title: Beta-lactamase-positive strains of Haemophilus influenzae: susceptibility to and inactivation of beta-lactam antibiotics.
abstract: Susceptibility and time-kill studies were done with low and high inocula of both beta-lactamase-positive and -negative strains of Haemophilus influenzae with cefamandole, ampicillin, cefoperazone, mezlocillin, moxalactam, and ceftriaxone. Bioassay was done to test for antibiotic inactivation by beta-lactamase-positive strains. All six antibiotics were highly active against the low inoculum (10(4) to 10(5) colony-forming units/ml) of beta-lactamase-negative strains; ceftriaxone, moxalactam, and cefoperazone were equally active against the same inoculum concentration of beta-lactamase-positive strains. In contrast, cefamandole, mezlocillin, and ampicillin were less active against the low inoculum of beta-lactamase-positive H influenzae. A marked inoculum effect occurred with the high inoculum (10(7) to 10(8) CFU/ml) with all six antibiotics, regardless of beta-lactamase production. In time-kill studies, marked differences in bacterial killing resulted after low and high inocula. Ampicillin, cefamandole, cefoperazone, and mezlocillin were rapidly inactivated by the high inoculum of beta-lactamase-positive H influenzae.
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002435:Cefamandole / Q000494:pharmacology; D002438:Cefoperazone / Q000494:pharmacology; D002439:Cefotaxime / Q000031:analogs & derivatives / Q000494:pharmacology; D002443:Ceftriaxone; D006193:Haemophilus influenzae / Q000187:drug effects* / Q000201:enzymology; D008802:Mezlocillin / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D009070:Moxalactam / Q000494:pharmacology; D001618:beta-Lactamases / Q000096:biosynthesis
chemical_list: D000900:Anti-Bacterial Agents; D002435:Cefamandole; D002443:Ceftriaxone; D000667:Ampicillin; D002438:Cefoperazone; D001618:beta-Lactamases; D002439:Cefotaxime; D008802:Mezlocillin; D009070:Moxalactam