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Microbiology: HARR Ch. 7.2: Enterobacteriaceae

Terms in this set (51)

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

(The family Enterobacteriaceae consists of more than 100 species and represents the most commonly encountered isolates in clinical specimens. All Enterobacteriaceae ferment glucose and are oxidase negative and nonsporulating. Most Enterobacteriaceae are motile, but the genera Shigella and Klebsiella are not.)
1. Biochemically, the Enterobacteriaceae are gram-negative rods that:
A. Ferment glucose, reduce nitrate to nitrite, and are oxidase negative
B. Ferment glucose, produce indophenol oxidase, and form gas
C. Ferment lactose and reduce nitrite to nitrogen gas
D. Ferment lactose and produce indophenol oxidase
B. Shigella spp. from some strains of Escherichia coli

(The ONPG test detects β-galactosidase activity and is most useful in distinguishing late lactose fermenters from lactose nonfermenters. Some strains of E. coli are slow lactose fermenters and may be confused with Shigella spp., which do not ferment lactose. E. coli are ONPG positive while Shigella spp. are ONPG negative.)
2. The ortho-nitrophenyl-β-galactopyranoside (ONPG) test is most useful when differentiating:
A. Salmonella spp. from Pseudomonas spp.
B. Shigella spp. from some strains of Escherichia coli
C. Klebsiella spp. from Enterobacter spp.
D. Proteus vulgaris from Salmonella spp.
A. Acetoin

(Acetoin or carbinol, an end product of glucose fermentation, is converted to diacetyl after the addition of the VP reagents (α-naphthol and 40% potassium hydroxide [KOH]). Diacetyl is seen as a red- to pink-colored complex.)
3. The Voges-Proskauer (VP) test detects which end product of glucose fermentation?
A. Acetoin
B. Nitrite
C. Acetic acid
D. Hydrogen sulfide
D. 4.5

(Both MR and VP tests detect acid production from the fermentation of glucose. However, a positive MR test denotes a more complete catabolism of glucose to highly acidic end products such as formate and acetate than occurs with organisms that are VP positive only (e.g., Klebsiella pneumoniae).)
4. At which pH does the methyl red (MR) test become positive?
A. 7.0
B. 6.5
C. 6.0
D. 4.5
A. Blue color in the medium after 24 hours of incubation at 35°C
5. A positive Simmons citrate test is seen as a:
A. Blue color in the medium after 24 hours of incubation at 35°C
B. Red color in the medium after 18 hours of incubation at 35°C
C. Yellow color in the medium after 24 hours of incubation at 35°C
D. Green color in the medium after 18 hours of incubation at 35°C
B. Ammonium carbonate
6. In the test for urease production, ammonia reacts to form which product?
A. Ammonium citrate
B. Ammonium carbonate
C. Ammonium oxalate
D. Ammonium nitrate
A. p-Dimethylaminobenzaldehyde

(The indole test detects the conversion of tryptophan (present in the media) to indole by
the enzyme tryptophanase. Indole is detected
by the reaction with the aldehyde group of p-dimethylaminobenzaldehyde (the active reagent in Kovac's and Ehrlich's reagents) in acid, forming a red complex.)
7. Which of the following reagents is added to detect the production of indole?
A. p-Dimethylaminobenzaldehyde
B. Bromcresol purple
C. Methyl red
D. Cytochrome oxidase
D. Amines
8. Decarboxylation of the amino acids lysine, ornithine, and arginine results in the formation of:
A. Ammonia
B. Urea
C. CO2
D. Amines
C. Salmonella spp.
9. Lysine iron agar (LIA) showing a purple slant and a blackened butt indicates:
A. E. coli
B. Citrobacter spp.
C. Salmonella spp.
D. Proteus spp.
C. Ornithine decarboxylase

