title: In-vitro activity of cefaclor, cephalexin and ampicillin against 2458 clinical isolates of Haemophilus influenzae.
abstract: The zone sizes and MICs of ampicillin, cefaclor and cephalexin were determined for 2458 clinical isolates of Haemophilus influenzae collected in 1986 during a national survey of the prevalence of resistance in this species. Cefaclor showed greater in-vitro activity than cephalexin against all isolates, with a modal MIC of 4 mg/l compared with 8 mg/l. MIC50 values for the 2201 ampicillin-sensitive and 157 beta-lactamase-positive resistant strains were similar for both cephalosporins (4 mg/l for cefaclor, and 8 mg/l for cephalexin). A further 100 strains with a reduced zone (less than 20 mm) to a 2 micrograms ampicillin disc showed a definite (MIC greater than or equal to 4 mg/l) or intermediate (MIC 1 or 2 mg/l) degree of intrinsic resistance to ampicillin. Both cephalosporins showed a marked and significant rise in MIC values for this group. Cefaclor is the more active agent against ampicillin-sensitive and beta-lactamase-positive H. influenzae but strains with an intrinsic mechanism of resistance to ampicillin are markedly less sensitive to both cefaclor and cephalexin.
authors.affiliation: Department of Medical Microbiology, London Hospital Medical College, UK.
authors.forename: M
authors.initials: M
authors.lastname: Powell
authors.forename: J D
authors.initials: JD
authors.lastname: Williams
mesh_terms: D000667:Ampicillin / Q000494:pharmacology*; D000668:Ampicillin Resistance; D002433:Cefaclor / Q000494:pharmacology*; D002506:Cephalexin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D004352:Drug Resistance, Microbial; D006192:Haemophilus Infections / Q000382:microbiology; D006193:Haemophilus influenzae / Q000187:drug effects* / Q000201:enzymology; D006801:Humans; D008826:Microbial Sensitivity Tests; D001618:beta-Lactamases / Q000032:analysis
chemical_list: D002433:Cefaclor; D000667:Ampicillin; D001618:beta-Lactamases; D002506:Cephalexin