title: Effect of beta-lactamase expression on susceptibility of local isolates of Enterobacter cloacae, Serratia marcescens and Pseudomonas aeruginosa to beta-lactam antibiotics.
abstract: During surveillance studies, a total of 66 strains of gram-negative bacilli (28 Enterobacter cloacae, 20 Serratia marcescens and 18 Pseudomonas aeruginosa) with a reduced susceptibility to third-generation cephalosporins, aztreonam and amikacin were isolated from documented infections. All isolates were highly susceptible to imipenem and sparfloxacin. beta-Lactamase activity was demonstrated in all isolates of E. cloacae and S. marcescens, and in 77% of P. aeruginosa isolates. Inducible beta-lactamase activity was detected in 80, 65 and 40% of E. cloacae, S. marcescens and P. aeruginosa isolates, respectively, when cefoxitin was used as an inducer. More inducible beta-lactamase producers were observed when imipenem was used as an inducer. Isolates of E. cloacae, and to a lesser extent S. marcescens, expressed a wide spectrum of beta-lactamase activities. There was a good correlation between baseline beta-lactamase activity and the respective MIC of ceftazidime, cefotaxime and ceftriaxone, and to a lesser extent aztreonam in E. cloacae and S. marcescens isolates. Only one isolate of E. cloacae demonstrated an extended beta-lactamase activity. The data suggest that the resistance of E. cloacae and S. marcescens isolates to beta-lactam antibiotics is largely dependent upon hyperproduction of beta-lactamase.
authors.affiliation: Division of Microbiology, College of Pharmacy, King Saud University, Riyadh, Saudi Arabia.
authors.forename: M A
authors.initials: MA
authors.lastname: Ramadan
authors.forename: A F
authors.initials: AF
authors.lastname: Tawfik
authors.forename: A M
authors.initials: AM
authors.lastname: Shibl
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D018432:Drug Resistance, Multiple; D004754:Enterobacter / Q000187:drug effects / Q000201:enzymology*; D006801:Humans; D015378:Imipenem / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000201:enzymology*; D012706:Serratia marcescens / Q000187:drug effects / Q000201:enzymology*; D013045:Species Specificity; D001618:beta-Lactamases / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D015378:Imipenem; D001618:beta-Lactamases