(Putrescine is the amine product of the decarboxylation of ornithine.)
10. Putrescine is an alkaline amine product of which bacterial enzyme?
A. Arginine decarboxylase
B. Phenylalanine deaminase
C. Ornithine decarboxylase
D. Lysine decarboxylase
B. Morganella, Providencia, and Proteus
11. Which genera are positive for phenylalanine deaminase?
A. Enterobacter, Escherichia, and Salmonella
B. Morganella, Providencia, and Proteus
C. Klebsiella and Enterobacter
D. Proteus, Escherichia, and Shigella
C. Use of sucrose in the medium
12. Kligler iron agar (KIA) differs from triple-sugar iron agar (TSI) in the:
A. Ratio of lactose to glucose
B. Ability to detect H2S production
C. Use of sucrose in the medium
D. Color reaction denoting production of acid
C. Salmonella subgroups 2, 3 (the former Arizona)
13. The malonate test is most useful in differentiating which members of the Enterobacteriaceae?
A. Shigella
B. Proteus
C. Salmonella subgroups 2, 3 (the former Arizona)
D. Serratia
B. Escherichia, Salmonella, Shigella, and Yersinia
14. Which genera of the Enterobacteriaceae are known to cause diarrhea and are considered enteric pathogens?
A. Enterobacter, Klebsiella, Providencia, and Proteus
B. Escherichia, Salmonella, Shigella, and Yersinia
C. Pseudomonas, Moraxella, Acinetobacter, and Aeromonas
D. Enterobacter, Citrobacter, and Morganella
A. Sorbitol (fermentation)
15. 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?
A. Sorbitol (fermentation)
B. Mannitol (oxidation)
C. Raffinose (fermentation)
D. Sucrose (fermentation)
A. E. coli

(Serological confirmation of Shigella isolates is based upon O antigen typing. If a suspected Shigella spp.
is serologically typed with polyvalent sera before it has been correctly identified biochemically, a false-positive confirmation may occur with an isolate that is E. coli (i.e., anaerogenic non-gas-producing, lactose-negative or delayed, and nonmotile
strains). These strains were formerly known as the Alkalescens-Dispar serotype.)
16. Care must be taken when identifying biochemical isolates of Shigella because serological cross reactions occur with:
A. E. coli
B. Salmonella spp.
C. Pseudomonas spp.
D. Proteus spp.
D. S. sonnei
17. Which species of Shigella is most commonly associated with diarrheal disease in the United States?
A. S. dysenteriae
B. S. flexneri
C. S. boydii
D. S. sonnei
B. Lactose, indole, ONPG, and motility
18. Which of the following tests best differentiates Shigella species from E. coli?
A. Hydrogen sulfide, VP, citrate, and urease
B. Lactose, indole, ONPG, and motility
C. Hydrogen sulfide, MR, citrate, and urease D. Gas, citrate, and VP
A. Shigella, Klebsiella, and Yersinia
19. Which genera of Enterobacteriaceae are usually nonmotile at 36°C?
A. Shigella, Klebsiella, and Yersinia
B. Escherichia, Edwardsiella, and Enterobacter
C. Proteus, Providencia, and Salmonella
D. Serratia, Morganella, and Hafnia
A. Campylobacter spp.

(Shigella spp. and Campylobacter spp. are both causes of diarrhea, abdominal pain, fever, and sometimes vomiting. Blood is present in the stools of patients infected with Shigella as a result of invasion and penetration of the bowel. Young children may also exhibit bloody stools when infected with Campylobacter.)
20. 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:
A. Campylobacter spp.
B. Salmonella spp.
C. Proteus spp.
D. Yersinia spp.
D. Y. enterocolitica
21. Cold enrichment of feces (incubation at 4°C) in phosphate-buffered saline prior to subculture onto enteric media enhances the recovery of:
A. Enterotoxigenic E. coli
B. Salmonella paratyphi
C. Hafnia alvei
D. Y. enterocolitica
D. Indole, oxidase, MacConkey, and blood agar plates
22. Which group of tests, along with colonial morphology on primary media, aids most in the rapid identification of the Enterobacteriaceae?
A. MR and VP, urease, and blood agar plate
B. Phenylalanine deaminase, urease, and CDC agar plate
C. Bacitracin, β-lactamase, and MacConkey agar plate
D. Indole, oxidase, MacConkey, and blood agar plates
A. Salmonella, Shigella, Yersinia, Campylobacter, and Staphylococcus aureus
23. A routine, complete stool culture procedure should include media for the isolation of E. coli O157:H7 as well as:
A. Salmonella, Shigella, Yersinia, Campylobacter, and Staphylococcus aureus
B. Vibrio cholerae, Brucella, and Yersinia spp.
C. S. aureus, group B streptococci, and group D streptococci
D. Clostridium difficile, Clostridium perfringens, and Yersinia spp.
A. Motility, urease, and phenylalanine deaminase


