Agar (disk) diffusion test susceptibility of clinical isolates of Pseudomonas aeruginosa to azlocillin, cefotaxime, cefsulodin, lamoxactam, mezlocillin, and piperacillin.

The standardized Bauer-Kirby agar diffusion test served to examine 100 clinical isolates of Pseudomonas aeruginosa against various recently introduced broad-spectrum penicillins and cephalosporins. Neither cefotaxime nor lamoxactam displayed significant activity against this microorganism. Azlocillin, cefsulodin, and piperacillin were significantly more effective (p less than 0.0001) than mezlocillin against the majority of isolates. When compared individually, azlocillin and piperacillin displayed comparable in vitro activity; the same was true for cefsulodin compared with piperacillin. On the other hand, cefsulodin was somewhat more active than azlocillin (p less than 0.05, greater than 0.01) against P. aeruginosa. These data should enable diagnostic laboratories to curtail the number of antimicrobial drugs routinely utilized to examine clinical isolates of P. aeruginosa for antibiotic susceptibility, i.e., piperacillin exclusively.