An in-vitro comparison of new cephalosporins with special reference to Pseudomonas aeruginosa

MICs of cefoperazone, cefotaxime, ceftazidime and moxalactam were determined for staphylococci, Enterobacteriaceae, Haemophilus influenza and Neisseria gonorrhoeae. The new compounds are 10 to 100 times more active in vitro against Enterobacteriaceae and H. influenzae (including penicillinase-producing strains) than the older cephalosporins. Against N. gonorrhoeae, including penicillinase-producing strains, cefotaxime appeared to be the most active compound (MIC as low as 0.002 mg/l), while the other new cephalosporins were approximately as active as cefuroxime. Cefoperazone, cefotaxime, cefsulodin, ceftazidime, ceftriaxone and moxalactam were tested against carbenicillin susceptible (Cbs) and carbenicillin resistant (Cb(R)) strains of Pseudomonas aeruginosa. Against Cb(S) strains the lowest MIC values were obtained with ceftazidime (1 mg/l) followed by cefsulodin (1-2 mg/l), cefoperazone (2-4 mg/l), ceftriaxone (4 mg/l), moxalactam (4-8 mg/l) and cefotaxime (8-16 mg/l). Usually the susceptibility to cephalosporins of Cb(R) strains was found decreased for all compounds, but the least for ceftazidime. Considerable cross resistance with carbenicillin was noted for cefsulodin and cefoperazone only. Lysates of 19 CbR strains have been screened for the presence of constitutive beta-lactamases. Three enzyme types were found: pI 5.4 (n=8) pl 5.3 (n=5) and pI 5.7 (n=6).