(Morganella and Proteus spp. are motile, produce urease, and deaminate phenylalanine.)
24. Which group of tests best identifies the Morganella and Proteus genera?
A. Motility, urease, and phenylalanine deaminase
B. Malonate, glucose fermentation, and deoxyribonuclease (DNase)
C. Indole, oxidase, MR, and VP
D. Indole, citrate, and urease
B. Hydrogen sulfide (H2S) production, sucrose
fermentation, indole, and VP
25. Which group of tests best differentiates Enterobacter aerogenes from Edwardsiella tarda?
A. Motility, citrate, and urease
B. Hydrogen sulfide (H2S) production, sucrose
fermentation, indole, and VP
C. Lysine decarboxylase, urease, and arginine dihydrolase
D. Motility, H2S production, and DNase
A. Yellow pigmentation and negative sorbitol fermentation
26. Enterobacter sakazakii can best be differentiated from Enterobacter cloacae by which of the following characteristics?
A. Yellow pigmentation and negative sorbitol fermentation
B. Pink pigmentation and positive arginine dihydrolase
C. Yellow pigmentation and positive urease
D. H2S production on TSI
D. Negative DNase
27. Members of the genus Cedecea are best differentiated from Serratia spp. by which test result?
A. Positive motility
B. Positive urease
C. Positive phenylalanine deaminase
D. Negative DNase
B. Citrobacter freundii


(Biochemical differentiation is essential because Citrobacter isolates may give a false-positive agglutination test with Salmonella grouping
sera. C. freundii strains, like Salmonella spp., are usually H2S producers and may be confused with Salmonella spp. unless the proper biochemical tests are utilized. C. freundii and Salmonella spp. are adonitol, indole, and malonate negative. However, C. freundii is KCN positive, whereas Salmonella spp. are KCN negative.)
28. Which of the following organisms is often confused with the Salmonella species biochemically and on plated media?
A. E. coli
B. Citrobacter freundii
C. Enterobacter cloacae
D. Shigella dysenteriae
B. Morganella spp.
29. 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:
A. Edwardsiella spp.
B. Morganella spp.
C. Ewingella spp.
D. Shigella spp.
D. Indole
30. Which single test best separates Klebsiella oxytoca from K. pneumoniae?
A. Urease
B. Sucrose
C. Citrate
D. Indole
B. Proteus spp.


(Proteus spp. are urease positive as are approximately 70% of Y. enterocolitica isolates. Both organisms are lactose negative and motile. However, Yersinia is motile at 22°C and not at 35°C (demonstrated using motility media).)
31. Which of the following organisms, found in normal fecal flora, may be mistaken biochemically for the genus Yersinia?
A. Klebsiella spp.
B. Proteus spp.
C. E. coli
D. Enterobacter spp.
D. Pathogenic E. coli can be lactose positive or lactose negative
32. 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?
A. Most Shigella strains are lactose positive
B. Most Salmonella strains are maltose negative
C. Most Proteus spp. are lactose negative
D. Pathogenic E. coli can be lactose positive or lactose negative
C. MacConkey agar
33. Which agar that is used for routine stool cultures is the medium of choice for the isolation of Yersinia strains from stool specimens?
A. Salmonella-Shigella agar
B. Hektoen enteric agar
C. MacConkey agar
D. CNA agar
A. C. freundii strains


(C. freundii and Salmonella spp. are H2S positive and indole, VP, and phenylalanine deaminase negative. Biochemical characteristics that help to differentiate C. freundii from Salmonella include lactose fermentation (50% of C. freundii are lactose positive, whereas 100% of Salmonella are lactose negative) and urease production (70% of Citrobacter are positive and greater than 99% of Salmonella are negative).)
34. Which organism is sometimes mistaken for Salmonella and will agglutinate in Salmonella polyvalent antiserum?
A. C. freundii strains
B. Proteus mirabilis strains
C. S. sonnei strains
D. E. coli
A. Shigella spp.
35. 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
The most likely identification is:
A. Shigella spp.
B. Salmonella spp.
C. Proteus spp.
D. E. coli
D. E. coli

(Enterobacteriaceae are grouped according to their ability to ferment lactose, a β-galactoside. Salmonella, Shigella, Proteus, Providencia, and Morganella are usually lactose nonfermenters.)
36. Which of the following organisms are generally positive for β- galactosidase?
A. Salmonella spp.
B. Shigella spp.
C. Proteus spp.
D. E. coli
D. O, Vi, and H antigens

