[Resistance to amoxicillin and amoxicillin-clavulanic acid combination of 231 clinical strains of Escherichia coli, isolated in 1992 at the Cochin Hospital].

Among 231 clinical strains of Escherichia coli tested during may 1992, 89 isolates (38.5%) were resistant to beta-lactams. The resistant strains were principally recovered from urinary and genital specimen from medicine and surgical departments. MICs of beta-lactams were determined alone or combined with clavulanic acid, and beta-lactamases were identified by isoelectric point characterization and by enzymatic inhibition tests. Among the resistant strains, 92.1% were secreting a penicillinase and 6.7% a cephalosporinase. No extended-spectrum beta-lactamase was observed. 85.5% of penicillinases were TEM-1 enzymes, 4.9% SHV-1 beta-lactamase, 1.1% OXA-1 beta-lactamase and 8.5%, 7 strains, were IRT beta-lactamases (formerly called TRI). For 24 clinical E. coli strains, the MICs values were > or = 32 mg/l for amoxicillin plus clavulanic acid. The 7 IRT beta-lactamases showed the highest MICs, 256 to 4096 mg/l. Four of them exhibited a beta-lactamase of pI 5.4 and 3 a beta-lactamase of pI 5.2. The IRT beta-lactamases represent 3% of all the Escherichia coli strains. This frequency is comparable or lower than the values reported by other studies conducted between 1992 and 1994.