Antimicrobial therapy of postpartum endomyometritis. I. Comparative susceptibility of mezlocillin and other antibiotics to genital anaerobic bacteria.

The in vitro activity of mezlocillin, a new ureidopenicillin, against 377 obligate anaerobes from the female genital tract, was studied by an agar dilution technique. Mezlocillin demonstrated broad-spectrum activity against all genital obligate anaerobes, with a geometric mean minimum inhibitory concentration (MIC) of 4.2 microgram/ml, and inhibited 84% of B. fragilis and 99% of all isolates at 64 microgram of the antibiotic per milliliter. At readily attainable serum concentrations, mezlocillin inhibited significantly more isolates than cefoxitin (p less than 0.0005), ampicillin (p less than 0.0005), penicillin G (p less than 0.005), and clindamycin (p less than 0.025); its activity was comparable to that of carbenicillin and chloramphenicol. Mezlocillin was significantly more active than ampicillin (p less than 0.025), penicillin G (p less than 0.025), and clindamycin (p less than 0.05) against Bacteroides species other than B. fragilis and B. melaninogenicus.