(The Kaufmann-White schema groups the salmonellae on the basis of the somatic O (heat-stable) antigens and subdivides them into serotypes based on their flagellar H (heat-labile) antigens. The Vi (or K) antigen is a capsular polysaccharide that may be removed by heating. There are over 2,200 serotypes of Salmonella.)
37. In the Kauffmann-White schema, the combined antigens used for serological identification of the Salmonella spp. are:
A. O antigens
B. H antigens
C. Vi and H antigens
D. O, Vi, and H antigens
A. Aminoglycosides, trimethoprim-sulfamethoxazole,
third-generation cephalosporins
38. The drugs of choice for treatment of infections with Enterobacteriaceae are:
A. Aminoglycosides, trimethoprim-sulfamethoxazole,
third-generation cephalosporins
B. Ampicillin and nalidixic acid
C. Streptomycin and isoniazid
D. Chloramphenicol, ampicillin, and colistin
B. E. coli

( Strains of E. coli that produce one or both of the Shiga-like toxins (SLT I and SLT II) can cause bloody diarrhea (hemorrhagic colitis). In the United States, E. coli strain O157:H7 is the serotype most often associated with hemorrhagic colitis.)
39. The Shiga-like toxin (verotoxin) is produced mainly by which Enterobacteriaceae?
A. Klebsiella pneumoniae
B. E. coli
C. Salmonella typhimurium
D. Enterobacter cloacae
A. New Mexico, Arizona, and California
40. Infections caused by Yersinia pestis are rare in the United States. Those cases that do occur are most frequently located in which region?
A. New Mexico, Arizona, and California
B. Alaska, Oregon, and Utah
C. North and South Carolina and Virginia
D. Ohio, Michigan, and Indiana
D. Klebsiella pneumoniae
41. A leg culture from a nursing home patient grew gram-negative rods on MacConkey agar as pink to dark pink oxidase-negative colonies. Given the following results, which is the most likely organism?
Antibiotic susceptibility: resistant to carbenicillin and ampicillin
A. Serratia marcescens
B. Proteus vulgaris
C. Enterobacter cloacae
D. Klebsiella pneumoniae
D. E. coli
42. Four blood cultures were taken over a 24-hour period from a 20-year-old woman with severe diarrhea. The cultures grew motile (room temperature), gram-negative rods. A urine specimen obtained by catheterization also showed gram-negative rods, 100,000 col/mL. Given the following results, which is the most likely organism?

A. Proteus vulgaris
B. Salmonella typhi
C. Yersinia enterocolitica
D. E. coli
A. TSI, motility, indole, urease, Shigella typing with polyvalent sera
43. A stool culture from a 30-year-old man suffering from bloody mucoid diarrhea gave the following results on differential enteric media:
MacConkey agar = clear colonies;
XLD agar = clear colonies;
Hektoen agar = green colonies; Salmonella-Shigella agar = small, clear
Which tests are most appropriate for identification of this enteric pathogen?
A. TSI, motility, indole, urease, Shigella typing with
polyvalent sera
B. TSI, motility, indole, lysine, Salmonella typing with polyvalent sera
C. TSI, indole, MR, VP, citrate
D. TSI, indole, MR, and urease
B. Serratia marcescens


(S. marcescens has been implicated in numerous nosocomial infections and is recognized as an important pathogen with invasive properties. Gelatin hydrolysis and DNase are positive for both the Proteus spp. and Serratia, but the negative urease and phenylalanine deaminase are differential. E. cloacae does not produce DNase, gelatinase, or lysine decarboxylase.)
44. A leg-wound culture from a hospitalized 70-year-old diabetic man grew motile, lactose-negative colonies on MacConkey agar. Given the following biochemical reactions at 24 hours, what is the most probable organism?

A. Proteus vulgaris
B. Serratia marcescens
C. Proteus mirabilis
D. Enterobacter cloacae
A. Proteus vulgaris

(Although P. mirabilis is more frequently recovered from patients with urinary tract infections, P. vulgaris is commonly recovered from immunosuppressed patients. P. mirabilis is indole negative and ornithine decarboxylase positive but otherwise is very similar to P. vulgaris.)
45. Three blood cultures taken from a 30-year-old cancer patient receiving chemotherapy and admitted with a urinary tract infection grew lactose-negative, motile, gram-negative rods prior to antibiotic therapy. Given the following biochemical reactions, which is the most likely organism?

