Chapter 7.2 - Enterobacteriaceae (HARR)

Ferment glucose, reduce nitrate to nitrite, and are oxidase negative

Biochemically, the Enterobacteriaceae are gram-negative rods that:

Shigella spp. from some strains of Escherichia coli

The ortho-nitrophenyl-β-galactopyranoside (ONPG) test is most useful when differentiating:

Acetoin

The Voges–Proskauer (VP) test detects which end product of glucose fermentation?

4.5

At which pH does the methyl red (MR) test become positive?

Blue color in the medium after 24 hours of incubation at 35°C

A positive Simmons citrate test is seen as a:

Ammonium carbonate

In the test for urease production, ammonia reacts to form which product?

p-Dimethylaminobenzaldehyde

Which of the following reagents is added to detect the production of indole?

Amines

Decarboxylation of the amino acids lysine, ornithine, and arginine results in the formation of:

Salmonella spp.

Lysine iron agar (LIA) showing a purple slant and a blackened butt indicates:

Ornithine decarboxylase

Putrescine is an alkaline amine product of which bacterial enzyme?

Morganella, Providencia, and Proteus

Which genera are positive for phenylalanine deaminase?

Use of sucrose in the medium

Kligler iron agar (KIA) differs from triple-sugar iron agar (TSI) in the:

Salmonella subgroups 2, 3 (the former Arizona)

The malonate test is most useful in differentiating which members of the Enterobacteriaceae?

Escherichia, Salmonella, Shigella, and Yersinia

Which genera of the Enterobacteriaceae are known to cause diarrhea and are considered enteric pathogens?

Sorbitol (fermentation)

An isolate of E. coli recovered from the stool of a patient with severe bloody diarrhea should be tested for which sugar before sending it to a reference laboratory for serotyping?

E. coli

Care must be taken when identifying biochemical isolates of Shigella because serological cross reactions occur with:

S. sonnei

Which species of Shigella is most commonly associated with diarrheal disease in the United States?

Lactose, indole, ONPG, and motility

Which of the following tests best differentiates Shigella species from E. coli?

Shigella, Klebsiella, and Yersinia

Which genera of Enterobacteriaceae are usually nonmotile at 36°C?

Campylobacter spp

Fever, abdominal cramping, watery stools, and fluid and electrolyte loss preceded by bloody stools 2–3 days before is characteristic of shigellosis but may also result from infection with:

Y. enterocolitica

Cold enrichment of feces (incubation at 4°C) in phosphate-buffered saline prior to subculture onto enteric media enhances the recovery of:

Indole, oxidase, MacConkey, and blood agar plates

Which group of tests, along with colonial morphology on primary media, aids most in the rapid identification of the Enterobacteriaceae?

Salmonella, Shigella, Yersinia, Campylobacter, and Staphylococcus aureus

A routine, complete stool culture procedure should include media for the isolation of E. coli O157:H7 as well as:

Motility, urease, and phenylalanine deaminase

Which group of tests best identifies the Morganella and Proteus genera?

Hydrogen sulfide (H2S) production, sucrose fermentation, indole, and VP

Which group of tests best differentiates Enterobacter aerogenes from Edwardsiella tarda?

Yellow pigmentation and negative sorbitol fermentation

Enterobacter sakazakii can best be differentiated from Enterobacter cloacae by which of the following characteristics?

Negative DNase

Members of the genus Cedecea are best differentiated from Serratia spp. by which test result?

Citrobacter freundii

Which of the following organisms is often confused with the Salmonella species biochemically and on plated media?

Morganella spp.

A gram-negative rod is recovered from a catheterized urine sample from a nursing home patient. The lactose-negative isolate tested positive for indole, urease, ornithine decarboxylase, and phenylalanine deaminase and negative for H2S. The most probable identification is:

Indole

Which single test best separates Klebsiella oxytoca from K. pneumoniae?

Proteus spp.

Which of the following organisms, found in normal fecal flora, may be mistaken biochemically for the genus Yersinia?

Pathogenic E. coli can be lactose positive or lactose negative

Why might it be necessary for both pink (lactose-positive) and colorless (lactose-negative) colonies from an initial stool culture on MacConkey agar to be subcultured and tested further for possible pathogens?

MacConkey agar

Which agar that is used for routine stool cultures is the medium of choice for the isolation of Yersinia strains from stool specimens?

C. freundii strains

Which organism is sometimes mistaken for Salmonella and will agglutinate in Salmonella polyvalent antiserum?

Shigella spp.

A bloody stool cultured from a 26-year-old woman after 3 days of severe diarrhea showed the following results at 48 hours after being plated on the following media:

MacConkey agar: little normal flora with many non–lactose-fermenting colonies

Hektoen enteric agar: many blue-green colonies

Campylobacter blood agar and C. difficile agar: no growth

Clear colonies (from MacConkey agar) tested negative for oxidase, indole, urease, motility, and H2S

E. coli

Which of the following organisms are generally positive for β-galactosidase?

O, Vi, and H antigens

In the Kauffmann–White schema, the combined antigens used for serological identification of the Salmonella spp. are:

Aminoglycosides, trimethoprim–sulfamethoxazole, third-generation cephalosporins

The drugs of choice for treatment of infections with Enterobacteriaceae are:

E. coli

The Shiga-like toxin (verotoxin) is produced mainly by which Enterobacteriaceae?

New Mexico, Arizona, and California

Infections caused by Yersinia pestis are rare in the United States. Those cases that do occur are most frequently located in which region?

E. coli O157:H7, Salmonella spp., Shigella spp.

The majority of clinical laboratories with a microbiology department should have the capability of serotyping which pathogenic Enterobacteriaceae?

Inhalation of contaminated airborne droplets

Direct spread of pneumonic plague disease occurs by which route?

E. coli and Klebsiella pneumoniae

Which isolates of the Enterobacteriaceae family most commonly produce extended-spectrum β-lactamase (ESBL)?