Bacteriology: 7.2 Enterobacteriaceae

Question 1

Biochemically, the Enterobacteriaceae are gram-negative rods that:

Answer 1

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

Question 2

The family – consists of more than 100 species and represents the most commonly encountered isolates in clinical specimens.

Answer 2

Enterobacteriaceae

Question 3

All Enterobacteriaceae ferment – and are – negative and nonsporulating. Most Enterobacteriaceae are motile, but the genera Shigella and Klebsiella are not.

Answer 3

glucose, oxidase -

Question 4

All Enterobacteriaceae ferment glucose and are oxidase negative and nonsporulating. Most Enterobacteriaceae are motile, but the genera – and –are not.

Answer 4

Shigella and Klebsiella

Question 5

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

Answer 5

Shigella spp. from some strains of Escherichia coli

Question 6

The – test detects β-galactosidase activity and is most useful in distinguishing late lactose fermenters from lactose nonfermenters.

Answer 6

ONPG test

Question 7

Some strains of E. coli are slow lactose fermenters and may be confused with – spp., which do not ferment lactose.

E. coli are ONPG positive while –spp. are ONPG negative.

Answer 7

Shigella

Question 8

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

Answer 8

Acetoin

Question 9

– or – , 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.

Answer 9

Acetoin or carbinol

Question 10

Acetoin or carbinol, an end product of glucose fermentation, is converted to – after the addition of the VP reagents (α-naphthol and 40% potassium hydroxide [KOH]). Diacetyl is seen as a red- to pink-colored complex.

Answer 10

diacetyl

Question 11

Acetoin or carbinol, an end product of glucose fermentation, is converted to diacetyl after the addition of the VP reagents (–). Diacetyl is seen as a red- to pink-colored complex.

Answer 11

α-naphthol and 40% potassium hydroxide [KOH]

Question 12

Diacetyl is seen as a — to —colored complex.

Answer 12

red- to pink

Question 13

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

Answer 13

4.5

Question 14

Both – tests detect acid production from the fermentation of glucose.

Answer 14

MR and VP

Question 15

positive– 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).

Answer 15

MR

Question 16

A positive Simmons citrate test is seen as a

Answer 16

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

Question 17

The – test determines if an organism can utilize citrate as the sole source of carbon. The medium turns blue, indicating the presence of alkaline products such as carbonate. Tubes are incubated a minimum of 24 hours at 35°C with a loose cap before reading.

Answer 17

Simmons citrate test

Question 18

The Simmons citrate test determines if an organism can utilize citrate as the sole source of carbon. The medium turns –, indicating the presence of alkaline products such as carbonate. Tubes are incubated a minimum of 24 hours at 35°C with a loose cap before reading.

Answer 18

blue

Question 19

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

Answer 19

Ammonium carbonate

Question 20

The test for urease production is based on the ability of the colonies to hydrolyze urea in Stuart broth or Christensen agar to form CO2 and ammonia. These products form ammonium carbonate, resulting in alkalinization. This turns the pH indicator (phenol red) – at pH–

Answer 20

pink at pH 8.0

Question 21

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

Answer 21

p-Dimethylaminobenzaldehyde

Question 22

The indole test detects the conversion of tryptophan (present in the media) to indole by the enzyme –.

Answer 22

tryptophanase

Question 23

– 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.

Answer 23

Indole

Question 24

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

Answer 24

Amines

Question 25

Specific decarboxylases split dibasic amino acids (lysine, arginine, and ornithine), forming alkaline amines. These products turn the pH indicators in the medium (cresol red and bromcresol purple) from – to –

Answer 25

yellow to purple

Question 26

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

Answer 26

Salmonella spp.

Question 27

– is used as an aid for the identification of Salmonella species. It contains phenylalanine, lysine, glucose, thiosulfate, ferric ammonium citrate, and bromcresol purple.

Answer 27

LIA

Question 28

Salmonella produce H2S from –. This reduces ferric ammonium citrate, forming ferrous sulfate and causing the butt to blacken.

