Multicenter Evaluation of the Antimicrobial Activity for Six Broad-Spectrum β-Lactams in Venezuela Using the Etest Method

Abstract

In early 1997, a 15-laboratory surveillance project was initiated in Venezuela to monitor the potency and spectrum of 6 broad-spectrum antimicrobial agents (cefepime, cefotaxime, ceftazidime, piperacillin, piperacillin/tazobactam, and imipenem) tested against approximately 100 organisms per participant center (1297 strains). Ten groups of organisms were tested by the Etest method (AB BIODISK, Solna, Sweden) with results validated by concurrent quality control strain analysis. Results from all centers were tabulated and 96.3% of quality assurance tests were within ranges recommended by the National Committee for Clinical Laboratory Standards. Among the six β-lactam class drugs tested, imipenem and cefepime were the most active against all isolates tested. Overall, the rank order of susceptibility of the six agents was imipenem (97.2% susceptible; MIC 90 2 μg/mL) > cefepime (92.8%; MIC 90 6 μg/mL) > piperacillin/tazobactam (77.2–83.0%; MIC 90 > 256 μg/mL) > cefotaxime (72.2%; MIC 90 > 256 μg/mL) > piperacillin (56.8–65.8%; MIC 90 > 256 μg/mL) > ceftazidime (64.6%; MIC 90 128 μg/mL). Both cefepime and imipenem were active against ceftazidime-resistant strains of Enterobactericaeae as well as against Pseudomonas aeruginosa and oxacillin-susceptible staphylococci. Resistance phenotypes consistent with extended spectrum β-lactamases (ESBLs) and stably derepressed Bush group 1 cephalosporinases were documented in strains of Klebsiella spp. and Enterobacters, respectively. These data should be used to guide empiric therapy with β-lactams in Venezuela, and additionally will provide a reference statistical baseline to which future studies in this nation can be compared.