Transferable high-level trimethoprim resistance among isolates ofEscherichia colifrom urinary tract infections in Ontario, Canada

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Abstract
SUMMARY: Of 1171 isolates ofEscherichia coliisolated from urine samples at the Public Health Laboratory, Toronto, Ontario, Canada, between May 1990 and December 1991, 120 (10·3%) were resistant to trimethoprim (TMP), cotrimoxazole (TMP/SMX), sulfamethoxazole (SMX) and other antimicrobial agents; 110 of the 120 isolates (91·7%) were resistant to four or more agents. The majority of resistant isolates (91·7%) exhibited high-level resistance (MIC > 1000 mg/L) to TMP. The MIC of TMP/SMX for all 120 isolates was > 2·0/38·0 mg/L and for SMX > 1024 mg/L. High-level resistances were also present among the β-lactam antimicrobials with MICs ranging from 16- > 256 mg/L. Forty-three of 120 TMP-resistant (35·8%) isolates conjugally transferred TMP-resistance toE. coliK-12. Co-transfer of several other resistances was observed. SMX cotransferred from 86% of the 43 donors and β-lactams together with SMX cotransferred from 70%. Nalidixic acid resistance was present among 22 (18·3%) of the 120 resistant isolates, however, nalidixic acid resistance was not transferred toE. coliK-12.