Comparative activity of eight antimicrobial agents against clinical bacterial isolates from the united states, measured by two methods

In a surveillance study conducted during 1992–1993 at 83 medical institutions of different types and sizes (e.g., laboratories, community hospitals, teaching hospitals) and from different geographical areas of the United States, clinical bacterial isolates were tested for their susceptibility to eight comparative antimicrobial agents (cefepime, ceftazidime, cefotaxime, ceftriaxone, ciprofloxacin, gentamicin, imipenem, and piperacillin). A total of 12,574 isolates were tested by either the Etest method (AB Biodisk) or a microdilution method (MicroScan) in the participating laboratories; 11.8% of these isolates were subsequently retested for quality assurance purposes by both methods in a central laboratory. The results obtained in the central laboratory were essentially the same as the results obtained in the participating laboratories. This article presents data for gram-negative and grampositive isolates other than Streptococcus pneumoniae, the results of which have been previously published. Antimicrobial susceptibility results obtained with the two different minimum inhibitory concentration (MIC) methods—MicroScan and Etest—showed that most isolates of Enterobacteriaceae were susceptible to cefepime, exceeding the activity of ceftazidime, ceftriaxone, and cefotaxime, principally because of the greater activity of cefepime against the species that produce Bush group 1 β-lactamases (predominantly Enterobacter cloacae, Enterobacter aerogenes, and Citrobacter freundii). In addition, the activity of cefepime against Pseudomonas aeruginosa isolates was essentially equivalent to that of ceftazidime and greater than that of third-generation cephalosporins. Most methicillin-susceptible Staphylococcus aureus were susceptible to all the cephalosporins, whereas methicillin-resistant S. aureus and enterococci were resistant. Overall, the most active antimicrobials in this study were imipenem, ciprofloxacin, and cefepime, but the activity of all the antimicrobials varied with different species. Categorically, the results from the microdilution and Etest methods were equivalent.