Comparative activity of ceftizoxime and four other cephalosporins against gram negative bacteria and their sensitivity to beta-lactamases.

The in vitro activity of ceftizoxime compared with other beta-lactamase stable compounds was assessed against recent urinary gram negative isolates. 343 bacterial strains were isolated from patients affected by UTI, identified by standard bacteriological methods and investigated for their production of beta-lactamases by Nitrocefin test. MICs and MBCs of ceftizoxime, ceftriaxone, cefamandole, cefoxitin and cefotaxime were determined by a miniaturized dilution broth method against all beta-lactamase producing bacteria (129 out of 343). Sensitivity of antibiotics to beta-lactamases isolated and semi-purified by ultrasonic disruption and high speed centrifugation was assessed by a spectrophotometric method. In vitro antibacterial activity of each antibiotics was correlated to their sensitivity to isolated beta-lactamases. Ceftizoxime showed lower MIC and MBC values and lower MBC/MIC ratio than the other compounds against all the bacteria including Pseudomonas. Ceftizoxime was not hydrolized by any isolated beta-lactamase.