added and mixed thoroughly by shaking the rack and then the mixtures are incubated at 37°C for 4 hours and read after overnight refrigeration at 4°C. Some workers recommended incubation in a water bath at 37°C overnight.

Loose and cotton-woolly clumps are formed in H agglutination and a disc-like granular deposit in O agglutination at the bottom of tube. Control tube shows a compact deposit. The Maxi­mum dilution of serum at which agglutination occurs indicate the titre of antibodies.

The routinely used antigens are H and O of S. typhi, H of S. paratyphi A and B. As paratyphoid O antigen cross reacts with typhoid O antigen due to the sharing of factor 12 by them, paratyphoid O antigens are not used.

Preparation of Widal antigen:

H suspension of bacteria is prepared by adding 0.1% formalin to a 24 hours broth culture or saline suspension of an agar culture. For preparation of O suspension of bacteria, the organisms are cultured on phenol agar (1: 800). Standard smooth strains of the organism are used S. typhi 901, O and H strains are employed for this purpose.

Interpretation of Widal test:

1. Agglutinin starts appearing in serum by the end of 1st week with sharp rise in 2nd and 3rd weeks and the titre remains steady till the 4th week after which it declines.

Demonstration of rising titre of four-fold or greater of both H and O agglutinins at an interval of 4 to 7 days is the most important diagnostic criterion.

3. In a single test, a titre of 100 of O or more and a titre of 200 of H agglutinins signifies presence of active infection, but that has to be interpreted taking into consideration the following factors:

Due to sub-clinical infection of salmonellosis in endemic area, low titre of agglu­tinins is present in the serum of normal individuals, which may cause positive reaction. This is known as local titre. Local titre is up to 80 in Kolkata and 60 in Siliguri.

In immunization with TAB vaccine, vaccinated individuals may show high titres of antibody (H antibody titre 160 or more) to each of the salmonellae.

(iii) Anamnestic reaction:

Persons who had past enteric infection or who have been vaccinated may develop transient fever like malaria, influenza etc.

(iv) Non-specific antigens (e.g. fimbrial antigen) may produce false positive result.

(v) Antibiotic treatment:

When treatment with chloramphenicol is started before the appearance of agglutinins, they are unlikely to appear subse­quently if the antibody is already present, no further rise in titre is expected.

Widal tests may be negative in many healthy carriers and some have to be detected by Vi agglutination test.

2. Other serological tests:

ELISA is sensitive method of measuring antibody against the lipopolysaccharide of Salmonellae, titre of IgM antibody corresponds fairly well with the Widal O titre. ELISA in vertical flow membrane format (Typhi- DOT) detects Vi Ag in blood/serum at an early stage of the disease.

Shigella species are exclusively parasites of human and other primates and cause bacillary dysentery in man.

Shigellae are gram-negative non- motile bacilli. Antigenically, shigellae are divided into four groups (A, B, C, D) based on specificity of O antigen. These groups are differentiated by a combination of biochemical reactions and antigenic structure. Mannitol fermentation reactions are important, group A is mannitol negative and the rest are mannitol positive.

Shigella species cause bacillary dysentery (shi­gellosis). Infection is transmitted by faecal-oral route. S. dysenteriae type 1 (S. shiga) produces exotoxins that causes most severe form of disease. S. flexneri and S. boydii cause less severe dysentery and are prevalent in tropical countries including India. S. sonnei is the cause of most dysentery in Britain.

The organisms are taken up by the epithelial cells of distal parts of the colon with necrosis of surface epithelial cells leading to an acute inflammation in lamina propria and sub-mucosa. Necrotic epithelia sloughs forming superficial ulcers which leads to bleeding mucosa.

Laboratory diagnosis:

To confirm diagnosis, shigella must be isolated in pure culture from an adequate sample. Specimens include fresh stool, mucous flakes, and rectal swabs.

A. Microscopical examination of stool:

Cover slip preparation in saline and iodine shows large number of pus cells (neutrophils) with degenerated nuclei, RBC, and macrophages. The presence of protozoa, cysts or helminthic ova is excluded. The normal bacterial flora is considerably diminished. Fluorescent antibody technique is of some help in rapid diagnosis of a case but it is not usually practiced.

B. Bacteriological examination:

MacConkey’s agar, DCA, S-S agar, Selenite F broth.

A loopful of material is inoculated on selective media like MacConkey’s agar or SS agar media.

