Primary Article
β-Lactamase-Positive Strains of Haemophilus influenzae: Susceptibility to and Inactivation of β-Lactam Antibiotics
Abstract
ABSTRACT:Susceptibility and time-kill studies were done with low and high inocula of both β-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 β-lactamase-positive strains. All six antibiotics were highly active against the low inoculum (104 to 105 colony-forming units/ml) of β-lactamase-negative strains; ceftriaxone, moxalactam, and cefoperazone were equally active against the same inoculum concentration of β-lactamase-positive strains. In contrast, cefamandole, mezlocillin, and ampicillin were less active against the low inoculum of β-lactamase-positive H influenzae. A marked inoculum effect occurred with the high inoculum (107 to 108 CFU/ml) with all six antibiotics, regardless of β-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 β-lactamase-positive H influenzae.This content is limited to qualifying members.
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