Answer 28

thiosulfate

Question 29

Salmonella also decarboxylate lysine to produce alkaline amines, giving the slant its purple color and differentiating it from – spp., which are lysine decarboxylase negative.

Answer 29

Citrobacter

Question 30

Putrescine is an alkaline amine product of which bacterial enzyme?

Answer 30

Ornithine decarboxylase

Question 31

– is the amine product of the decarboxylation of ornithine

Answer 31

Putrescine

Question 32

Which genera are positive for phenylalanine deaminase?

Answer 32

Morganella, Providencia, and Proteus

Question 33

Phenylalanine deaminase oxidatively deaminates phenylalanine, forming phenylpyruvic acid. When a solution of ferric chloride is added, the iron reacts with phenylpyruvic acid, forming a —colored complex.

Answer 33

green

Question 34

– is found in the genera Morganella, Providencia, and Proteus and is an excellent test to determine if an organism belongs to this group. Rarely, isolates of Enterobacter may be–positive as well.

Answer 34

Phenylalanine deaminase

Question 35

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

Answer 35

Use of sucrose in the medium

Question 36

Both KIA and TSI contain 10-fold more – than glucose, peptone, and phenol red to detect acid production (turns yellow) and sodium thiosulfate and ferrous ammonium sulfate to detect H2S production.

Answer 36

lactose

Question 37

TSI contains – and KIA does not.

Answer 37

sucrose

Question 38

Organisms fermenting either sucrose or lactose will turn the slant of the agar tube –.

Answer 38

yellow

Question 39

some organisms (e.g., many species of Cedecea, Citrobacter, Edwardsiella, and Serratia) will produce a – slant on TSI but a – slant on KIA.

Answer 39

yellow, red

Question 40

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

Answer 40

Salmonella subgroups 2, 3 (the former Arizona)

Question 41

The – test determines whether an organism can utilize sodium malonate as the sole source of carbon. – is broken down, forming alkaline metabolites that raise the pH of the broth above 7.6.

Answer 41

malonate

Question 42

malonate test:

This causes bromthymol blue to turn from green to –.

Answer 42

deep blue (Prussian blue)

Question 43

malonate test:

E. coli, Shigella, and most Salmonella are malonate negative, whereas – and – (formerly Arizona) subgroups 2, 3a, and 3b are positive. Proteus, Providencia, Serratia, and Yersinia are also malonate negative

Answer 43

Enterobacter and Salmonella

Question 44

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

Answer 44

Escherichia, Salmonella, Shigella, and Yersinia

Question 45

(4) are responsible for the majority of enteric diarrhea cases attributable to the Enterobacteriaceae family.

Answer 45

Escherichia, Salmonella, Shigella, and Yersinia

Question 46

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?

Answer 46

Sorbitol (fermentation)

Question 47

An isolate of E. coli recovered from a stool culture in hemorrhagic colitis can be definitely identified only by –.

Answer 47

serotyping

Question 48

The strain of E. coli responsible for hemorrhagic colitis is – and is usually negative for sorbitol fermentation. Colonies of this strain of E. coli appear colorless on MacConkey agar with sorbitol added.

Answer 48

O157:H7

Question 49

The strain of E. coli responsible for hemorrhagic colitis is O157:H7 and is usually negative for sorbitol fermentation. Colonies of this strain of E. coli appear – on MacConkey agar with sorbitol added.

Answer 49

colorless

Question 50

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

Answer 50

E. coli

Question 51

Serological confirmation of Shigella isolates is based upon – antigen typing.

Answer 51

O antigen

Question 52

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 – serotype.

Answer 52

Alkalescens-Dispar

Question 53

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

Answer 53

S. sonnei

Question 54

The Shigella spp. are lactose – that for the most part are biochemically inert and are classified into serogroups A, B, C, and D as a result of their biochemical similarity.

Answer 54

nonfermenters

Question 55

– is the species most often isolated from diarrhea cases in the United States. It is more active biochemically than the other species owing to ornithine decarboxylase and β-galactosidase activity.

