ROUTINE DETECTION OF INHIBITORS RESISTANT TEM BETA-LACTAMASES (IRT) AND OXACILLINASES (OXA) IN ESCHERICHIA-COLI

SUMM. Comparative study of twenty two strains of Escherichia coli prod ucing a well-characterized penicillinase of the OXA type (oxacillinase ) or of the IRT type (TEM resistant to inhibitors) evidenced different criteria leading to the distinction of two groups of strains, accordi ng to the type of the harboured enzyme. Applied to eleven clinical str ains, these criteria were always concordant with the determination of the isoelectric point, of hybridation and of oligotyping using probes for the classification into OXA or IRT type. We therefore propose the measurement of three inhibition diameters on antibiogram (cefepime, me cillinam and ceftazidime) for the routine distinction of the two enzym es. The interest of the easy characterization of these enzymes is rein forced by our findings that, as for all OXA strains, the inoculum effe ct which is displayed by some third-generation cephalosporins is very important and should be taken into account in the treatment of severe infections.