title: Comparative activity of N-formimidoyl thienamycin with third generation cephalosporins and ureido penicillins against multiple resistant Serratia marcescens.
abstract: Twenty multiple resistant clinical isolates were tested with N-formimidoyl thienamycin, moxalactam, cefotaxime, cefoperazone, and the three ureidopenicillins: azlocillin, mezlocillin, and piperacillin. A concentration of less than 0.97 microgram/ml inhibited 100% of organisms for N-f-thienamycin and cefotaxime, 90% for moxalactam, and 60% for cefoperazone. An increase in inoculum from 10(3) to 10(6) cells reduced activity fourfold for 95% of isolates with cefoperazone, 70% with N-formimidoyl thienamycin, 65% for cefotaxime, but only 15% for moxalactam. For ureidopenicillins, 85% of strains tested had MIC's less than or equal to 15.6 micrograms/ml. An inoculum effect was observed in only 35-50%. At 10(3), the cidal concentration was the same or twofold greater than the inhibitory level for N-f-thienamycin and cephalosporins in 70% of strains tested and 65% for penicillins. With 10(6), the 70% value remained for N-f-thienamycin but was reduced to 45% for cefotaxime and 25% for moxalactam; 85% demonstrated greater than eightfold differences with cefoperazone. Single step high-level resistance was observed to moxalactam (20%). Carbenicillin resistant strains were cross-resistant to the ureidopenicillins. N-f-thienamycin and cefotaxime appeared comparable, although important differences between morphological alteration and metabolism may influence their therapeutic effectiveness.
mesh_terms: D001390:Azlocillin; D002438:Cefoperazone; D002439:Cefotaxime / Q000494:pharmacology; D002511:Cephalosporins / Q000494:pharmacology*; D002513:Cephamycins / Q000494:pharmacology; D006801:Humans; D015378:Imipenem; D007769:Lactams / Q000494:pharmacology; D008802:Mezlocillin; D008826:Microbial Sensitivity Tests; D009070:Moxalactam; D010403:Penicillin Resistance; D010406:Penicillins / Q000494:pharmacology*; D010878:Piperacillin; D012706:Serratia marcescens / Q000187:drug effects*
chemical_list: D002511:Cephalosporins; D002513:Cephamycins; D007769:Lactams; D010406:Penicillins; D015378:Imipenem; D002438:Cefoperazone; D001390:Azlocillin; D002439:Cefotaxime; D008802:Mezlocillin; D009070:Moxalactam; D010878:Piperacillin