Selenite-F broth (0.4%) is used as enrichment and transport medium which permits rapid growth of enteric pathogens while temporarily (for 9-12 hours) inhibiting the growth of E. coli. Organisms from selenite-F broth are sub-cultured in MacConkey’s agar after 24 hours incubation at 37°C.

Colourless colonies appear on MacConkey’s agar medium after 12 to 18 hours incubation which is further tested by smear examination, motility preparation and biochemical reactions. Shigellae are Gram-negative non-motile bacilli.

II. Biochemical reactions:

Urease, citrate, H2S and KCN negative indole and M R positive Gram-negative non-sporing bacillus is suggestive of a shigella strain (Fig. 7.10). S. sonnei is a late lactose fermenter.

III. Slide agglutination test:

It is done by using polyvalent antisera of three groups (A, B and C) of shigella and antiserum of group D (S. sonnei), one by one against the isolate. Monovalent antisera are used for the group for which agglutination has occurred with polyvalent antisera. Then type specific antisera for strains belonging to Group A, B or C is used for agglutination test.

Occasionally, agglutination may not occur due to masking of O antigen by K antigen, which can be removed by boiling the bacterial suspension at 100°C for 60 minutes.

It is done for group D strains.

V. Sereny test may be done to confirm the invasiveness of the isolated strain of shigella, although, it is seldom practiced.


Botulism Risk of Canned Beans

Bacteria need water to grow and die without a water source. Moist areas are particularly prone to bacterial growth, such as bathrooms and kitchens. Water content in food also provides an excellent environment for many types of bacteria to grow. Certain foods can be dehydrated or freeze-dried, which removes most of the water and can allow for longer storage without bacterial growth. Moist tissues in the body, such as the mouth and nose, provide an excellent source of moisture for bacteria and are particularly prone to bacterial growth.

  • Bacteria need water to grow and die without a water source.
  • Moist tissues in the body, such as the mouth and nose, provide an excellent source of moisture for bacteria and are particularly prone to bacterial growth.

Understanding the Microbiome in Your Mouth

“Your mouth mirrors what is happening in your body,” says biologic dentist Gerry Curatola. For over thirty-five years, Curatola has been treating patients with periodontal conditions at his practice in New York City. In his book, a gum issue is rarely, if ever, just a gum issue.

Curatola’s background in alternative medicine partly explains his holistic approach: He attended Harvard Medical School’s program in Complementary and Alternative Medicine after graduating from the New York University College of Dentistry. (He now serves as adjunct clinical associate professor in NYU’s Department of Cariology and Comprehensive Care.) He’s also spent decades conducting and studying oral microbiome research. (There’s a wing in his name at NYU for translational research, which applies tools from basic biology and clinical trials to address critical health needs.)

And then there’s what Curatola has observed in the dental chair: Healing the body helps heal the mouth, and vice versa. While bacteria are often blamed for problems like tooth decay and gum disease, Curatola says there’s no such thing as good bacteria or bad bacteria. Bacteria either behave well or poorly, depending on the condition of their terrain. Which is why he focuses on maintaining homeostasis within the oral microbiome. This is slightly more involved than brushing your teeth after dinner and calling it a day, says Curatola, but it’s simple enough to manage once you know how.

A Q&A with Gerry Curatola, DDS

The understanding of the entire human microbiome has helped us redefine what it means to be human. We are a composite of many species, and there is a symbiotic relationship between man and microbe that is foundational to our ability stay alive and thrive with countless bodily functions. In the mouth, this unique community of mostly bacterial organisms, known as the oral microbiome, is an intelligent, semipermeable membrane that performs vital functions to help keep our mouths healthy. These functions include transporting ionic minerals from saliva to the surface of teeth to aid in remineralization, carrying molecular oxygen to the gums and soft tissue, and eliminating free radicals and other waste products from the surface. In addition to these important functions, the oral microbiome plays a vital role in protecting us from harmful environmental organisms.

When the oral microbiome is in a state of balance, otherwise known as microbial homeostasis, its nature is very different from its nature when it’s in an imbalanced state. The ecosystems in your mouth are referred to as the oral biofilm, or plaque. A balanced oral microbiome consists of bacteria that are mostly aerobic—meaning they rely on oxygen to live. They form a thin, protective, clear, and odorless film. Your teeth feel squeaky-clean and your gums appear pink and well oxygenated in this balanced state.

