Question 1

Which organism is oxidase-negative, oxidizes glucose, and is a nonlactose fermenter?

Accepted Answer

The organisms discussed in this chapter are considered together because, except for the Centers for Disease and Control (CDC)group NO-1, they are all oxidase negative and grow on MacConkey agar, as do the Enterobacteriaceae family.However, unlike the Enterobacteriaceae family, which ferments glucose, these organisms either oxidize or do not use glucose.

Question 2

For more serious infections caused by Acinetobacter spp., such as pneumonia or bacteremia, effective treatment may require the use of:

Accepted Answer

For urinary tract infections caused by Acinetobacter spp., single-drug therapy is usually sufficient.In contrast, more serious infections, such as pneumonia or bacteremia, may require the use of a beta-lactam agent in combination with an aminoglycoside antibiotic.

Question 3

A bronchoscopy was performed on a patient who later developed a nosocomial infection as a result of the procedure.The organism recovered from his lung was a nonlactose fermenter that oxidized glucose and maltose, was lysine decarboxylase-positive, and was motile.The organism is most likely which one of the following?

Accepted Answer

The given characteristics are consistent with Stenotrophomonas maltophilia, which is known to cause nosocomial infections and is frequently isolated from patients with compromised immune systems or from medical devices. The organism is a gram-negative nonlactose fermenter that can oxidize glucose and maltose, is lysine decarboxylase-positive, and is motile. None of the other options match this description.

Question 4

Plump coccobacilli that tend to resist alcohol decolorization and may be mistaken for Neisseria spp.are:

Accepted Answer

Acinetobacter spp.are plump coccobacilli that tend to resist alcohol decolorization.The Bordetella spp.are coccobacilli or short rods.S.maltophilia, P.oryzihabitans, and P.luteola are short-to-medium-sized straight rods.

Question 5

The primary drug of choice for infections caused by Stenotrophomonas maltophilia is:

Accepted Answer

S.maltophilia is notoriously resistant to most currently available antimicrobial agents, leaving trimethoprim-sulfamethoxazole as the primary drug of choice for infections caused by this species.Although a few other agents, such as minocycline, ticarcillin and clavulanic acid, and chloramphenicol, often exhibit in vitro activity, clinical experience with these agents is not extensive.Therefore, trimethoprim-sulfamethoxazole remains the drug of choice.

Question 6

The natural habitat of Acinetobacter sp.can best be described as the:

Accepted Answer

These organisms inhabit environmental niches; Acinetobacter spp.and Stenotrophomonas maltophilia are widely distributed in nature and in hospital environments.

Question 7

Which organism may be mistaken for a lactose fermenter on MacConkey agar because of colonies exhibiting a purple hue on the media?

Accepted Answer

Although a nonlactose fermenter, Acinetobacter spp.produces colonies that exhibit a purplish hue and may cause the organism to be mistaken for a lactose fermenter.The other organisms are nonlactose fermenters as well; however, they do not demonstrate this characteristic.

Question 8

Of the following species, which are widely distributed in nature and hospital environments?

Accepted Answer

These organisms inhabit environmental niches; Acinetobacter spp.and S.maltophilia are widely distributed in nature and hospital environments.In contrast, P.luteola, P.oryzihabitans, and the CDC group NO-1 are not commonly encountered in the clinical setting.

Question 9

Differentiation of Stenotrophomonas maltophilia and Burkholderia cepacia is best accomplished by:

Accepted Answer

S.maltophilia can produce biochemical profiles similar to those of B.cepacia, but a negative oxidase test most often rules out the latter.S.maltophilia also oxidizes maltose faster than glucose and produces a brown pigment on heart infusion agar that contains tyrosine.

Question 10

Which organism is often isolated in the sputum of patients with cystic fibrosis?

Accepted Answer

The role of this organism in human disease is uncertain; however, it is occasionally found in the sputa of patients with cystic fibrosis, but clinical significance in this setting is uncertain.

Quiz 20: Acinetobacter, Stenotrophomonas, and Other Organisms