Enterobacteriaceae

A. General characteristics1. Pathogenic genera: human colonizers or

pathogens

2. Non-pathogenic genera: human colonizers or environmentals

3. Oxidase negative, glucose fermenters, grow on MAC

B. Epidemiology1. Reservoirs

a. Inhabit human GI tractb. Inhabit GI tract of other animalsc. Environmental organismsd. Zoonotic pathogens (cause disease in animals)e. Only present during disease

2. Transmissiona. Endogenous infections from patient’s own strainb. Person to personc. Ingestion of contaminated food or waterd. Vector-borne

C. Pathogenesis and spectrum of disease1. Overt pathogens

a. Salmonella spp.: GI, bacteremia and extraintestinal infections, enteric fever (typhoid fever)

b. Shigella spp.: dysenteryc. Yersinia pestis: “black” plague

2. Opportunistic pathogensa. Citrobacter spp., Enterobacter spp., Klebsiella spp.,

Proteus spp., and Serratia spp.b. can be very pathogenic, but usually only in

immunocompromised

3. Eschericia colia. more pathogenic than opportunists; some strains are

overt pathogensTABLE 25-2

D. Laboratory diagnosis1. Specimen collection, transport, processing

a. No special considerations for these organisms

2. Direct detection methodsa. No specific procedures for routine enterics

3. Culture and identificationa. Media

i. BAP, CAP, Mac all support growth large gray smooth on BAP, CAPTABLE 25-3

ii. CIN agar for selection of Yersiniaiii. Hektoen for Salmonella/Shigellaiv. MacConkey-Sorbitol: E. coli O157 can’t ferment sorbitol

Gram stain of enteric Gram-negative rods

http://www.nirgal.net/life_nano.html

D. Laboratory diagnosis3. Culture and identification

b. Colony appearancei. Swarming of Proteus indole + P. vulgaris, indole – P. mirabilisii. Mucoid Klebsiella

iii. H2S positive Salmonella on Hektoeniv. Serratia makes a red pigmentv. Yersinia red center with clear border on CIN

c. Identificationi. API strips, automated systemsii. TSI slantsiii. Salmonella antisera

http://www.vetmed.wisc.edu/pbs/courses/bact/labmanual/c4klebsiella.html

Enteric gram-negative rods on BAP

E. coli Klebsiella sp.

http://www.vetmed.wisc.edu/pbs/courses/bact/labmanual/c4klebsiella.html

Enteric gram-negative rods on BAP

Proteus sp.

http://www.msu.edu/course/fsc/441/resulex14.html

Hektoen agar

TSI slant

Identification of Salmonella and Shigella

http://www.troybio.com/images/Product_Images_BBL/BBL.htm

CIN agar for the recovery of Yersinia sp.

D. Laboratory diagnosis4. Antimicrobial susceptibility testing and therapy

a. Susceptibility is unpredictable, so testing is warranted for extra-intestinal infectionsb. Treatment of GI disease with antibiotics is controversial

Vibrio, Aeromonas, Plesiomonas

A. General characteristics1. Different from enterics: Oxidase-positive, glucose-

ferm, grow on Mac

B. Epidemiology1. Reservoirs

a. Vibrio: brackish or salt water

b. Aeromonas: various aquatic environments

c. Plesiomonas: fresh water

2. Transmissiona. Vibrio: fecal-oral, exposure to contaminated seafood or

water

b. Aeromonas: exp. to contam food or water; traumatic injury (fish hooks)

c. Plesiomonas: exp to contam food or water; exp to reptiles

C. Pathogenesis and spectrum of disease1. V. cholerae

a. cholera toxin causes mucosal cells to hypersecrete water and electrolytes

b. profuse watery diarrhea, fluid loss, dehydration (rice-water stools: fluid and mucous flecks)

c. somatic O1 and O139 are markers for epidemic/pandemic strains; non O1 or O139 do not produce toxin

2. Non-cholerae vibrioa. specific virulence factors undefinedb. gastroenteritis from seafood, wound infections,

septicemia

3. Aeromonas and Plesiomonasa. virulence factors unclearb. gastroenteritis, wound infections, septicemia

D. Laboratory diagnosis1. Specimen collection, transport, processing

a. no unique requirements except that suspected Vibrio should only be transported in Cary-Blair, because glycerol in buffered glycerol saline is toxic to vibrios

2. Direct detection methodsa. Vibrios: gnr, slightly curvedb. Aeromonas: gnr, straightc. Plesiomonas: gnr, single, pairs, short chains, or long

filaments

http://www2.mf.uni-lj.si/~mil/bakt2/bakt2.htm

Gram stain of Vibrio sp.

D. Laboratory diagnosis3. Culture and identification

a. Mediai. all grow on blood and Macii. may be LFs or NLFsiii. Thiosulfate citrate bile salts sucrose (TCBS); selective

media for vibrio: ferments sucrose and makes yellow colonies on blue-green plate.

b. Colony appearancei. look like gnrs, Aeromonas may be beta-hemeii. all are OXIDASE-POSITIVE; we look for ox+ positive that

are not Pseudomonas

c. Identificationi. API strips or similar

http://idsc.nih.go.jp/idwr/kansen/k01_g1/k01_12/k01_12.html

TCBS agar for the recovery of Vibrio sp.

D. Laboratory diagnosis4. Antimicrobial susceptibility testing and

therapya. Tetracycline or doxy are first line drugs for cholera, but fluid management for this and other orgs in main therapyb. no standardized testing methods for any of these