Abstract
Enterohemorrhagic
Escherichia coli
(EHEC) strains isolated from humans, cattle, and food and belonging to serogroups O26 (7 strains), O111 (19 strains), and O157 (70 strains) were examined for susceptibility
to 11 antimicrobial drugs. Fifty-nine strains showing resistance to at least one of the drugs were examined by PCR for the presence of class 1 integrons, which were identified in 17 strains. Integrons were
found more frequently in strains belonging to serogroups O111 and O26 than in the O157 isolates. DNA sequence analysis demonstrated that most of the integrons contained the
aadA1
gene cassette conferring
resistance to streptomycin/spectinomycin, alone or associated with the
drfA1
gene cassette conferring resistance to trimethoprim. One integron, identified in a O157:H7 strain, carried the
aadA2
and
dfrA12
gene cassettes, conferring resistance to streptomycin/spectinomycin and trimethoprim, and the open reading frame F (OrfF) encoding unknown functions. Most of the integrons were carried
by Tn
21
derivative transposons and were transferable by conjugation to an
E. coli
K-12 strain. In conclusion, integrons and antibiotic resistance genes can be frequently found in EHEC strains,
particularly
E. coli
O111 and
E. coli
O26, and their presence could complicate therapeutic trials.