Enterobacteriaceae
A. General characteristics
1. Pathogenic genera: human colonizers or
pathogens
2. Non-pathogenic genera: human colonizers
or environmentals
3. Oxidase negative, glucose fermenters,
grow on MAC
B. Epidemiology
1. Reservoirs
a. Inhabit human GI tract
b. Inhabit GI tract of other animals
c. Environmental organisms
d. Zoonotic pathogens (cause disease in animals)
e. Only present during disease
2. Transmission
a. Endogenous infections from patient’s own strain
b. Person to person
c. Ingestion of contaminated food or water
d. Vector-borne
C. Pathogenesis and spectrum of disease
1. Overt pathogens
a. Salmonella spp.: GI, bacteremia and extraintestinal
infections, enteric fever (typhoid fever)
b. Shigella spp.: dysentery
c. Yersinia pestis: “black” plague
2. Opportunistic pathogens
a. Citrobacter spp., Enterobacter spp., Klebsiella spp.,
Proteus spp., and Serratia spp.
b. can be very pathogenic, but usually only in
immunocompromised
3. Eschericia coli
a. more pathogenic than opportunists; some strains are
overt pathogens
TABLE 25-2
D. Laboratory diagnosis
1. Specimen collection, transport, processing
a. No special considerations for these organisms
2. Direct detection methods
a. No specific procedures for routine enterics
3. Culture and identification
a. Media
i. BAP, CAP, Mac all support growth
large gray smooth on BAP, CAP
TABLE 25-3
ii. CIN agar for selection of Yersinia
iii. Hektoen for Salmonella/Shigella
iv. 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 diagnosis
3. Culture and identification
b. Colony appearance
i. Swarming of Proteus
indole + P. vulgaris, indole – P. mirabilis
ii. Mucoid Klebsiella
iii. H2S positive Salmonella on Hektoen
iv. Serratia makes a red pigment
v. Yersinia red center with clear border on CIN
c. Identification
i. API strips, automated systems
ii. TSI slants
iii. Salmonella antisera
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.vetmed.wisc.edu/pbs/courses/bact/labmanual/c4klebsiella.html
Identification of Salmonella and Shigella
TSI slant
Hektoen agar
http://www.msu.edu/course/fsc/441/resulex14.html
CIN agar for the recovery of Yersinia sp.
http://www.troybio.com/images/Product_Images_BBL/BBL.htm
D. Laboratory diagnosis
4. Antimicrobial susceptibility testing and therapy
a. Susceptibility is unpredictable, so testing is warranted
for extra-intestinal infections
b. Treatment of GI disease with antibiotics is
controversial
Vibrio, Aeromonas, Plesiomonas
A. General characteristics
1. Different from enterics: Oxidase-positive, glucoseferm, grow on Mac
B. Epidemiology
1. Reservoirs
a. Vibrio: brackish or salt water
b. Aeromonas: various aquatic environments
c. Plesiomonas: fresh water
2. Transmission
a. 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 disease
1. V. cholerae
a. cholera toxin causes mucosal cells to hypersecrete
water and electrolytes
b. profuse watery diarrhea, fluid loss, dehydration (ricewater 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 vibrio
a. specific virulence factors undefined
b. gastroenteritis from seafood, wound infections,
septicemia
3. Aeromonas and Plesiomonas
a. virulence factors unclear
b. gastroenteritis, wound infections, septicemia
D. Laboratory diagnosis
1. 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 methods
a. Vibrios: gnr, slightly curved
b. Aeromonas: gnr, straight
c. Plesiomonas: gnr, single, pairs, short chains, or long
filaments
Gram stain of Vibrio sp.
http://www2.mf.uni-lj.si/~mil/bakt2/bakt2.htm
D. Laboratory diagnosis
3. Culture and identification
a. Media
i. all grow on blood and Mac
ii. may be LFs or NLFs
iii. Thiosulfate citrate bile salts sucrose (TCBS); selective
media for vibrio: ferments sucrose and makes yellow
colonies on blue-green plate.
b. Colony appearance
i. look like gnrs, Aeromonas may be beta-heme
ii. all are OXIDASE-POSITIVE; we look for ox+ positive that
are not Pseudomonas
c. Identification
i. API strips or similar
TCBS agar for the recovery of Vibrio sp.
http://idsc.nih.go.jp/idwr/kansen/k01_g1/k01_12/k01_12.html
D. Laboratory diagnosis
4. Antimicrobial susceptibility testing and therapy
a. Tetracycline or doxy are first line drugs for cholera, but
fluid management for this and other orgs in main therapy
b. no standardized testing methods for any of these