A. Proteus vulgaris
B. Proteus mirabilis
C. Serratia marcescens
D. Klebsiella pneumoniae
C. Yersinia enterocolitica


(Most members of the Enterobacteriaceae family produce detectable growth on MacConkey agar within 24 hours. Yersinia enterocolita produces non-lactose-fermenting colonies on MacConkey agar, salmon-colored colonies on Hektoen agar, and yellow or colorless colonies on XLD agar. If Yersinia enterocolitica is suspected, specialized agar (CIN) is employed. The typical bulls-eye colonies, dark red with a translucent border, can be confused with Aeromonas spp. that appear similarly on CIN agar. To differentiate, an oxidase test must be performed, since Yersinia spp. are oxidase negative and Aeromonas spp. are oxidase positive.)
46. Three consecutive stool cultures from a 25-year-old male patient produced scant normal fecal flora on MacConkey and Hektoen agars. However, colonies on CIN agar (cefsulodin-irgasan-novobiocin) displayed "bulls-eye" colonies after 48 hours incubation. The patient had been suffering from enterocolitis with fever, diarrhea, and abdominal pain for 2 days. What is the most likely identification of this gram-negative rod?
A. E. coli
B. Proteus mirabilis
C. Yersinia enterocolitica
D. Klebsiella pneumoniae
C. E. coli O157:H7


(Inflammation with bleeding of the mucosa of the large intestine (hemorrhagic colitis) is a result of an enterohemorrhagic E. coli (EHEC) infection associated with certain serotypes, such as E. coli O157:H7. The source of the E. coli infection is from ingestion of undercooked ground beef contaminated with fecal matter or drinking raw milk.)
47. A 6-year-old female patient was admitted to the hospital following 2 days of severe diarrhea. Cultures from three consecutive stool samples contained blood and mucus. Patient history revealed a hamburger lunch at a fast-food restaurant 3 days earlier. Which pathogen is most likely responsible for the following results? Growth on:
XLD agar = yellow colonies
HE agar = yellow colonies
Mac agar = light pink and dark pink colonies Mac with sorbitol agar - few dark pink and many
colorless colonies
A. Salmonella spp.
B. Shigella spp.
C. E. coli O157:H7
D. Yersinia enterocolitica
A. Yersinia pestis
48. Following a 2-week camping trip to the Southwest (US), a 65-year-old male patient was hospitalized with a high fever and an inflammatory swelling of the axilla and groin lymph nodes. Several blood cultures were obtained, resulting in growth of gram-negative rods resembling "closed safety pins." The organism grew on MacConkey's agar showing non-lactose-fermenting colonies.
Testing demonstrated a nonmotile rod that was biochemically inert. What is the most likely identification?
A. Yersinia pestis
B. Klebsiella pneumoniae
C. Proteus vulgaris
D. Morganella morganii
B. E. coli O157:H7, Salmonella spp., Shigella spp.
49. The majority of clinical laboratories with a microbiology department should have the capability of serotyping which pathogenic Enterobacteriaceae?
A. Yersinia enterocolitica, Shigella spp.
B. E. coli O157:H7, Salmonella spp., Shigella spp.
C. Yersinia pestis, Salmonella spp.
D. Edwardsiella spp., Salmonella spp.
D. Inhalation of contaminated airborne droplets
50. Direct spread of pneumonic plague disease occurs by which route?
A. Fecal-oral route
B. Rat bite
C. Ingestion of contaminated tissue
D. Inhalation of contaminated airborne droplets
A. E. coli and Klebsiella pneumoniae


(Point mutations occur in most members of the Enterobacteriaceae family that result in production
of a β-lactamase that hydrolyzes broad-spectrum antibiotics such as the cephalosporins as well as penicillin and monobactam antibiotics. These are known as ESBL producers. The most common ESBL organisms are Klebsiella pneumonia and E. coli. ESBL strains are detected by demonstrating their resistance to β-lactam antibiotics.)
51. Which isolates of the Enterobacteriaceae family most commonly produce extended-spectrum β-lactamase (ESBL)?
A. E. coli and Klebsiella pneumoniae
B. Yersinia enterocolitica and Yersinia pestis
C. Morganella morganii and Proteus vulgaris
D. Salmonella typhi and Shigella sonnei
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