Objective: To investigate the in vitro activity of
meropenem and four other β lactams. Methods: The minimum inhibitory
concentration(MIC) of meropenem, imipenem, ceftazidime, cefepime, and
cefoperazone /
sulbactam on 554 clinical isolates were determined by E test method. The extended spectrum β lactamase (ESBLs) producing strains in Escherichia coli and Klebsiella pneumoniae were detected by ESBLs phenotype screen and confimatory method recommended by the National Committee for Clinical Laboratory Standards. Results: Eleven percent of Escherichia coli and 29% of Klebsiella pneumoniae produced ESBLs. The MICs of cefepime, cefoperazone sulbactam, and ceftazidime on ESBLs producing strains were significantly higher than those on nonESBLs producing strains;there was no significant difference between the anti bacterial activity of meropenem and imipenem against ESBLs producing and ESBLs non producing strains. Against Enterobacter spp, meropenem was the most active agent(95% susceptible),followed by imipenem (82%), cefepime (71%), ceftazidime, and cefoperazone sulbactam (57%-59%).The MIC of meropenem againct Pseudomonas aeruginosa was one eighth that of imipenem; the distribution of MIC of the two drugs was similar for Acinetobacter spp. and Enterococcus spp.. Meropenem had excellent activity against Haemophilus influenzae, Streptococcus pneumoniae, and oxacillin susceptible Staphylococci. Conclusions: The order of activity of the five agents was: meropenem(94.6% susceptible)>imipenem (90.1%)>cefepime (77.6%), cefoperazone /sulbactam (77.5%) and ceftazidime (77.6%).