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After being confronted with the isolation in our laboratory of numerous antibiotic-multiresistant Enterobacter aerogenes strains, we studied the in vitro antimicrobial activity of cefotaxime, ceftazidime, and cefepime alone or in association with sulbactam. For that, we selected 67 isolates according to their low level of susceptibility to cefotaxime. First, we deduced from a synergy test in presence of clavulanic acid and cloxacillin the production of an extended spectrum beta-lactamase (ESBL) and/or an overproduction of a chromosomal cephalosporinase. Three groups of strains were thus defined: one group of ESBL strains, another group of overproducing strains of chromosomal cephalosporinase, and a last group that produced the two types of enzymes. Minimal inhibitory concentrations (MICs) of each cephalosporin alone or in presence of 8 mg/L of sulbactam, gentamicin or amikacin were measured. Our results demonstrated the best activity of cefepime: MICs were low with a value inferior to 4 mg/L independently of the type of beta-lactamase. They were lower than 0.5 mg/L in presence of sulbactam against ESBL-producing strains. The cephalosporins could be used in association with aminoglycosides according to their susceptibility. |
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