title: Activity of semisynthetic penicillins and synergism with mecillinam against Bacteroides species.
abstract: The minimal inhibitory concentrations (MIC) of six penicillins (ampicillin, carbenicillin, ticarcillin, piperacillin, mezlocillin, and Bay k 4999) against 29 clinical isolates of Bacteriodes spp. (including Bacteroides fragilis, Bacteroides thetaiotaomicron, and Bacteroides vulgatus) were determined by an agar dilution method. Bay k 4999 was most active, followed in descending order by ampicillin, piperacillin, mezlocillin, ticarcillin, and carbenicillin. Mecillinam, a 6 beta-amidino-penicillanic acid, inhibited no strains at 50 micrograms/ml, but when compared with ampicillin, a fourfold or greater increase in MIC for ampicillin (antagonism) was noted in 3 of 29 strains, with no effect on MIC for 26 strains, whereas when combined with carbenicillin, a fourfold or greater decrease in MIC for both antibiotics (synergism) was noted in 12 strains, 4 of which had an MIC of greater than or equal to 250 micrograms/ml for carbenicillin alone. These studies demonstrate the increased activity of some newer semisynthetic penicillins and the potential synergy obtained with mecillinam and carbenicillin against Bacteroides sp.
mesh_terms: D000560:Amdinocillin / Q000494:pharmacology*; D001439:Bacteroides / Q000187:drug effects*; D004357:Drug Synergism; D008826:Microbial Sensitivity Tests; D010397:Penicillanic Acid / Q000494:pharmacology*; D010406:Penicillins / Q000494:pharmacology*
chemical_list: D010406:Penicillins; D010397:Penicillanic Acid; D000560:Amdinocillin