The Optimum Agent for Screening and Confirmatory Tests for Extended-Spectrum Beta-Lactamases in Escherichia coli and Klebsiella pneumoniae in Ramathibodi Hospital, Thailand

The purpose of this study was to determine the appropriate antibiotic for extended-spectrum beta-lactamases (ESBLs) screening and confirmatory tests in Escherichia coli and Klebsiella pneumoniae. The sensitivity of each antibiotic recommended by the National Committee for Clinical Laboratory Standards (NCCLS) to screen for ESBL production was compared. A total of 271 E. coli and 185 K. pneumoniae isolated in clinical microbiology laboratory, Ramathibodi Hospital, Thailand were tested for ESBL by screening and confirmatory disc diffusion methods recommended by the NCCLS. There were 182 isolates that were positive for ESBL confirmatory test. The sensitivity of the screening methods of aztreonam, cefpodoxime, ceftriaxone, cefotaxime, and ceftazidime were 96.70, 97.25, 97.25, 97.25, and 74.18 percent, respectively. Almost all isolates (45/47) that were false negative for ESBL screening by ceftazidime still effectively hydrolyzed the other agents, and were thus presumed to be CTX-M-type-ESBL-producing strains. We conclude that ceftazidime alone is not sensitive enough to be used for screening and confirmation for ESBL production in our hospital. A genotypic method to determine the presence of CTX-M-type ESBL is thus needed. (J Infect Dis Antimicrob Agents 2004;21:1-5.) INTRODUCTION Extended-spectrum beta-lactamases (ESBLs) produced by gram-negative bacilli are major causes of the bacterial resistance to penicillins and cephalosporins. Screening and confirmatory testing for ESBL production are important in assisting clinicians to select the appropriate antibiotics to treat infections.1-3 The disc diffusion method is widely used in most clinical microbiology laboratory because of its low cost and convenience to perform, The National Committee for Clinical Laboratory Standards (NCCLS) recommends the standard methods for screening and confirmation for ESBL.1,4 In screening test, bacterial isolates were tested with at least one of five antibiotic Clinical Microbiology Laboratory, Department of Pathology, Faculty of Medicine Ramathibodi Hospital, Mahidol University, Bangkok