When imbalanced, this biofilm transforms into a thick, sticky, and smelly film, which is commonly observed as the off-white plaque film on your teeth in the morning. Often this repetitive formation results from constant disturbances of the oral microbiome. It is important to note that in the human microbiome there is no such thing as “good bacteria” and “bad bacteria.” Rather, it’s just bacteria that behave well (probiotics), or those that behave poorly (pathogens), depending on the condition of their terrain. A number of species of bacteria in the mouth associated with tooth decay and gum disease are totally benign in a balanced oral microbiome.

Symptoms that often signal an imbalanced oral microbiome include bad breath, bleeding gums, and frequent tooth decay. Each of these symptoms is a sign of an imbalance that is connected to the microbiome being too thick, called a hypertrophic biofilm.

An imbalance can also show up as an atrophic biofilm, which means it’s too thin. This results in mouth ulcers and sensitive teeth. I often compare flossing or cleansing between teeth to picking up the garbage on the side streets in New York City on a warm summer day. If you don’t, it will only get worse, and issues will continue to arise. It’s important to include interdental cleansing—whether with floss, interdental brushes, or picks—as part of your oral-hygiene regimen.

Constant disturbances to this essential ecology in the mouth can cause the oral microbiome to be in a continual state of imbalance. Disturbances can include harmful oral-care products, a diet high in refined carbohydrates and sugar, a low pH in the mouth, and stress.

Many oral-care products were developed by soap manufacturers over a hundred years ago and are detergent- or alcohol-based and tough on the microbiome. Our focus for the past fifty years has been on eradicating this microbial community, viewing bacteria as “invaders” that should be “killed on contact.” Even many natural oral-care products that are focused on “killing plaque” with natural essential oils can be harmful to the important function of the oral microbiome.

At my practice, we help our patients understand what I call the three important commandments of the human microbiome.

  1. We are made up of microbes.
  2. These microbes run us.
  3. The best way to stay healthy in every respect, including our oral health, is to make peace with our microbes.

That has been the core philosophy behind the research and efficacy of the Revitin Toothpaste, which I spent fifteen years developing.

Another cause of imbalance is a diet high in sugar and refined carbohydrates. Carbohydrates and sugar produce acid that eats away at the enamel and causes tooth decay. A diet high in refined carbohydrates and sugar can cause a shift in the oral microbiome from slightly alkaline to a more acidic pH. This causes a shift in the corresponding flora in the mouth.

Another major culprit that leads to an imbalance is stress. Stress causes a cascade of events that, in turn, stresses the oral microbiome. First and most important, it causes a decrease in salivary flow. Saliva is the lifeblood of the mouth, and it is essential for the oral immune system and continuous remineralization of teeth. The oral microbiome interacts with saliva by carrying ionic minerals like calcium and phosphorus from saliva to the surface of tooth enamel. Stress also causes a shift in the pH to a more acidic environment and promotes unhealthy grinding and clenching of teeth and jaw discomfort.

The germ theory, which is now outdated, stated that bacteria were the cause of both tooth decay and gum disease. We now know that this is not the case—and that naturopathic medicine had it right all along. Naturopaths have always said that disease is about not the seed (bacteria) but the soil (microbial terrain). The causes of both tooth decay and gum disease are imbalances of the terrain—the oral microbiome. It’s really an amazing paradigm shift in scientific understanding.

In 2009, The Journal of the American Dental Association (JADA) declared that periodontal disease is an archetypal biofilm disease. In other words, there is not one specific bacteria but rather a community environment problem that can lead to gum disease. The shift in the environment of the oral microbiome from microbial homeostasis—a balanced terrain with mostly aerobic bacteria—to an imbalanced, hypertrophic biofilm results in the unfavorable propagation of anaerobic bacteria. This includes the growth of Streptococcus mutans bacteria, most associated with tooth decay, and Porphymonas gingervalis bacteria, which are associated with the periodontal inflammation and progression of gum disease. Keeping the oral microbiome terrain balanced is essential to keeping this progression in check.

In The Mouth-Body Connection, I outline the four cornerstones to promoting a healthy mouth and a balanced oral microbiome.

The first is to take inventory of what oral-care products you are using and then eliminate products that might strip and/or destroy the microbiome. This includes detergent-based toothpastes and alcohol-containing mouthwashes. I recommend staying away from ingredients like:

  • Sodium laurel sulfate (SLS)
  • Sodium fluoride
  • Triclosan
  • Artificial sweeteners (such as sodium saccharin, aspartame, xylitol, and erythritol)
  • Artificial color dyes (often made from coal tar)
  • Propylene glycol
  • Diethanolamine (DEA)
  • Microbeads (tiny solid plastic particles)

The second is what I call Triple-A nutrition: foods that are alkalizing, anti-inflammatory, and antioxidant-rich, along with supporting supplements. For example, eating organic fruits and vegetables and natural and organically raised meat, fish, poultry, and eggs eating and drinking fermented foods—like kombucha, sauerkraut, and dill pickles—on a regular basis drinking herbal teas and coffee in moderation and using filtered water for cooking and drinking.

