Abstract
Fifty isolates of
Escherichia coli
serogroup O111 recovered from humans and various animal species over a 24-year period (1976-1999) were examined for typical virulence-associated factors and susceptibilities
to antimicrobials of human and veterinary significance. Nine H (flagellar) types were identified including nonmotile (
n
= 24), 32 (
n
= 12), negative (
n
= 5), and 56 (
n
= 3).
Thirty-five (70%) isolates possessed at least one Shiga-toxin-producing
E. coli
(STEC)-associated virulence determinants (
eae, stx1, stx2, hlyA
) via PCR analysis. Of these 35 isolates, 20
possessed
eae, stx1,
and
hlyA
genes, whereas three isolates possessed
eae, stx1, stx2,
and
hylA
genes. Multiple antibiotic resistance was observed in 70% of the 50
E. coli
O111 isolates. The majority of isolates displayed resistance to streptomycin, sulfamethoxazole, tetracycline, and kanamycin. Bacterial resistance to ampicillin, gentamicin, chloramphenicol, trimethoprim
and apramycin was also observed. Integrons were identified in 23 (46%) of the
E. coli
isolates assayed, with a 1-kb amplicon being most frequently observed. DNA sequencing of these integrons revealed
the presence of the
aadA
gene, encoding resistance to streptomycin. Two integrons of 1.5 and 2 kb contained the
aadA2
and either
dfrI
or
dfrXII
genes, encoding resistance to
streptomycin and trimethoprim, respectively. Integrons were also identified from isolates dating back to 1982. Isolates were further genetically characterized via ribotyping, which identified 15 distinct
ribogroups, with 62% of isolates clustering into four major ribogroups. Certain riboprint patterns from different animal species, including humans, were observed in isolates spanning the 24-year collection
period, suggesting the dissemination of specialized pathogenic O111 clones.