Deck 9: Biochemical Identification of Gram-Negative Bacteria

Question 1

When performing the oxidative/fermentative (O/F)test,one tube is covered with mineral oil and one tube is left uncovered.Why is one tube covered with mineral oil?

A) To create an anaerobic (fermentative) environment
B) To create an aerobic (oxidative) environment
C) To create a reductive environment
D) To create an asaccharolytic environment

Answer 1

A
When O/F tests are performed,two tubes of OFBM are inoculated; one is overlayed with sterile mineral oil to create an anaerobic environment (closed),and the other tube is left aerobic (open),without mineral oil overlay.This allows the bacteria the opportunity to oxidize or ferment the carbohydrates present in this media.The O/F tests do not create reductive or asaccharolytic environments.

Question 2

Biochemical tests are based on the _____ of microorganisms.

A) Phenotype
B) Genotype
C) Plasmid
D) Lysogeny

Answer 2

A
The colony morphology,Gram stain,and biochemical testing are based on the phenotype of the bacterium.The phenotype is the expressed characteristics in the bacteria.The genotype is the actual nucleic acid sequences present in the bacterium's DNA.Plasmids can be responsible for antimicrobial resistance,but they do not alter colony morphology or biochemical tests.Lysogeny is infection of the bacteria with a virus.

Question 3

The methyl red test detects metabolic by-products from what pathway?

A) Mixed acid fermentation pathway
B) Butylene glycol pathway
C) Citrate pathway
D) Clark and Lubs pathway

Answer 3

A
Glucose is metabolized via the Embden-Meyerhof pathway,producing several intermediate by-products,including pyruvic acid.Further degradation of pyruvic acid can produce mixed acids as final end products.However,enterics take two separate pathways: the mixed acid fermentation pathway or the butylenes glycol pathway.The methyl red test detects the end products from the mixed acid pathway.

Question 4

During this process,glucose enters the glycolysis pathway,resulting in the formation of pyruvic acid,which is further oxidized to other acids.What is this process called?

A) Oxidation
B) Reduction
C) Fermentation
D) Synthesis

Question 5

Bacteria can utilize carbohydrates by:

A) Oxidation
B) Synthesis
C) Reduction
D) Induction

Question 6

Other sugars that bacteria can use to produce energy for glucose include all of the following EXCEPT:

A) Raffinose
B) Arabinose
C) Rhamnose
D) Sucralose

Question 7

If a bacterium utilizes lactose or sucrose,what will the triple sugar iron (TSI)reaction look like?

A) Alkaline/acid
B) Alkaline/alkaline
C) Acid/acid
D) Acid/alkaline

Question 8

What chemicals are added to triple sugar iron (TSI)to detect the production of hydrogen sulfide gas?

A) Phenol red and ferrous sulfate
B) Bromthymol blue and sodium thiosulfate
C) Ferrous sulfate and sodium thiosulfate
D) Copper sulfate and ferrous sulfate

Question 9

If a bacterium utilizes lactose or sucrose and produces H₂S,what will the triple sugar iron (TSI)reaction look like?

A) Acid/acid, black butt
B) Acid/alkaline, black butt
C) Alkaline/alkaline, black slant
D) Alkaline/acid, black slant

Question 10

To inoculate triple sugar iron (TSI)agar or Kligler's iron agar (KIA),the laboratory scientist should pick a well-isolated colony with an inoculating needle and:

A) Touch the bottom of the needle to the bottom of the slant portion of the agar and move the needle back and forth across the surface of the slant all the way to the top of the tube.
B) Touch the bottom of the needle to the top of the slant portion of the agar and move the needle back and forth across the surface of the slant all the way to the bottom of the tube.
C) Touch the bottom of the needle to the bottom of the slant portion of the agar and move the needle up the slant in a straight line all the way to the top of the tube.
D) Stab the butt almost all the way to the bottom of the tube, then move the needle back and forth over the surface of the slant all the way to the top of the tube.

Question 11

These bacteria are unable to ferment either lactose or glucose,but they can degrade the peptones present in the triple sugar iron (TSI)agar or Kligler's iron agar (KIA)aerobically or anaerobically,resulting in the production of alkaline by-products in the slant or deep,respectively,changing the indicator to a deep red color.What kind of bacteria cannot ferment lactose or glucose?

