Question 1

Name the two reagents that are needed to visualize nitrite in the nitrate reduction test.
A) Sulfanilic acid and 40% sodium hydroxide
B) Sulfuric acid and $\alpha$-naphthol
C) N,N-dimethyl-$\alpha$-naphthylamine and sulfanilic acid
D) N,N-dimethyl-$\alpha$-naphthylamine and sulfuric acid

Accepted Answer

The two reagents needed to visualize nitrite in the nitrate reduction test are N,N-dimethyl-α-naphthylamine and sulfanilic acid. Choice C contains the correct reagents. Choice A contains sulfanilic acid but not the correct second reagent. Choice B contains sulfuric acid but not the correct second reagent. Choice D contains the correct second reagent but not sulfanilic acid.

Question 2

What medium is used in the urease test?
A) Christensen media
B) Loeffler's media
C) Moeller's oxidative broth
D) Kovac's reagent

Accepted Answer

Christensen media is used in the urease test to detect the enzyme urease, which hydrolyzes urea into ammonia and carbon dioxide. The media contains a pH indicator that changes from yellow to pink in the presence of ammonia, indicating a positive result for urease activity. Loeffler's media is used to cultivate diphtheria bacteria, Moeller's oxidative broth is used to test for the ability of organisms to produce catalase, and Kovac's reagent is used in the indole test to detect the production of indole by some bacteria.

Question 3

This identification system for Enterobacteriaceae has a series of 20 cupules attached to a plastic strip. Inside the cupules are lyophilized pH-based substrates. What is the name of this system?
A) ID Tri-Panel
B) API 20E
C) Microbact
D) Enterotube II

Accepted Answer

The API 20E system is a biochemical panel for identification and differentiation of members of the family Enterobacteriaceae. It consists of 20 microtubes (cupules) containing dehydrated substrates that, when rehydrated with bacterial suspension, allow various metabolic reactions to be observed, typically based on pH changes.

Question 4

Rapid identification of clinical isolates often involves commercially packaged identification kits and fully automated instruments. What do these kits use to assess the preformed bacterial enzymes?
A) Extraction kits
B) Volatile benzenes
C) Chromogenic or fluorogenic substrates
D) Chemiluminescent substrates

Accepted Answer

Chromogenic or fluorogenic substrates are commonly used in commercially packaged identification kits and fully automated instruments to assess the preformed bacterial enzymes. These substrates are designed to react with specific enzymes and produce a color or fluorescent signal, which can then be used to identify the bacterial species present in the sample. This method is both rapid and reliable, making it a popular choice in clinical microbiology laboratories.

Question 5

Commercial identification systems fall into all of the following categories, except
A) pH-based reactions.
B) enzyme-based reactions.
C) visual detection of bacterial growth.
D) use of nitrogen and sulfur sources.

Accepted Answer

Commercial identification systems typically do not categorize based on the use of nitrogen and sulfur sources. They focus on pH-based reactions, enzyme-based reactions, and visual detection of bacterial growth.

Question 6

What does a lysine iron agar (LIA) slant contain?
A) Ornithine, glucose, ferric ammonium chloride, and urea
B) Lysine, glucose, ferric ammonium citrate, and sodium thiosulfate
C) Acetoin, pyruvic acid, nitrate, and sulfanilic acid
D) Arginine, lactose, ferric chloride, sodium hydroxide, and urea

Accepted Answer

A LIA slant contains lysine as a source of amino acid, glucose as a source of carbohydrate, ferric ammonium citrate as an indicator of hydrogen sulfide production, and sodium thiosulfate as a source of sulfur. The other choices (A, C, and D) are incorrect as they contain different combinations of components that are not present in a LIA slant.

Question 7

How are organisms identified with commercial identification kits?
A) Numeric codes
B) Color codes
C) Alphabetic codes
D) Alphanumeric codes

Accepted Answer

The answer of How are organisms identified with commercial identification...

Question 8

What advantage do the methods based on enzyme substrates have over conventional methods?
A) They use filter paper as the structure to hold the bacteria.
B) They reduce the amount of substrate needed for the reactions.
C) They use fluorogenic substrates.
D) They do not require growth of the organism in the system.

Accepted Answer

Methods based on enzyme substrates do not require growth of the organism in the system, which can save time and resources compared to conventional methods that require cultivation of the bacteria. Option A is incorrect because filter paper is not a unique advantage of using enzyme substrates. Option B is incorrect because some conventional methods may also use small amounts of substrate. Option C is incorrect because not all enzyme substrates use fluorogenic substrates.

Question 9

The LIA slant is also useful in differentiating
A) Acinetobacter and Alcaligenes.
B) Klebsiella and Enterobacteriaceae.
C) Proteus, Morganella, and Providencia.
D) Escherichia, Salmonella, and Campylobacter.

Accepted Answer

The LIA slant is useful in differentiating between Proteus, Morganella, and Providencia. These species have different patterns of amino acid metabolism, which can be observed in the medium. Acinetobacter and Alcaligenes do not typically produce the types of amino acid metabolites that can be differentiated on the LIA slant. Klebsiella and Enterobacteriaceae can be differentiated using other biochemical tests, such as the oxidase and citrate tests. Escherichia, Salmonella, and Campylobacter are not typically tested using the LIA slant, as they do not produce the types of amino acid metabolites that can be differentiated on this medium.

Question 10

What does the oxidase test determine?
A) If the bacteria have the enzyme, oxidase, to reduce oxygen to carbon dioxide
B) If the bacteria have oxidase, which will allow for the oxidation of carbohydrates
C) If the bacteria can hydrolyze urea to ammonia and carbon dioxide
D) The presence of the cytochrome oxidase system that oxidizes reduced cytochrome with molecular oxygen

Accepted Answer

The oxidase test is used to determine the presence of the cytochrome oxidase system in bacteria, which is responsible for oxidizing reduced cytochrome with molecular oxygen. Option A and B are incorrect because the oxidase test is not related to the oxidation of carbohydrates or the reduction of oxygen to carbon dioxide. Option C is incorrect because it refers to the urease test, not the oxidase test.

Quiz 9: Biochemical Identification of Gram-Negative Bacteria

Name the two reagents that are needed to visualize nitrite in the nitrate reduction test.

What medium is used in the urease test?

This identification system for Enterobacteriaceae has a series of 20 cupules attached to a plastic strip. Inside the cupules are lyophilized pH-based substrates. What is the name of this system?

Rapid identification of clinical isolates often involves commercially packaged identification kits and fully automated instruments. What do these kits use to assess the preformed bacterial enzymes?

Commercial identification systems fall into all of the following categories, except

What does a lysine iron agar (LIA) slant contain?

How are organisms identified with commercial identification kits?

What advantage do the methods based on enzyme substrates have over conventional methods?

The LIA slant is also useful in differentiating

What does the oxidase test determine?