Answer 55

S. sonnei

Question 56

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

Answer 56

Lactose, indole, ONPG, and motility

Question 57

–, positive for lactose, indole, and ONPG are usually motile. Shigella species do not ferment lactose or produce indole, lack β-galactosidase, and are nonmotile.

Answer 57

E. coli

Question 58

E. coli, positive for lactose, indole, and ONPG are usually motile. – species do not ferment lactose or produce indole, lack β-galactosidase, and are nonmotile.

Answer 58

Shigella

Question 59

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

Answer 59

Shigella, Klebsiella, and Yersinia

Question 60

Shigella spp. and Klebsiella spp. are for the most part nonmotile. – can be motile at 22°C but is nonmotile at 36°C.

Answer 60

Yersinia

Question 61

Other members of the Enterobacteriaceae that have been isolated from human specimens and are usually – include Leminorella, Rahnella, and Tatumella.

Answer 61

nonmotile

Question 62

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:

Answer 62

Campylobacter spp.

Question 63

–spp. and –spp. are both causes of diarrhea, abdominal pain, fever, and sometimes vomiting. Blood is present in the stools of patients infected with –as a result of invasion and penetration of the bowel. Young children may also exhibit bloody stools when infected with –.

Answer 63

Shigella spp. and Campylobacter spp

Question 64

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

Answer 64

Y. enterocolitica

Question 65

– is especially useful when specimens contain large numbers of normal flora that are sensitive to prolonged exposure to near-freezing temperature. In addition to Yersinia, the technique has been used to enhance recovery of Listeria monocytogenes from specimens containing other bacteria.

Answer 65

Cold enrichment

Question 66

Cold enrichment : In addition to Yersinia, the technique has been used to enhance recovery of – from specimens containing other bacteria.

Answer 66

Listeria monocytogenes

Question 67

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

Answer 67

Indole, oxidase, MacConkey, and blood agar plates

Question 68

All Enterobacteriaceae are oxidase –.

Answer 68

negative

Question 69

– display a positive indole test, and the colonial morphology on MacConkey agar is distinctive, showing flat, pink (lactose-positive) colonies with a ring of bile precipitation.

Answer 69

E. coli

Question 70

– swarm on blood agar and are indole negative.

Answer 70

Proteus spp.

Question 71

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

Answer 71

Salmonella, Shigella, Yersinia, Campylobacter, and Staphylococcus aureus

Question 72

are usually not included in a routine stool culture. If Vibrio spp. are suspected, a special request should be included.

Answer 72

V. cholerae and C. difficile

Question 73

– culture requires special media (CCFA) that inhibit other anaerobic flora and facultative anaerobic flora and should be requested specifically if symptoms warrant.

Answer 73

C. difficile

Question 74

– agar with – will allow the E. coli O157:H7 to be recovered.

Answer 74

MacConkey agar with sorbitol

Question 75

–spp. can be detected on a regular MacConkey agar plate.

Answer 75

Yersinia

Question 76

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

Answer 76

Motility, urease, and phenylalanine deaminase

Question 77

–and –spp. are motile, produce urease, and deaminate phenylalanine

Answer 77

Morganella and Proteus

Question 78

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

Answer 78

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

Question 79

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

Answer 79

Yellow pigmentation and negative sorbitol fermentation

Question 80

– is called a yellow-pigmented E. cloacae and is best differentiated from E. cloacae by sorbitol fermentation (95% positive for E. cloacae and 0% for E. sakazakii).

Answer 80

E. sakazakii

Question 81

E. sakazakii is called a yellow-pigmented E. cloacae and is best differentiated from E. cloacae by – fermentation (95% positive for E. cloacae and 0% for E. sakazakii).

Answer 81

sorbitol

Question 82

E. cloacae is usually positive for –and –(65% and 75%, respectively) and E. sakazakii is usually negative (1% and
< 20%, respectively). Both species are usually motile and arginine dihydrolase positive.

Answer 82

urease and malonate