Quiz 7: Enterobacterales: NLFs and SLFs

Which genera are non-motile at 35C?

Shigella, Klebsiella, and Yersinia

Describe the ONPG test.

Positive for isolates that ferment lactose but lack permease

The Shigella species most often isolated in the US belongs to this serogroup

D

Which test best differentiates S. sonnei from other Shigella spp.?

ONPG

Which organism is most commonly associated with infantile diarrhea and traveler’s diarrhea due to the production of enterotoxins?

E. coli

This disease is characterized initially by fever, bacteremia, infection of the reticuloendothelial system with “rose spots” and diarrhea.

Typhoid fever

This organism possesses the Vi capsular antigen

Salmonella ser. Typhimurium

Which antigens are used to serotype Salmonella isolates?

O, H, and Vi antigens

Which mechanism is responsible for hemolytic uremic syndrome?

Production of Stx toxin

Which medium should be inoculated to screen for the organism associated with hemorrhagic colitis and HUS?

Sorbitol-MacConkey

Which test will best differentiate Proteus mirabilis from Proteus vulgaris?

Indole

Based on IMViC results, this organism could be called H2S positive E. coli?

Edwardsiella tarda

Which of the following is not considered confirmatory for EHEC?

Clear colonies on SMAC

Which test best differentiates Salmonella enterica and Citrobacter freundii?

LDC

Culture of a bloody, mucous stool collected from a 26yo female after 2 days of severe diarrhea have the following results @ 18hrs incubation

MAC = Clear colonies

HEK = Green colonies

Clear colonies from MAC is negative for ONPG, Indole, Urease, H2S, Motility.

What is the most likely ID?

Shigella boydii

A stool culture has colorless colonies on MAC and colorless colonies with black centers on HEK. Biochemical results on API20E @ 18hr incubation are:

H2S (+) Tryptophan Deaminase (-)

ONPG (-) Indole (-)

Citrate (+) Urease (-)

What is the most likely ID?

Salmonella enterica

A stool isolate is biochemically identified as Salmonella, but fails to agglutinate in the antisera for Salmonella serogrouping. What should be the next step?

Boil a suspension of the isolate for 15 minutes and retest with antisera

A leg wound culture from a hospitalized 70yo diabetic male grew NLF colonies on MAC @ 18hrs incubation. Phenotypic test results @ 18hrs incubation are:

Phenylalanine deaminase (-) ONPG (+)

ODC (+) Indole (-)

LDC (+) Arginine dihydrolase (-)

VP (+) Gelatinase (+)

Urease (-) Motility (+)

What is the most probable organism isolated?

Serratia marcescens

An isolate from a urine culture from a nursing home patient is colorless on MAC. Phenotypic test results on the isolate @ 18hr incubation are:

PDA (+)

H2S (-) Indole (+)

ODC (+) Citrate (-)

Morganella morganii

A 10yo boy was admitted in the ED with a diagnosis of appendicitis. During surgery, the appendix appeared normal, but an enlarged lymph node was removed and sent to the lab for culture. Colorless colonies on MAC are urease positive, indole-positive, and non-motile @37C. This scenario suggests the etiologic agent is most likely

Yersinia enterocolitica

A urine culture has colorless colonies on MAC that swam on SBA. Phenotypic test results are:

PDA (+) Citrate (+)

LDC (-) Urease (+)

ODC (+) Indole (-)

What is the most probable ID of this organism?

Proteus mirabilis

A stool culture from a 3yo has 2 colorless colony types on MAC and pink colonies on SMAC. On HEK, isolate #1 retains the original color of the medium and isolate #2 has black centers. The following screen tests for enteric pathogens are performed and the results are:

Test Isolate #1 Isolate #2

Urease (-) (+)

Indole (-) (-)

The MLS performed additional biochemical testing that confirmed the identification of the isolates. What should the MLS do next?

Shigella serogrouping