Influence of bacterial beta-lactamase production on susceptibility in agar or broth to new cephalosporins.
Of 39 cephalothin-resistant (MIC > or =16 mg/l) strains of Enterobacteriaceae, 50% were inhibited by cefamandole 4 mg/l, cefoperazone 1 mg/l, cefuroxime 16 mg/l, cefoxitin 8 mg/l, ceftazidime 0.5 mg/l and moxalactam 0.1 mg/l in Mueller-Hinton agar with inocula of 106 bacteria/ml. The MICs in broth with the respective antibiotics were eight-, four-, two-, sixteen- and eightfold higher. Of 22 Pseudomonas aeruginosa strains, 50% were inhibited in agar by ceftazidime 1 mg/l and moxalactam 16 mg/l and in broth by 4 and 64 mg/l, respectively. Cefamandole was the most susceptible and ceftazidime and moxalactam the most stable to inactivation by crude beta-lactamase preparations from the strains. A higher broth/agar MIC ratio correlated, with some exceptions, to the production of active enzymes. Growth curves in the presence of antibiotic with or without beta-lactamase inhibitor confirmed that the elevated broth MICs were attributable to beta-lactamase production. High broth/agar MIC ratios were also found with strains that gave inactive preparations particularly against ceftazidime and moxalactam, which must be due to other factors.
National Bacteriological Laboratory and Karolinska Hospital, 10521, Stockholm, Sweden.
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L
Adamsson
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Dornbusch
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HO
Hallander
D000362:Agar; D000900:Anti-Bacterial Agents / Q000378:metabolism* / Q000494:pharmacology*; D002442:Ceftazidime / Q000378:metabolism / Q000494:pharmacology; D002511:Cephalosporins / Q000378:metabolism* / Q000494:pharmacology*; D019818:Clavulanic Acid / Q000494:pharmacology; D003470:Culture Media; D024881:Drug Resistance, Bacterial; D004755:Enterobacteriaceae / Q000187:drug effects; D006090:Gram-Negative Bacteria / Q000187:drug effects* / Q000201:enzymology*; D008826:Microbial Sensitivity Tests; D011550:Pseudomonas aeruginosa / Q000187:drug effects; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000096:biosynthesis*
D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D003470:Culture Media; D065093:beta-Lactamase Inhibitors; D019818:Clavulanic Acid; D000362:Agar; D002442:Ceftazidime; D001618:beta-Lactamases