Laboratory Diagnosis of Enterobacteriaceae

Question 1

Specimen collection, transport, and
processing
A.Isolated from wide variety of clinical
specimens

B.Transport media to ensure isolation
of opportunistic and fastidious
Enterobacteriaceae must be used
such as: (3)

Answer 1

Cary-Blair, Amies, or
Stuarts

Question 2

Direct Microscopic Examination
A. Generally gram-stain is not valuable since Enterobacteriaceae are indistinguishable

B. Gram stain – must be performed on
specimens from in ____ such as ____,
other body fluids or exudates.

C._____ - gram stain is not helpful in the I.D, but may reveal the presence of white blood cells that may help in determining
whether the GI disease is toxin mediated
or an invasive process

Answer 2

sterile sites such as CSF

Stool

Question 3

Culture
A.Enterobacteriaceae are_____ and grow at optimal temperature of_____

B.Some species require lower temperatures (____for Serratia and Yersinia)

C.Routine primary media include: SBA,
CHOC, and selective media such as
MAC

Answer 3

facultative anaerobe

35C-37C

1C – 5C

Question 4

Screening for Stool Cut-lures for Pathogens

A.Fecal specimens should be routinely screened for (3)

Answer 4

Salmonella, Shigella, and EHEC

Question 5

B.Protocol must be in place for Yersinia (______)

Answer 5

such as cold enrichment

Question 6

C._______should be suspected if a lactose-negative, H2S positive colonies are isolated from stool culture.

Answer 6

Salmonella

Question 7

D.Inoculate_____ samples on highly selective media such as HE, XLD in addition to MAC and SMAC

Answer 7

stool

Question 8

E.Enrichment broth (3) – may be used to enhance recovery especially of Salmonella and Shigella

Answer 8

selenite, tetrathionate broth, GN broth

Question 9

The colony examined for its morphology and reaction to lactose is tested for_____

Based on the ability of bacteria to produce Cytochrome C Oxidase that oxidizes the oxidase reagent in the presence of atmospheric oxygen to produce_____ which are purple or dark-blue end products.

Answer 9

Oxidase test.

indophenols

Question 10

Note:

1. Oxidase test is a presumptive
   test that differentiates____ and _____ which are oxidase positive from Enterobacteriaceae which
   are oxidase negative.
2. A gram-negative bacilli primary
   isolated from MAC that tested
   negative for oxidase is presumptively identified as______.
3. An exception to rule #2 is______ which is an oxidase positive member of the family Enterobacteriaceae

Answer 10

Pseudomonas spp. and Vibrio spp.

Enterobacteriaceae

Plesiomonas spp

Question 11

A gram-negative, oxidase
negative isolate on MAC will be
further identified based on a
series of biochemical tests.

Answer 11

CHO utilization patterns

Action towards amino acids
(deamination/decarboxylation)

Other characteristics

Question 12

CHO utilization patterns

Answer 12

Triple Sugar Iron test
MR and VP (IMViC) test
ONPG test for LLF

Question 13

Action towards amino acids
(deamination/decarboxylation)

Answer 13

Lysine Iron Agar test

LOA Reaction using Moeller

Decarboxylase test

Phenylalanine deaminase test

Question 14

Other characteristics

Answer 14

H2S production

Motility, Indole production from tryptophan

Citrate utilization, gelatin hydrolysis, urea hydrolysis

Nitrate reduction