Comparative antibacterial activity of cefotaxime, ceftazidime and cefepimewith regard to different strain of Enterobacter aerogenes selected for their resistance to third-generation cephalosporins.

After being confronted with the isolation in our laboratory of numerous ant ibiotic-multiresistant Enterobacter aerogenes strains, we studied the in vi tro antimicrobial activity of cefotaxime, ceftazidime, and cefepime alone o r in association with sulbactam. For that, we selected 67 isolates accordin g to their low level of susceptibility to cefotaxime. First, we deduced fro m a synergy test in presence of clavulanic acid and cloxacillin the product ion of an extended spectrum beta -lactamase (ESBL) and/or an overproduction of a chromosomal cephalosporinase. Three groups of strains were thus defin ed : one group of ESBL strains, another group of overproducing strains of c hromosomal cephalosporinase, and a last group that produced the two types o f enzymes. Minimal inhibitory concentrations (MICs) of each cephalosporin a lone or in presence of 8 mg/L of sulbactam, gentamicin or amikacin were mea sured. Our results demonstrated the best activity of cefepime : MICs were l ow with a value inferior to 4 mg/L independantly of the type of beta -lacta mase. They were lower than 0.5 mg/L in presence of sulbactam against ESBL-p roducing strains. The cephalosporins could be used in association with amin oglycosides according to their susceptibility. (C) 2000 Editions scientifiq ues et medicales Elsevier SAS.