Clinical Bacteriology

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Questions and Answers

What does a positive result for hydrogen sulfide production indicate in the context of the Proteus test?

The organism is unable to ferment sugars.

The organism produces ammonia from urea.

The organism reduces sulfate to hydrogen sulfide. (correct)

The organism oxidizes amino acids.

What is the primary purpose of the urease test?

To detect the presence of hydrogen sulfide.

To identify if the organism can ferment glucose.

To determine if the organism hydrolyzes urea to ammonia. (correct)

To measure the capability of organisms to utilize citrate.

Which biochemical result would not occur in Proteus according to the provided data?

Nitrate reduction.

Indole production.

Hydrogen sulfide production. (correct)

Urease activity.

In the context of the SIM test, which characteristic does the semi-solid medium help to determine?

The motility of the organism. Signup and view all the answers

What does a positive result in the nitrate reduction test indicate?

The organism can reduce nitrate to nitrite or other nitrogenous compounds. Signup and view all the answers

What medium is used for conducting the urease test?

Christensen's Urea Agar. Signup and view all the answers

Which indicator is used in the urease test to detect pH changes?

Phenol Red. Signup and view all the answers

What is the significance of the mixed acid fermentation (MR) test?

It indicates the ability to carry out mixed-acid fermentation. Signup and view all the answers

What indicates a positive result in the Indole Test?

Red ring formation Signup and view all the answers

What does the Methyl Red Test indicate about an organism's metabolic pathway?

Uses mixed acids for glucose fermentation Signup and view all the answers

In citrate utilization testing, what does a deep blue color indicate?

Positive citrate utilization Signup and view all the answers

What is the primary purpose of the IMVIC test series?

To classify Gram-negative bacilli Signup and view all the answers

What is the indicator used in the Methyl Red Test?

Methyl Red Signup and view all the answers

Which test is used to detect hydrogen sulfide production in bacteria?

Triple Sugar Iron (TSI) Test Signup and view all the answers

What does a red coloration in the Methyl Red Test signify?

Acidic environment below pH 4.4 Signup and view all the answers

What is the substrate used in the Indole Test medium?

Tryptophan Signup and view all the answers

What is the expected interpretation of a positive indole test?

Indicates the organism can metabolize tryptophan. Signup and view all the answers

Which of the following correctly describes the significance of the methyl red (MR) test?

Indicates a strong acid fermenter. Signup and view all the answers

What does a positive citrate test indicate?

The organism can utilize citrate as its sole carbon source. Signup and view all the answers

How is hydrogen sulfide production detected in a culture medium?

By the formation of a black precipitate. Signup and view all the answers

What is indicated by a positive urease test?

Ability to hydrolyze urea to ammonia. Signup and view all the answers

The presence of a clear zone around a colony in a gelatin test indicates what?

The organism liquefies gelatin. Signup and view all the answers

Which of the following is involved in deamination of phenylalanine?

Conversion of phenylalanine to tyrosine. Signup and view all the answers

Which organism is indicated by a positive lysine decarboxylase (LDC) test?

Klebsiella oxytoca. Signup and view all the answers

Study Notes

Clinical Bacteriology - MT 6320

Order Enterobacterales: Various culture media used to differentiate gram-negative enteric bacteria.
- MacConkey Agar: Selects for gram-negative enterics. Contains bile salts, crystal violet, and neutral red. Differentiates lactose fermenters.
- Hektoen Enteric Agar: Selects for gram-negative bacteria. Contains bile salts, sodium citrate, and bromthymol blue. Used to differentiate bacteria.
- Salmonella Shigella Agar: Contains bile salts and brilliant green. Highly selective for Salmonella and Shigella differentiation.
- Xylitol Lysine Deoxycholate Agar: Selective for gram-negative enterics. Contains desoxycholate bile salts, citrate, phenol red, and other components.
- Bismuth Sulfite Agar: Selects for Salmonella typhi. Contains brilliant green, bismuth sulfite, and ferrous sulfate.

Culture Medium Characteristics

Color of Fermenter: Pink-purple for E. coli, Enterobacter, Klebsiella using either Eosin Methylene Blue (EMB)
Color Non-Fermenter: Yellow-colorless, and varied colors for other species
Culture specifics: Methods to test carbohydrate fermentation, H2S production and other properties.
Autoclave: Information about autoclave sterilization procedures and materials

Biochemical Tests

Indole Test: Detects tryptophanase production. Positive result is a red ring.
Methyl Red Test: Measures mixed-acid fermentation. Positive result is red.
Voges-Proskauer Test: Detects 2,3-butanediol fermentation products. Positive result is red.
Citrate Utilization Test: Determines if an organism can use citrate as its primary carbon source. Positive result is a change in color.
Oxidase Test: Identifies bacteria possessing cytochrome c oxidase. A positive result is a color change.
Catalase Test: Detects the presence of the enzyme catalase. Positive result is the production of oxygen bubbles.
Urease Test: Determines if an organism can hydrolyze urea. Positive result is a color change.
DNase test: Detects DNAse production (hydrolysis of DNA). Positive result is a clear zone around the organism.
Gelatinase Test: Identifies organisms capable of hydrolyzing gelatin. Positive result is a liquefied zone around the organism.
Decarboxylase test: Identifies organisms capable of deaminating amino acids. Positive result is a change in color. (Lysine, Ornithine, Arginine)
Nitrate reduction test: Detects ability to reduce nitrate to nitrite and further to nitrogen gas.
ONPG test: Detects the presence of beta-galactosidase. A positive result is a color change.

Additional Information

Salmonella, Shigella, Enterobacter, Klebsiella, Proteus, Serratia, Providencia are some of the genera tested.
H2S indicator: Detects sulfur compounds.
Growth: The rate at which specific organisms grow using appropriate methods. Notes on the presence or absence of different growth patterns like mucoid, fish-eye, colony type, etc

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Description

Test your knowledge on the various culture media used to differentiate gram-negative enteric bacteria in Clinical Bacteriology. This quiz covers MacConkey Agar, Hektoen Enteric Agar, Salmonella Shigella Agar, and more. Understand their selective properties and the bacteria they distinguish.