Deck 18: Enterobacteriaceae

Question 1

Most strains of Escherichia coli can be presumptively identified on the basis of which characteristic?

A)Spot indole-positive
B)Citrate-positive
C)Methyl red-negative
D)Urease-positive

Answer 1

A
In the interests of cost containment,many clinical laboratories use an abbreviated identification scheme for identifying commonly isolated enteric organisms (Clinical Laboratory Standards Institute [CLSI],35A).E.coli,the most commonly isolated enteric organism,can be identified using a positive spot indole test.

Question 2

In addition to being a group of gram-negative bacteria considered normal flora of the gastrointestinal tract of humans and animals,which one of the following also contains agents of important diseases such as gastroenteritis and enteric fevers,urinary tract infections,and bacterial pneumonia?

A)Neisseriaceae
B)Micrococcaceae
C)Enterococcus
D)Enterobacteriaceae

Answer 2

D
Enterobacteriaceae inhabit a wide variety of niches that include the human gastrointestinal tract,the gastrointestinal tract of other animals,and various environmental sites.Some are agents of zoonosis,causing infections in animal populations.Just as the reservoirs for these organisms vary,so do their modes of transmission to humans.

Question 3

A gram-negative bacillus that is hydrogen sulfide (H₂S)-positive,citrate-positive,spot indole-negative,and associated with gastroenteritis in the United States is most likely:

A)K.pneumoniae.
B)P.vulgaris.
C)Salmonella enteritidis.
D)S.sonnei.

Answer 3

C
H₂S-positive is the clue that gives away Salmonella spp.in this case.Although P.vulgaris is the only other organism that is H₂S-positive,it is spot indole-positive,not negative.

Question 4

MacConkey-sorbitol agar is useful for detecting pathogenic strains of:

A)E.coli.
B)Shigella spp.
C)Salmonella spp.
D)Vibrio spp.

Question 5

Which is correct for the description "alkaline slant,acid butt,no H₂S"?

A)Salmonella spp.
B)E.coli
C)Proteus spp.
D)Pseudomonas spp.

Question 6

If an organism were a glucose and lactose fermenter,the LIA reaction would be:

A)K/A.
B)A/K.
C)A/A.
D)K/K.

Question 7

A green colony with a black center was isolated and presumptively identified as a Salmonella spp.The organism was serotyped with polyvalent antisera;however,the antisera tested negative for all antigens.What is the next course of action?

A)Regrow the organism on sheep blood agar,and serotype again the next day.
B)Make a suspension,and heat to 100°C for 10 minutes.
C)Make a suspension,and place on ice for 30 minutes.
D)Report the organism out as a nontypable Salmonella spp.

Question 8

Of the following bacterial species,which is associated with a serious diarrheal illness with high mortality rates among some populations?

A)E.coli
B)Shigella spp.
C)Salmonella spp.
D)Vibrio spp.

Question 9

A green colony with a black center is isolated on HE agar from a stool specimen.It is most likely which organism?

A)E.coli
B)Salmonella spp.
C)Shigella spp.
D)K.pneumoniae

Question 10

Which of correct for the description "acid slant,acid butt,no H₂S"?

A)Salmonella spp.
B)E.coli
C)Proteus spp.
D)Pseudomonas spp.

Question 11

On MacConkey agar,Serratia spp.would appear:

A)red.
B)colorless.
C)green.
D)yellow.

Question 12

For the most part,all Enterobacteriaceae are positive for which biochemical reactions?

A)Glucose,oxidase,and catalase
B)Glucose,indole,and oxidase
C)Glucose,reduce nitrates to nitrites,and oxidase
D)Glucose,catalase,and reduce nitrates to nitrites

Question 13

A patient bitten by a flea developed a painful bubo at the site of the bite.The drug of choice for this organism is:

A)ampicillin.
B)gentamycin.
C)streptomycin.
D)ciprofloxacin.

Question 14

An organism that appears red with a black center on XLD agar is lactose-_____ and H₂S-_____.

A)positive;positive
B)positive;negative
C)negative;positive
D)negative;negative

Question 15

Enterotoxigenic and enteroinvasive are terms often linked to which of the following bacterial species?

A)E.coli
B)S.enteritidis
C)S.sonnei
D)Yersinia pestis

Question 16

The swarming gram-negative bacillus that can be presumptively identified on the basis of a positive indole test is:

A)Klebsiella pneumoniae.
B)Proteus vulgaris.
C)Enterobacter aerogenes.
D)Shigella sonnei.

Question 17

The major etiologic agent of urinary tract infections is:

A)E.coli.
B)Shigella spp.
C)Salmonella spp.
D)Vibrio spp.

Question 18

E.coli would appear what color on HE agar?

A)Green
B)Green with a black center
C)Yellow
D)Yellow with a black center

Question 19

E.coli can produce a toxin similar to S.dysenteriae and can cause hemorrhagic colitis.What other organ does it affect?

A)Heart
B)Lungs
C)Liver
D)Kidney

Question 20

This organism,belonging to the family Enterobacteriaceae,grows best at 25°C to 30°C.Domestic and wild rats and other animals can carry this organism.What is the medium of choice?

A)MacConkey agar
B)Xylose-lysine-deoxycholate (XLD)agar
C)Cefsulodin-irgasan-novobiocin (CIN)agar
D)Hektoen enteric (HE)agar