Bacterial Characterization Tests

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Questions and Answers

How does thioglycolate broth function in differentiating bacteria based on their oxygen requirements?

It establishes an oxygen gradient, allowing bacteria to grow at their preferred oxygen concentration. (correct)
It neutralizes acids produced by fermentation, ensuring optimal bacterial growth.
It directly measures the oxygen consumption rate of bacteria.
It introduces oxygen into the media, promoting the growth of aerobic bacteria.

What does a positive result in the Simmon's Citrate test indicate about a bacterium?

It cannot grow in the presence of citrate.
It utilizes citrate as a carbon source, producing alkaline byproducts. (correct)
It reduces citrate, leading to a color change in the medium.
It ferments citrate, producing acidic byproducts.

Which reagent is essential for visualizing the presence of starch hydrolysis in a starch agar plate?

Methyl red
Iodine (correct)
Kovac's reagent
Bromothymol blue

The presence of what enzyme is indicated by a positive catalase test?

Catalase (A) Signup and view all the answers

What is the function of phenylalanine deaminase detected in the phenylalanine slant test?

To deaminate phenylalanine, releasing ammonia. (A) Signup and view all the answers

What does the methyl red test specifically detect?

The production of mixed acids via fermentation. (A) Signup and view all the answers

What is the primary purpose of a spirit blue plate?

To determine if a bacterium can produce lipase. (A) Signup and view all the answers

In the context of the referenced material, what is the function of Kovac's reagent?

Detecting indole production. (D) Signup and view all the answers

What is the role of resazurin in thioglycolate broth?

To indicate the presence of oxygen. (B) Signup and view all the answers

What is the primary purpose of the Voges-Proskauer (VP) test?

To detect the production of acetoin from glucose fermentation. (A) Signup and view all the answers

What is the purpose of Durham tubes in fermentation tests?

To detect the production of gas. (A) Signup and view all the answers

What indicates a positive result for nitrate reduction beyond just nitrite production?

The presence of nitrogen gas after adding reagents A, B, and C. (D) Signup and view all the answers

Which enzyme's activity is assessed when using a milk plate?

Caseinase. (A) Signup and view all the answers

What does a purple color change in decarboxylation tests signify?

Alkaline production due to decarboxylation of a specific amino acid. (D) Signup and view all the answers

How is the optimum temperature determined when assessing growth patterns?

By finding the tube with the highest optical density (OD). (D) Signup and view all the answers

In a triple sugar iron (TSI) test, what does the formation of a black precipitate indicate?

Hydrogen sulfide (H2S) production. (A) Signup and view all the answers

What does it mean if a bacteria cannot survive in oxygen?

It is an obligate anaerobe. (A) Signup and view all the answers

What result indicates that a bacterium makes urease?

Pink color change in the media. (D) Signup and view all the answers

How does semi-solid media with TTC aid in observing bacterial motility?

It allows visualization of bacterial movement from the inoculation point. (C) Signup and view all the answers

What component of Gram stain gives a positive result?

Crystal violet (B) Signup and view all the answers

How does the presence of a black precipitate in SIM medium specifically aid in identifying bacterial metabolic activity?

It reveals the bacterium's ability to reduce sulfur, producing H2S. (C) Signup and view all the answers

In the context of bacterial hemolysis, what distinguishes beta-hemolysis from alpha-hemolysis on a blood agar plate?

Beta-hemolysis results in complete clearing around colonies, whereas alpha-hemolysis results in a partial lysis and a green discoloration. (C) Signup and view all the answers

How does the oxidation-fermentation (OF) test differentiate between bacterial oxidative and fermentative metabolism of glucose?

It uses bromothymol blue to indicate acid production in both open (oxidative) and closed (fermentative) tubes. (D) Signup and view all the answers

What is the significance of testing a bacterium's susceptibility to various antibiotics?

To guide the selection of effective treatments by determining whether the bacterium is resistant, intermediate, or sensitive to each antibiotic. (B) Signup and view all the answers

How do capsule stains differ from Gram stains in determining a key characteristic of bacteria?

Capsule stains identify the presence of a protective outer layer, enhancing virulence, while Gram stains differentiate bacteria based on cell wall structure. (A) Signup and view all the answers

What is the purpose of incorporating peptone into various bacteriological media?

To provide a source of nitrogen and carbon, supporting bacterial growth. (C) Signup and view all the answers

How does assessing bacterial growth on a slant of Triple Sugar Iron (TSI) agar aid in differentiating among bacterial species?

By observing slant color, as a means to identify the bacteria's capacity to ferment three different sugars and produce hydrogen sulfide. (A) Signup and view all the answers

What is the purpose of incorporating trehalose into a fermentation test medium alongside other sugars and a pH indicator?

To serve as a substrate to determine if the bacteria can ferment trehalose, indicated by a color change from the pH indicator. (A) Signup and view all the answers

How does the gelatin stab test reveal whether a bacterium produces gelatinase?

By assessing if the gelatin remains solid after refrigeration, with liquefaction indicating gelatinase production. (C) Signup and view all the answers

What is the role of cysteine in the SIM (Sulfide, Indole, Motility) medium in evaluating bacterial characteristics?

It acts as a substrate for detecting sulfide production. (D) Signup and view all the answers

What is the purpose of using DNA and methyl green in a DNAse test agar?

DNA is the substrate acted upon by DNAse, while methyl green stains the intact DNA. (B) Signup and view all the answers

How does one determine the optimum temperature for bacterial growth based on observed growth patterns?

The optimum temperature is the one where the bacteria exhibits vigorous growth. (D) Signup and view all the answers

What specific component in the Spirit Blue agar enables the detection of lipase production by bacteria?

Tributyrin oil, which is a lipid. (C) Signup and view all the answers

What role does mineral oil play in the context of the oxidation-fermentation (OF) glucose test?

Mineral oil creates an anaerobic environment by preventing oxygen from entering the medium. (B) Signup and view all the answers

In nitrate reduction tests, why might zinc powder be added after the addition of reagents A and B?

To reduce any remaining nitrate to nitrite, confirming a negative result for nitrate reduction by the bacteria. (D) Signup and view all the answers

How does the concentration of agar in semi-solid media, used for motility testing, aid in observing bacterial movement?

Low agar concentration allows motile bacteria to disseminate, creating a visible zone of diffusion from the inoculation point. (D) Signup and view all the answers

What indicates a positive result for the breakdown of casein on a milk plate?

A halo or clear zone around bacterial growth, indicating casein hydrolysis. (C) Signup and view all the answers

In decarboxylation tests, what specific environmental condition is usually required to promote decarboxylase activity, and how is it achieved?

Anaerobic conditions, usually achieved by adding mineral oil to the top of the medium. (D) Signup and view all the answers

What is the primary purpose of using control tubes without the addition of specific substrates in various biochemical tests?

To ensure that any observed changes are due to the intended biochemical reaction and not the medium itself. (D) Signup and view all the answers

Why is it important to avoid shaking thioglycolate broth cultures during incubation for anaerobes and facultative anaerobes?

Shaking can introduce oxygen into the broth, which can inhibit the growth of anaerobes. (B) Signup and view all the answers

Flashcards

Hemolysis

The breakdown of red blood cells.

Motility Test

Used to test the motility of an organism, determining if it has flagella.

Simmon's Citrate Test

A test to determine if an organism can use citrate as its sole carbon source.

Gram Stain

A differential staining technique to classify bacteria based on their cell wall structure (positive or negative).