[Sensitivity to clavulanic acid of Escherichia coli isolated at the Henri Mondor hospital in 1986 according to phenotypes of beta-lactam antibiotic resistance].

Susceptibility to Augmentin (AUG) was studied as a function of resistance phenotypes toward amoxicillin (AMX), carbenicillin (CAR), cephalothin (CFT) and cefotaxime (CTX) for 1817 strains of Escherichia coli isolated at Henri-Mondor hospital during 1986. For strains susceptible to the 4 beta-lactams (phenotype SSSS: 66%), the median zone diameter observed with AUG was 26.4 mm. It was slightly inferior (22.1) for acquired - penicillinase producing strains (phenotype RRSS: 21.5%), but zone diameters were greater than or equal to 21 mm for over than 75% of these strains. Strains of phenotype RRIS (6%), probably high penicillinase-producers, were generally intermediate to AUG (median zone diameter: 17.8), showing partial inhibition of enzyme by clavulanic acid. Cephalosporinase hyperproducers mutants (phenotype RSRS: 4%) and strains with a RRRS phenotype (2.5%), probably penicillinase and cephalosporinase producers, were resistant to AUG (median zone diameters: 15.6 and 12.6 mm). Among rarely observed phenotypes, some were readily integrated to major phenotypes: RSIS, ISRS and ISIS to phenotype RSRS; RIRS to phenotype RRRS; IISS to phenotype RRSS; apparently "aberrants" phenotypes (ISSS, RSSS, SSIS, SSRS) required interpretation of results as a function of observed zone diameters and at time a verification of tests. This study confirms the in vitro activity of AUG on penicillinase producing E. coli; in addition simultaneous reading of zone diameters observed with AMX, CAR, CFT and CTX, permitted to infer the probable mechanism of resistance to beta-lactams and therefore to correct possible discrepancies observed in antibiogram results.