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.
Adamsson
L
L
National Bacteriological Laboratory and Karolinska Hospital, 10521, Stockholm, Sweden.
Dornbusch
K
K
Hallander
H O
HO
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