Question 1

The gram-negative bacillus that can be described as oxidase-negative, nitrate-positive, and H&#8322;S-positive is&#10;A)E Edwardsiella spp.&#10;B)Shigella vulgaris.&#10;C)Enterobacter aerogenes.&#10;D)Escherichia coli.&#10;E)Shigella sonnei.

Accepted Answer

H₂S-positive is the clue that gives away Edwardsiella sp. in this case. All other bacteria listed are H₂S-negative.

Question 2

Enterotoxigenic and enteroinvasive are terms often linked to which of the following bacterial species?&#10;A)Escherichia coli&#10;B)Salmonella enteritidis&#10;C)Shigella sonnei&#10;D)Yersinia pestis&#10;E)All of the above are correct.

Accepted Answer

Although E. coli is a normal bowel inhabitant, its pathogenic classification is somewhere between that of the overt pathogens and opportunistic organisms. Strains of this species, such as enterotoxigenic E. coli (ETEC), enteroinvasive E. coli (EIEC), and enteroaggregative E. coli (EAEC) express potent toxins and cause serious gastrointestinal infections. Additionally, in the case of enterohemorrhagic E. coli (EHEC), life-threatening systemic disease can result from infection.

Question 3

The serotype O157:H7 of which of the following bacterial species is associated with a serious diarrheal illness with high mortality rates among some populations?&#10;A)Escherichia coli&#10;B)Shigella species&#10;C)Salmonella species&#10;D)Vibrio species

Accepted Answer

The serotype O157:H7 of Escherichia coli is associated with a serious diarrheal illness with high mortality rates among some populations.

Question 4

MacConkey-sorbitol agar is useful for detecting pathogenic strains of&#10;A)Escherichia coli.&#10;B)Shigella species.&#10;C)Salmonella species.&#10;D)Vibrio species.

Accepted Answer

Sorbitol-negative E. coli can be serotyped using commercially available antisera to determine whether the somatic "O" antigen 157 and the flagellar "H" antigen 7 are present.

Question 5

The gram-negative bacillus that can be described as oxidase-negative, nitrate-positive, indole-negative, citrate-positive, methyl red-positive, urease-negative, H&#8322;S-positive is&#10;A)Klebsiella pneumoniae.&#10;B)Proteus vulgaris.&#10;C)Salmonella enteritidis.&#10;D)Escherichia coli.&#10;E)Shigella sonnei.

Accepted Answer

H₂S-positive is the clue that gives away Salmonella sp. in this case. All other bacteria listed are negative.

Question 6

Acid slant, acid butt, no H&#8322;S&#10;A)Salmonella species&#10;B)Escherichia coli&#10;C)Proteus species&#10;D)Pseudomonas species

Accepted Answer

Biochemical profiles obtained with triple sugar iron (TSI) agar are often used to presumptively identify enteric pathogens. Organisms that exhibit the profiles listed require further biochemical profiling and, in the case of Salmonella spp. and Shigella spp., serotyping to establish a definitive identification.

Question 7

Which of the following bacteria are etiologic agents of foodborne gastroenteritis in the United States?&#10;A)Shigella species&#10;B)Salmonella species&#10;C)Yersinia enterocolitica&#10;D)Escherichia coli&#10;E)All of the above are correct.

Accepted Answer

Salmonella spp., Shigella spp., and Yersinia enterocolitica only inhabit the bowel at the time they are causing infection and are acquired by ingestion of contaminated foods or water. This is also the mode of transmission for the various types of E. coli that are known to cause gastrointestinal infections. In contrast, Yersinia pestis is unique among the Enterobacteriaceae that infect humans. This is the only species that is transmitted from animals by the bite of an insect (i.e., flea) vector.

Question 8

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 zoonoses, causing infections in animal populations (Table 22-1). Just as the reservoirs for these organisms vary, so do their modes of transmission to humans.
Most strains of Escherichia coli can be presumptively identified based on which characteristic?

A)Indole positive
B)Citrate positive
C)Methyl red negative
D)Urease positive
E)All of the above are true.

Accepted Answer

In the interests of cost containment, many clinical laboratories use an abbreviated identification scheme for identification of commonly isolated enterics (NCCLS, 35A). E. coli, the most commonly isolated enteric organism, can be identified using a positive spot indole test.

Question 9

The major etiologic agent of urinary tract infections is&#10;A)Escherichia coli.&#10;B)Shigella species.&#10;C)Salmonella species.&#10;D)Vibrio species.

Accepted Answer

For those species that normally colonize humans, infections may result when a patient's own bacterial strains (i.e., endogenous strains) establish infections in a normally sterile body site. These organisms can also be passed from one patient to another. Such infections often depend on the debilitated state of a hospitalized patient and are nosocomially acquired. However, this is not always the case. For example, although Escherichia coli is the most common cause of nosocomial infections, it is also the leading cause of urinary tract infections in nonhospitalized patients.

Question 10

The swarming gram-negative bacillus that can be described as oxidase-negative, nitrate-positive, indole-negative, and H&#8322;S- positive is&#10;A)Proteus aerogenes.&#10;B)Proteus vulgaris.&#10;C)Proteus mirabilis&#10;D)Escherichia coli.

Accepted Answer

In the interests of cost containment, many clinical laboratories use an abbreviated identification scheme for identification of commonly isolated enterics (NCCLS, 35A). A spot indole test can be used to quickly separate swarming Proteae, such as P. mirabilis and P. penneri, which are negative, from the indole-positive P. vulgaris.

Question 11

Alkaline slant, acid butt, no H&#8322;S&#10;A)Salmonella species&#10;B)Escherichia coli&#10;C)Proteus species&#10;D)Pseudomonas species

Accepted Answer

The answer of Alkaline slant, acid butt, no H&#8322;S&#10;A)Salmonella species&#10;B)Escherichia...

Question 12

The first biochemical test that is performed on a gram-negative bacillus growing on MacConkey agar to determine the identification scheme is the&#10;A)catalase test.&#10;B)oxidase test.&#10;C)urease test.&#10;D)indole test.

Accepted Answer

The answer of The first biochemical test that is performed...

Question 13

Not only is this group of gram-negative bacteria considered normal flora of the gastrointestinal tract of humans and animals, but also it 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

Accepted Answer

The answer of Not only is this group of gram-negative...

Question 14

The swarming gram-negative bacillus that can be presumptively identified based on a positive indole test is&#10;A)Klebsiella pneumoniae.&#10;B)Proteus vulgaris.&#10;C)Enterobacter aerogenes.&#10;D)Escherichia coli.&#10;E)Shigella sonnei.

Accepted Answer

The answer of The swarming gram-negative bacillus that can be...

Question 15

Indole production, methyl red, Voges-Proskauer, citrate, urease, oxidase, H&#8322;S production, and gelatin liquefaction are tests historically performed on a&#10;A)gram-negative bacillus.&#10;B)gram-negative coccus.&#10;C)gram-positive coccus.&#10;D)gram-positive bacillus.&#10;E)All of the above are correct.

Accepted Answer

The answer of Indole production, methyl red, Voges-Proskauer, citrate, urease,...

Question 16

Choose the bacterial family that is best described as catalase-positive, oxidase-negative, gram-negative bacilli that are facultative anaerobes and most of which reduce nitrates to nitrites.&#10;A)Enterobacteriaceae&#10;B)Micrococcaceae&#10;C)Pseudomonas&#10;D)Haemophilus

Accepted Answer

The answer of Choose the bacterial family that is best...

Deck 19: Enterobacteriaceae