A) Nonenteric bacilli
B) Anaerobic bacilli
C) Gram-positive cocci
D) Gram-positive rods

Question 12

Nucleic acid assays are based on the _____ of the organism and are believed to be more accurate.

A) Phenotype
B) Genotype
C) Plasmid
D) Lysogeny

Question 13

This test determines if an organism is a delayed lactose-fermenter.

A) b-Galactosidase
B) Dihydroxylase
C) Nitrate
D) Ortho-Nitrophenyl-b-D-galactopyranoside (ONPG) test

Question 14

What are the sugars present in triple sugar iron (TSI)?

A) Sucrose, glucose, lactose
B) Mannitol, lactose, arabinose
C) Sucrose, glucose, rhamnose
D) Lactose, sucrose, raffinose

Question 15

Some bacteria are asaccharolytic.This means that these bacteria:

A) Ferment glucose and use the Embden-Meyerhof pathway
B) Do not utilize any carbohydrate; instead they use other organic molecules for energy
C) Reduce glucose-that is, send it through the Entner-Doudoroff pathway
D) Induce glucose into glycolysis so that it can be oxidized

Question 16

Oxidative/fermentative (O/F)basal medium is a medium that will test the oxidative and fermentative capabilities of a microbe.The pH indicator is _____.

A) Sudan IV
B) Phenolphthalein
C) Bromcresol green
D) Bromthymol blue

Question 17

If an organism fermented glucose only and utilized peptones,what would the triple sugar iron (TSI)reaction be?

A) Acid/acid
B) Alkaline/acid
C) Alkaline/alkaline
D) Acid/alkaline

Question 18

A tech is reading the biochemical tests for identifying a particular gram-negative rod.The organism has produced acid,indicated by a color change,in the closed tube only.This indicates that the organism is:

A) An oxidizer
B) A fermenter
C) Both an oxidizer and a fermenter
D) A reducer

Question 19

The initial screening of gram-negative rods is done by testing for the utilization of this carbohydrate.

A) Glucose
B) Sucrose
C) Lactose
D) Mannitol

Question 20

The chemical reaction for the Ortho-Nitrophenyl-b-D-galactopyranoside (ONPG)test is:

A) b-galactosidase hydrolyzes lactose into glucose and galactose
B) Glucose ® pyruvic acid ® acetoin
C) b-Galactosidase hydrolyzes o-nitrophenyl-b-D-galactopyranoside into galactose and o-nitrophenol (a yellow compound)
D) O-nitrophenyl-b-D-galactopyranoside is oxidized into acetoin and glucose

Question 21

The medium used in the decarboxylase test is called:

A) Clark's decarboxylase base medium
B) Voges decarboxylase base medium
C) Möeller decarboxylase base medium
D) OF decarboxylase base medium

Question 22

What indicator is used in the methyl red test?

A) Bromthymol blue
B) Phenolphthalein
C) Methyl red
D) Bromcresol green

Question 23

Extracellular DNAase can be produced by:

A) Staphylococcus aureus
B) Streptococcus agalactiae
C) Micrococcus luteus
D) Haemophilus influenzae

Question 24

A bacterial DNAase is:

A) An oligonucleotide formed from a native DNA
B) An oligonucleotide formed from a native RNA
C) A proteolytic enzyme that forms extracellular DNA in the bacterial cell
D) An endonuclease that cleaves internal phosphodiester bonds, resulting in smaller subunits of DNA

Question 25

What two reagents can be used to visualize indole in the broth?

A) Indole and xylene
B) 40% sodium hydroxide and a-naphthol
C) 10% ferric chloride
D) Ehrlich's and Kovac's

Question 26

Amino acids can be metabolized by these substances that remove an amine group.What is this substance?

A) Amino acidase
B) Amylase
C) Deaminase
D) Decarboxylase

Question 27

Using Möeller's decarboxylase base medium,what color is a positive reaction and what causes this color to be produced?

A) Purple, alkaline environment produced
B) Yellow, acid environment produced
C) Purple, acid environment produced
D) Yellow, alkaline environment produced

Question 28

Some bacteria produce these enzymes that break down gelatin into amino acids.These enzymes are called:

A) DNAase
B) Gelatinase
C) Proteolytic
D) Malonase

Question 29

This test is useful in the initial differentiation of Proteus,Morganella,and Providencia species from the rest of the Enterobacteriaceae.

