SURVEILLANCE OF ANTIMICROBIAL RESISTANCE Multicenter Evaluation of the Antimicrobial Activity for Six Broad-Spectrum -Lactams in Venezuela Using the Etest Method The Venezuelan Antimicrobial Resistance Study Group, Michael A. Pfaller, Ronald N. Jones, and Gary V. Doern In early 1997, a 15-laboratory surveillance project was initi- ated in Venezuela to monitor the potency and spectrum of 6 broad-spectrum antimicrobial agents (cefepime, cefotaxime, ceftazidime, piperacillin, piperacillin/tazobactam, and imi- penem) tested against approximately 100 organisms per partic- ipant 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 -lactam class drugs tested, imipenem and cefepime were the most active against all isolates tested. Over- all, the rank order of susceptibility of the six agents was imi- penem (97.2% susceptible; MIC 90 2 g/mL)  cefepime (92.8%; MIC 90 6 g/mL)  piperacillin/tazobactam (77.2– 83.0%; MIC 90  256 g/mL)  cefotaxime (72.2%; MIC 90  256 g/mL)  piperacillin (56.8–65.8%; MIC 90  256 g/ mL)  ceftazidime (64.6%; MIC 90 128 g/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 -lactamases (ESBLs) and stably derepressed Bush group 1 cephalospori- nases were documented in strains of Klebsiella spp. and En- terobacters, respectively. These data should be used to guide empiric therapy with -lactams in Venezuela, and additionally will provide a reference statistical baseline to which future studies in this nation can be compared. © 1998 Elsevier Science Inc. INTRODUCTION The problem of antimicrobial resistance among Gram-negative and Gram-positive bacterial patho- gens is a global issue (Swartz 1994; Spencer et al. 1997). As such, it is important that well-controlled surveillance studies be performed in different coun- tries to assess the frequency of resistance among commonly used antimicrobial agents, as well as to evaluate the potency and spectrum of activity of new agents against the emerging resistant pathogens (Jones et al. 1994; Sader et al. 1997; Spencer et al. 1997). This is especially true in the case of -lactam agents, as the prevalence of potent -lactamases may vary considerably from one geographic area to an- other (Phelps et al. 1986; Sanders and Sanders 1988; Philippon et al. 1994; Moosdeen 1997). In conducting such studies, it is essential that the in vitro test method used be of reference quality, quantitative, rigorously standardized and controlled, and be ca- pable of assessing a wide range of antimicrobial con- From the University of Iowa College of Medicine (MAP, RNJ, GVD), Iowa City, Iowa, USA. Address reprint requests to Michael A. Pfaller, M.D., Medical Microbiology Division, Department of Pathology, C606 GH, University of Iowa College of Medicine, Iowa City, IA 52242, USA. Received 30 June 1997; accepted 12 August 1997. DIAGN MICROBIOL INFECT DIS 1998;30:45–52 © 1998 Elsevier Science Inc. All rights reserved. 0732-8893/98/$19.00 655 Avenue of the Americas, New York, NY 10010 PII S0732-8893(97)00158-2