Microbes of the Body: The Enterics
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Enteric bacteria are phenotypically similar to several other genera of Gram-negative rod-shaped bacteria, such as Pseudomonas and Vibrio. However, how do these bacteria differ in terms of glucose?
Enteric bacteria are phenotypically similar to several other genera of Gram-negative rod-shaped bacteria, such as Pseudomonas and Vibrio. However, how do these bacteria differ in terms of glucose? • Generally, a distinction can be made on the ability to ferment glucose; enteric bacteria all ferment glucose to acid end products while similar Gram-negative bacteria (e.g. Pseudomonas) cannot ferment glucose.
Describe Coliforms • Gram • shape • spore • Oxygen sensitivity • oxidase presence • lactose fermentation
Describe Coliforms • Gram • (-) • shape • rod • spore • no spores • Oxygen sensitivity • facultative • oxidase presence • oxidase negative • lactose fermentation • ferment lactose
True or False All enterics are coliforms; however, not all coliforms are enterics.
False All coliforms are enterics; however, not all enterics are coliforms.
Where, besides the body, can coliforms reside?
Coliforms can be colon-dwelling bacteria but can also be found in soil or on plants and decaying vegetation.
What enzyme is specific to fecal coliforms?
β-glucuronidase.
What does the enzyme oxidase do?
• Oxidase enzymes play a vital role in the electron transport system during aerobic respiration. • Cytochrome oxidase catalyzes the oxidation of a reduced cytochrome by O2, resulting in the formation of usually H2O or sometimes H2O2.
What kind of bacteria exhibit oxidase activity?
• Aerobic bacteria, as well as some facultative anerobes and microaerophiles, exhibit oxidase activity.
What is the actual agent that detects cytochrome c oxidase in the oxidase test? How does it work?
• tetramethyl-p-phenylenediamine • The dye changes color upon oxidation. • It only reacts with cytochrome c oxidase. (Remeber, all bacteria have terminal electron acceptors and some may not have Cytochrome C. • Thus, only bacteria that use this particular protein will react with tetramethyl- p-phenylenediamine and cause a color change.
Describe the following as oxidase negative or oxidase positive • Enterobacteriaceae • Pseudomonas
Describe the following as oxidase positive or oxidase negative • Enterobacteriaceae • oxidase-negative • Pseudomonas • oxidase-positive
IMViC tests are used primarily for the differeniation between which two coliforms?
• IMViC tests are used primarily for the differeniation of the two coliforms Escherichia coli and Enterobacter aerogenes
What does the indole test determine?
Tryptophan degradation
What is Kovac’s reagent made of?
mixture of of p- dimethylaminobenzaldehyde, butanol and HCl.
What does indole bond to in a positive indole test? What does it form?
• Indole is extracted from the medium (tryptone broth) into the reagent layer by the acidified alcohol component. • This forms a cherry red complex with the p-dimethylaminobenzaldehyde.
What bacteria species are differentiated with the indole test?
• E. coli • is indole-positive; • Enterobacter aerogenes • indole negative.
What is the most important ingredient in MRVP broth?
Glucose, bitch
• When _____________(E. aerogenes/E. coli) is grown in glucose broth, mixed acids (lactic, formic and acetic) are formed until a pH of 4-5 is reached. • In contrast, _____________(E. aerogenes /E. coli) converts the organic acids into non-acidic end products such as 2,3-butanediol.
• When E. coli is grown in glucose broth, mixed acids (lactic, formic and acetic) are formed until a pH of 4-5 is reached. • In contrast, E. aerogenes converts the organic acids into non-acidic end products such as 2,3-butanediol.
The initial pH of the MRVP broth is approximately ____
The initial pH of the MRVP broth is approximately 6
• The methyl red pH indicator turns red between pH 4.4 and 5, and remains yellow between pH 6 and 7. • A red color in the medium indicates a _______ MR test (mixed acid fermentation; E. coli). • A yellow color indicates a ______ MR test (E. aerogenes).
• The methyl red pH indicator turns red between pH 4.4 and 5, and remains yellow between pH 6 and 7. • A red color in the medium indicates a positive MR test (mixed acid fermentation; E. coli). • A yellow color indicates a negative MR test (E. aerogenes).
In the Vogues-Proskauer Test, how is 2,3-butanediol fermentation detected?
The VP test detects the pathway intermediate, acetylmethylcarbinol (a.k.a. acetoin).
What kind of biochemistry (chemicals, reactions, etc) occurs in the Vogues-Proskauer Test?
• Acetoin is oxidized by α-napthol (VP reagent A) to a diacetyl compound in the presence of KOH (VP reagent B) and O2. • The diacetyl compound then reacts with a guanidine group that is present in the peptone of the MR-VP medium to form a pink complex.
In the VP test, label each as acetoin positive or acetoin negative • E. aerogenes yields a positive test (pink) • E. coli is VP negative (yellow)
In the absence of fermentable sucrose, glucose, or lactose, some enteric bacteria are capable of using ______ as a carbon source.
In the absence of fermentable glucose or lactose, some enteric bacteria are capable of using citrate as a carbon source.
In citrate agar what is: • the sole nitrogen source • the sole carbon source • the pH indicator
In citrate agar what is: • the sole nitrogen source • ammonium • the sole carbon source • citrate • the pH indicator • bromthymol blue indicator • green at pH 6.8 • blue at pH > 7.6.
Out of E. coli and E. aerogenes, which utilizes citrate as a sole carbon source and grows on citrate medium, changing the color of the agar from green to deep “Prussian blue.”
E. aerogenes