Question 1

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) Utilization of nitrogen and sulfur sources

Accepted Answer

Commercial identification systems fall into one of five categories or a combination thereof: pH-based reactions,enzyme-based reactions,utilization of carbon sources,visual detection of bacterial growth,or detection of volatile or nonvolatile fatty acids by gas chromatography.

Question 2

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 helpful in differentiating between the Enterobacteriaceae,oxidase negative,and the pseudomonads.When a 1% aqueous solution of tetramethyl-p-phenylenediamine dihydrochloride is added,the development of a lavender color is positive.

Question 3

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

Accepted Answer

These numeric codes are generated based on the metabolic profiles of each organism.Each metabolic reaction,or phenotype,is translated into one of two responses: + or -.These plus/minus sequences are cataloged as binary numbers and stored in a computer database.

Question 4

What type of medium is used in the motility test?
A) Semisolid
B) Cornmeal
C) Sabouraud dextrose
D) Peptone gel

Accepted Answer

Motility is determined by observing growth in semisolid medium.The motility test media have agar concentrations of 0.4% or less,to allow for free spread of organisms.Cornmeal and Sabouraud dextrose are two media used for fungal cultures.

Question 5

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

Because enzymatic methods involve preformed enzymes,they do not require multiplication of the organism (growth independent).Therefore endpoints are reached in minutes to a few hours.

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

The components of this slant include lysine,glucose,ferric ammonium citrate,and sodium thiosulfate.LIA is used primarily to determine whether the bacterial species decarboxylates or deaminates lysine.Hydrogen sulfide production is also detected in this medium.

Question 7

The Vitek AutoMicrobic System is manufactured by:
A) Abbott
B) bioMériux
C) Dade Behring
D) Becton Dickinson

Accepted Answer

bioMériux makes the Vitek AutoMicrobic System.

Question 8

The lysine iron agar (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

This group of enterics deaminates (attacks the NH₂ group instead of the carboxyl group)amino acids.In the LIA slant,deamination of lysine turns the original light purple color slant to a plum or reddish purple color; the butt turns yellow because of glucose fermentation.

Question 9

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

The chromogenic substrates are colorless; when cleaved by a microbial enzyme,a colored compound is produced.Fluorogenic substrates are nonfluorescent until cleaved by microbial enzymes.Reaction endpoints may be reached after 2 to 6 hours of incubation.

Question 10

A positive test for motility:
A) Turns the motility media blue
B) Shows hazy appearance throughout or movement away from a stab
C) Appears as a scum on the top of the media
D) Will turn blue after the addition of the indicator bromthymol blue

Accepted Answer

Motile organisms will move away from the stab line or will move throughout the media.Motility media do not have indicators added to them.The bacteria do not form a scum on the top of the media; they stay in the media and spread out there.

Question 11

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 Analytical Profile Index (API 20E)has a series of 20 cupules attached to a plastic strip with lyophilized pH-based substrates inside the cupules.The principles of the tests are similar to those performed in the test tubes.

Question 12

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 a-naphthol
C) N,N-dimethyl-a-naphthylamine and sulfanilic acid
D) N,N-dimethyl-a-naphthylamine and sulfuric acid

Accepted Answer

The organism is inoculated into a nutrient broth containing a nitrogen source.After 24 hours of incubation,N,N-dimethyl-a-naphthylamine and sulfanilic acid are added.A red color indicates the presence of nitrite.

Question 13

This system is widely used in microbiology laboratories today.
A) MicroScan
B) Mueller-Hinton
C) Enterotube
D) API 20E

Accepted Answer

The MicroScan system consists of plastic,standard-sized 96-well microtiter trays in which up to 32 reagent substrates are included for the identification of bacteria and yeast.

Question 14

This system provides rapid identification of gram-negative bacteria through the use of cards.
A) MicroScan
B) BD Phoenix 100
C) Vitek AutoMicrobic system
D) Sherlock Microbial Identification system

Accepted Answer

MicroScan and BD Phoenix use microtiter panels.The Serlock Microbial Identification system uses a gas chromatograph to identify bacteria.

Question 15

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

Accepted Answer

Christensen's urea agar is generally preferred.It contains urea and phenol red as the indicator.A positive test turns a bright pink test.Kovac's reagent is used for the indole test.

Quiz 9: Biochemical Identification of Gram-Negative Bacteria

Commercial identification systems fall into all of the following categories EXCEPT:

What does the oxidase test determine?

How are organisms identified with commercial identification kits?

What type of medium is used in the motility test?

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

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

The Vitek AutoMicrobic System is manufactured by:

The lysine iron agar (LIA) slant is also useful in differentiating:

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 positive test for motility:

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?

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

This system is widely used in microbiology laboratories today.

This system provides rapid identification of gram-negative bacteria through the use of cards.

What medium is used in the urease test?