For more than thirty-five years, I observed well-intentioned patients who told me they spent “hours in the bathroom” on their oral-hygiene regimen, but they continued to be prone to dental decay and gum disease. It became obvious that there was a multifactorial basis to this. Nutrition always seemed to be a cornerstone of oral health and critical in helping keep the pH and microbial terrain in balance.

The third is healthy exercise. Movement and high-intensity exercise techniques for as little as fifteen minutes a day can help decrease the stress-induced, inflammatory flight-or-fight response. Exercise has been shown to increase circulatory function—including for teeth and gums—and improve immune system competence. The increase in circulation that is gained during exercise has been shown to improve the prevention of decay by improving the dentinal tubular fluid flow, which is a continuous movement of nourishing interstitial liquid that flows from the tissues inside the tooth outward through the enamel and into the mouth. Blood supply is the major route via which all organs are nourished and defended, and one major cause of disease and malfunction is restricted blood supply. In the teeth, the blood supply ends in the capillaries within the dental pulp, and it has been observed that restricted blood supply in teeth increases tooth decay.

Finally, the fourth key to a balanced microbiome is stress management. As previously mentioned, stress plays an important role in salivary function, as well as muscular control, TMJ, and overall tooth and gum health. Stress can contribute to grinding your teeth—or bruxism—which can wear down and flatten your teeth. Constant grinding depletes your enamel, causing your teeth to become more sensitive. Grinding can also impact the joints and muscles in the jaw and neck, which can lead to jaw pain and clicking or popping sounds. Stress can also dry out your mouth, which can contribute to gum disease. I advise patients to begin incorporating yoga and meditation into their lives not only to improve their breathing and other body vitals but also to help keep their microbial flora in balance.

Gerry Curatola, DDS, is a biologic restorative dentist and the founder of Rejuvenation Dentistry. He studied neuroscience at Colgate University and attended dental school at the New York University College of Dentistry, where he now serves as an adjunct clinical associate professor in the Department of Cariology and Comprehensive Care. He studied nutrition and wellness at the Pratt Institute and completed Harvard Medical School’s program in complementary and alternative medicine. He’s the author of The Mouth-Body Connection.

This article is for informational purposes only, even if and to the extent that it features the advice of physicians and medical practitioners. This article is not, nor is it intended to be, a substitute for professional medical advice, diagnosis, or treatment and should never be relied upon for specific medical advice. The views expressed in this article are the views of the expert and do not necessarily represent the views of goop.

Serratia Marcescens as a Cancer Therapy?

Prodigiosin taken from strains of S. marcescens has been shown to be toxic to cancerous cells but much less so to non-cancerous ones. Because of this, prodigiosin is currently being studied as a natural medicine for cancer therapy. Cell toxicity – even to healthy cells – has always been a problem in the development of anticancer drugs. Microorganism metabolites such as prodigiosin – the pigment that produces the red coloration in S. marcescens colonies – inhibit certain cancer cell signaling pathways causing early cancer cell death however, the exact action is not yet understood. Current studies have shown anticancerous activity of prodigiosin in breast cancer, prostate cancer, and choriocarcinoma although all of these studies took place in the laboratory. This area of study is known as bacteria-mediated cancer therapy or BMCT and is becoming increasingly popular as a pharmaceutical industry research topic.

1. Which of these numbers represents a 5-log reduction?
A. 9999%
B. 99%
C. 9999 log
D. 999%

2. SSR refers to:
A. Starvation-stress cross-reference response
B. Starvation-survival response
C. Starvation-induced cross-resistance response
D. Starvation-stress response

3. What is BMTC?
A. A type of bacterial resistance to antimicrobial drugs
B. A pigment found in S. marcescens bacteria
C. Therapy for cancer using products produced by some single-celled microorganisms
D. A temperature-linked mechanism that increases bacterial survival in higher temperatures

How bacteria break down human food

Last weeks post on the changing composition of bacteria in the vagina generated a lot of interest, and as there's been quite a of talk about the human microbiome (all the bacteria that live on the human body) at the moment I thought I'd stick with the theme. This weeks post is about how bacteria break down the nutrients that humans eat and use them to create their own food.

