Deck 24: Vibrio, aeromonas, Plesiomonas Shigelloides, and Chromobacterium Violaceum

Question 1

An organism suspected of being one of the Vibrio spp.grew on MacConkey agar.To determine whether it was a vibrio cell or in the Enterobacteriaceae family,an oxidase test was performed on the colony.The results of the oxidase test,however,were negative.Which one of the following statements explains this discrepancy?

A)The oxidase test should be performed on TCBS agar,not MacConkey agar.
B)The oxidase test should be performed on a sheep blood agar plate to avoid false-negative results.
C)The pH of the MacConkey agar is most likely elevated to alkaline conditions.
D)No discrepancy is present.All vibrio cells are oxidase-negative.

Answer 1

B
The oxidase test must be performed on 5% sheep blood or on another medium without a fermentable sugar (e.g. ,lactose in MacConkey agar,sucrose in TCBS agar).The reason for this is that fermentation of a carbohydrate results in acidification of the medium,and a false-negative oxidase test may result if the surrounding pH is below 5.1.

Question 2

Transmission of C.violaceum to humans is by:

A)exposure of disrupted skin to contaminated water.
B)ingestion of contaminated seafood or water.
C)inhalation of contaminated air.
D)close contact with carriers of the organism.

Answer 2

A
None of these organisms are considered part of the normal human flora;therefore,no carriers are known to exist.Transmission to humans is by ingestion of contaminated water or seafood or by exposure of disrupted skin and mucosal surfaces to contaminated water.

Question 3

Which organism,which is oxidase positive,does not grow on TCBS agar,has the ability to decarboxylate lysine and ornithine but cannot utilize arginine,and would have the following colonial characteristics on sheep blood agar and MacConkey agar?

A)b-Hemolytic and is a nonlactose fermenter
B)a-Hemolytic and is a lactose fermenter
C)g-Hemolytic and is a nonlactose fermenter
D)a-Hemolytic and is a nonlactose fermenter

Answer 3

A
The organism is Aeromonas veronii biovar veronii.Most pathogenic strains of Aeromonas are b-hemolytic,except Aeromonas caviae,which is usually nonhemolytic.Both lethal factor (LF)and normalized LF (NLF)are found in this group.

Question 4

The primary habitat for Vibrio spp.is:

A)freshwater.
B)the upper respiratory tract of various mammals.
C)brackish or marine water.
D)the soil and water environment.

Question 5

Transmission of P.shigelloides to humans is by:

A)exposure of disrupted skin and mucosal surfaces to contaminated animal hides.
B)ingestion of contaminated seafood or water.
C)inhalation of contaminated air.
D)close contact with carriers of the organism.

Question 6

Stool specimens suspected of containing which of the following enteric pathogens should be collected and transported only in Cary-Blair medium because buffered glycerol saline is toxic for this bacterium?

A)Vibrio
B)Salmonella
C)Shigella
D)Plesiomonas

Question 7

Colonies growing on modified cefsulodin-irgasan-novobiocin (CIN)agar appear to be either Aeromonas spp.or Yersinia enterocolitica.Which test should be performed to differentiate between these two organisms?

A)String test
B)Sucrose fermentation
C)Glucose fermentation
D)Oxidase

Question 8

The transmission of Vibrio spp.to humans is by:

A)exposure of disrupted skin and mucosal surfaces to contaminated animal hides.
B)ingestion of contaminated seafood or water.
C)inhalation of contaminated air.
D)close contact with carriers of the organism.

Question 9

Profuse watery diarrhea (i.e. ,"rice water stools"),leading to dramatic fluid loss,severe dehydration,and hypotension that frequently leads to death,is the hallmark of which toxin activity?

A)Cholera toxin (CT)
B)Enteric endotoxin
C)Shiga toxin
D)Toxin A

Question 10

The selective medium,thiosulfate citrate bile salts sucrose (TCBS)agar,is especially formulated for isolating what pathogen from stool cultures?

A)Vibrio
B)Salmonella
C)Shigella
D)Plesiomonas

Question 11

To determine the validity of 0% sodium chloride (NaCl)broth,which two organisms should be used for quality control purposes?

A)V.alginolyticus and Vibrio cincinnatiensis
B)P.damsela and Vibrio harveyi
C)Vibrio parahaemolyticus and V.cholerae
D)Vibrio vulnificus and P.damsela

Question 12

Which of the following statements best describes the habitats of Vibrio spp. ,Aeromonas spp. ,Plesiomonas shigelloides,and Chromobacterium violaceum?

A)Habitats are limited to the upper respiratory tract of various mammals.
B)Habitats are limited to the gastrointestinal tract.
C)Habitats are mostly soil and water environment.
D)Habitats are limited mostly to soil.

Question 13

Which of the following species of Aeromonas is oxidase-positive,sucrose-positive,and can decarboxylate ornithine?

A)A.caviae
B)Allium schubertii
C)Aeromonas hydrophila
D)A.veronii biovar veronii

Question 14

The reagent used in the "string test" is:

A)bile solubility.
B)sodium deoxycholate.
C)bile esculin.
D)0/129 (2,4-diamino-6,7-diisopropylpteridine).

Question 15

V.cholerae and Vibrio alginolyticus appear what color on TCBS agar?

A)Green
B)Black
C)Yellow
D)Blue

Question 16

Which organism appears green on TCBS agar and is halophilic?

A)V.cholerae
B)V.harveyi
C)Vibrio fluvialis
D)V.vulnificus

Question 17

The drug of choice to treat patients with V.cholerae is:

A)tetracycline.
B)ceftazidime.
C)imipenem.
D)aztreonam.

Question 18

A vibriostatic test using 0/129 (2,4-diamino-6,7-diisopropylpteridine)-impregnated disks differentiates vibrio cells,which are susceptible,and _________,which are resistant.

A)Enterobacteriaceae
B)Plesiomonas spp.
C)aeromonads
D)Chromobacterium spp.

Question 19

V.cholerae and Photobacterium damsela are used to perform quality control on TCBS agar.After overnight incubation,no growth is observed.What is the next course of action?

A)Reinoculate the TCBS agar,and incubate for 36 hours.
B)Check the pH to ensure that it is 8.6.
C)Reincubate the plates for another 24 hours.
D)These two organisms are poor choices for quality control on TCBS agar.

Question 20

Transmission of Aeromonas spp.to humans is by:

A)exposure of disrupted skin and mucosal surfaces to contaminated animal hides.
B)ingestion of contaminated seafood or water.
C)inhalation of contaminated air.
D)close contact with carriers of the organism.