A) Oxidation-fermentation
B) Methyl red
C) Amino acid decarboxylase
D) Phenylalanine deaminase

Question 30

In the Voges-Proskauer test,you are testing for the metabolic by-products of which pathway?

A) Glucose ® formic acid ® formaldehyde
B) Glucose ® pyruvic acid ® mixed acid fermentation
C) Lactose ® glucose ® 2,3 butanediol
D) Glucose ® pyruvic acid ® acetoin ® diacetyl KOH

Question 31

Decarboxylase tests exist for all the following amino acids EXCEPT:

A) Lysine
B) Tyrosine
C) Ornithine
D) Arginine

Question 32

This reagent is used to demonstrate a positive phenylalanine deaminase test.

A) 10% ferric chloride
B) Methyl red
C) a-Naphthol
D) 40% sodium hydroxide

Question 33

The principle of the citrate test includes all the following EXCEPT:

A) Bacteria able to use citrate will use the ammonium salts releasing ammonia.
B) The alkaline pH that results from use of the ammonium salts changes the pH indicator.
C) The pH indicator changes from red to bright yellow.
D) The pH indicator changes from green to blue.

Question 34

Bacteria demonstrating weak decarboxylase activity:

A) Will have a false-negative test
B) May take up to 4 days to be positive
C) Require extra reagents to show the positive reaction
D) Will have a false-positive test

Question 35

What test determines whether an organism can utilize sodium citrate as a sole carbon source?

A) Ornithine decarboxylase
B) Citrate
C) Indole
D) Ehrlich's reagent

Question 36

Why does the Möeller decarboxylase base medium contain glucose if it is testing the decarboxylation of amino acids?

A) The decarboxylation of the amino acids takes place during the glucose metabolic pathway. Once glucose is broken down into pyruvic acid, then the amino acid is modified.
B) To get the energy needed to take the carboxyl group off the amino acid, the bacteria must have glucose.
C) When glucose is fermented, one of the by-products is acetoin. This acetoin is part of the mechanism that cleaves the carboxyl group from the specific amino acid.
D) Decarboxylases are inducible enzymes produced in an acid pH.

Question 37

The biochemical pathway that the methyl red test confirms is:

A) Glucose ® pyruvic acid ® mixed acid fermentation
B) Pyruvic acid ® glucose ® mixed acid fermentation
C) Glucose ® pyruvic acid ® acetoin ® diacetyl KOH
D) Butylene ® pyruvic acid ® diacetyl KOH

Question 38

The two reagents used in the Voges-Proskauer Test are:

A) Methyl red and acetoin
B) 40% KOH and methyl red
C) o-Nitrophenol and a-naphthol
D) 40% KOH and a-naphthol

Question 39

What amino acid is the substrate in indole test broth?

A) Ornithine
B) Arginine
C) Tryptophan
D) Leucine

Question 40

The decarboxylase tests determine:

A) Whether the bacteria possess enzymes capable of removing the carboxyl group of specific amino acids in the test medium
B) Whether the bacteria can further metabolize the acids formed during fermentation to 2,3 butanediol
C) If bacteria can maintain an acid pH if only sucrose is present in the media
D) To see if a-naphthol can be broken down into its constituent parts: acetoin and diacetyl KOH

Question 41

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

Question 42

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

Question 43

How are organisms identified with commercial identification kits?

A) Numeric codes
B) Color codes
C) Alphabetic codes
D) Alphanumeric codes

Question 44

What type of medium is used in the motility test?

A) Semisolid
B) Cornmeal
C) Sabouraud dextrose
D) Peptone gel

Question 45

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.

Question 46

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

Question 47

The Vitek AutoMicrobic System is manufactured by:

A) Abbott
B) bioMériux
C) Dade Behring
D) Becton Dickinson

Question 48

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

Question 49

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

Question 50

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

Question 51

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

Question 52

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

Question 53

This system is widely used in microbiology laboratories today.

A) MicroScan
B) Mueller-Hinton
C) Enterotube
D) API 20E

Question 54

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

Question 55

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