The paper (reference 1 below) from PLoS One focuses on carbohydrates. Starting with some biochemistry background: carbohydrates are molecules made exclusively from carbon, hydrogen and oxygen (hence the name). These three molecules are arranged into a ring structure for the simple carbohydrates such as glucose, and those rings are put together into long complex branching chains for the complex carbohydrates such as starch and cellulose.

Simple carbohydrates, like the glucose shown in the picture above, are fairly easy to metabolise and can be used to power-up ATP (the molecules that the cell uses for energy) or in the synthesis of proteins. More complex carbohydrates like starch or cellulose (shown below) take a bit more effort, as they need to be broken down into their component simple sugars before they can be processed. To break them down bacteria use a specific group of enzymes called CAZymes which stands for “Carbohydrate-active enzymes". As enzymes are very specialised in the molecules that they break down, different CAZymes exist for different complex carbohydrates.

Different bacteria will have different CAZymes, but an intriguing question the PLoS paper set out to answer is how the pattern of CAZymes changes throughout the body. There isn't just one bacterial species inside you, but many, each species differently related to the ones surrounding it. It's less a community of bacteria inside you and more like a badly organised safari park, with different species all milling around in close proximity to each other, relying on the resources available in whichever part of the body they happen to live in.

The researchers compared the carbohydrate digesting abilities of 493 bacterial genomes, associated with five different sites on the exterior and interior of the human body. When they tried to work out the number and distribution of CAZymes by species they very quickly ran into difficulties. Some bacterial families, such as Bacillaceae, had an average of number of 25 sugar-cleaving enzymes, with a respectable standard deviation of 3.3 (for the uninitiated, the standard deviation measures how likely each individual is to be close to the average). The bacterial family Clostridiaceae on the other hand had an average of 56 sugar-cleaving enzymes but with a standard deviation of 79! As well as showing the large inter-species variation, this also makes it difficult to predict relatedness between bacteria based on their carbohydrate-digesting abilities.

As comparing species didn't seem to be yielding particularly concise results, the researchers then moved onto comparing CAZymes by bacterial habitat. Unlike humans, and indeed pretty much all eukaryotes, bacteria don't just pass genes down to their offspring, they can also pass genes across to a nearby friend. Unsurprisingly, bacteria living in the same place on the body tended to have more similar carbohydrate-digesting enzymes than bacteria that were more related by species. Overall the researchers found four major patterns of carbohydrate-use:

1) Bacteria in the nose and nasal cavities - unsurprisingly these bacteria tended to have very little carbohydrate metabolising ability (very few people inhale starch)

2) Bacteria in the vagina - These bacteria tended to be breaking down more simple sugars, and also had carbohydrate forming enzymes in order to build up biofilms

3) Bacteria in the mouth - these bacteria have a wide range of carbohydrate digesting enzymes in order to break down the bits of food which get trapped in your teeth. The researchers also identified three enzymes used for metabolising dextran, which may be unique for mouth-bacteria and seemed to be a marker for plaque formation.

4) Bacteria in the gut - this is where the big carbohydrate-digesting muscle lies! Not only do gut bacteria have plenty of CAZymes for human carbohydrates, they also have range that deal with plant carbohydrates. Many of these bacteria have the ability to form a cellulosome - a large complex of cellulose digesting enzymes all held together by scaffold proteins.

It may be slightly weird to think of bacteria living in so many parts of your body - colonising your spaces and eating your food - but really, it would have been much more of a surprise to find they weren't. Pretty much every surface on earth has bacteria living on it, and humans are such a warm, moist, nutrient-rich surface that they provide a great living environment for a huge number of bacterial species.

Cantarel BL, Lombard V, & Henrissat B (2012). Complex carbohydrate utilization by the healthy human microbiome. PloS one, 7 (6) PMID: 22719820

The views expressed are those of the author(s) and are not necessarily those of Scientific American.


A biochemist with a love of microbiology, the Lab Rat enjoys exploring, reading about and writing about bacteria. Having finally managed to tear herself away from university, she now works for a small company in Cambridge where she turns data into manageable words and awesome graphs.

Watch the video: Η κοκκινοσκουφίτσα έγκυος (September 2022).


  1. Lauriano

    the message is removed

  2. Yozshutaxe

    At you a migraine today?

  3. Mimi

    An appeal against this.

  4. Erysichthon

    Wacker, what phrase ..., a splendid thought

  5. Nastas

    I squint slyly, comparing the facts ... *

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