Commonly Isolated Enterobacteriaceae Clinical Microbiology Review 182
KEY REACTIONS
ORGANISM PATHOGENICITY POSITIVE NEGATIVE OTHER
Escherichia coli
Shigella
Edwardsiella tarda
Predominant aerobe in GI tract.
Most common cause of UTI. Green
metallic sheen on EMB. Presumptive
ID: lactose pos, dry colony on Mac-
Conkey, oxidase neg, indole pos.
E. coli O157:H7doesn’t ferment
sorbitol; colorless colonies on SMAC.
Blood, mucus, polys in stool.
Rarely disseminates. Fragile organ-
ism. S. dysenteriaemost severe.
Shigella sonneimost common in
U.S. Serogrouped by O antigens.
Serogroups A, B, C, D. Closely related
to Escherichiaon molecular basis.
Chief reservoirs are reptiles & fresh-
water fish. Infections often involve
aquatic environments. Pos indole
differentiates from Salmonella.
UTI, septicemia, neonatal
sepsis & meningitis,
diarrhea (some)
Dysentery (shigellosis).
Most communicable
of bacterial diarrheas.
Found primarily in
crowded or substandard
conditions, e.g., day-care
centers, jails, prisons
Opportunistic. Bacteremia,
wound infections
Lactose, gas, indole,
MR, motility
MR
Gas, H 2 S, indole, MR,
motility
H 2 S, VP, citrate,
PD, urease
Lactose, gas, H 2 S,
VP, citrate, PD,
urease, motility
Lactose, VP,
citrate, PD, urease
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