SURVEY OF ANTIMICROBIAL ACTIVITY OF 4 COMMONLY USED 3RD-GENERATION CEPHALOSPORINS TESTED AGAINST RECENT BACTERIAL ISOLATES FROM 10 AMERICANMEDICAL-CENTERS, AND ASSESSMENT OF DISK DIFFUSION TEST-PERFORMANCE

Over 2,000 clinical isolates from ten American medical centers were te sted for susceptibility to cefotaxine, ceftriaxone, ceftizoxime, and c eftazidime by both broth microdilution and disk diffusion methods. Typ ically resistant (e.g. enterococci) and highly susceptible (e.g. strep tococci) isolates showed no change in susceptibility patterns compared to previous surveys. Pseudomonas aeruginosa and Stenotrophomonas malt ophilia exhibited significant decreases in susceptibility to these cep halosporins. Among Escherichia coli and Klebsiella spp isolates, two t o three percent were resistant to one of the four drugs whereas they w ere very susceptible to the other three. Of the four antibiotics, the cefotaxime disk diffusion test results correlated best with the microd ilution results. With the other three drugs the disk diffusion test yi elded 1 to 9% more susceptible test results and 1 to 20% fewer resista nt test results than broth microdilution when testing gram negative ba cilli. The clinical significance of such discrepancies is not known, b ut the impact on antibiotic susceptibility surveys and antibiogram com parisons could be significant.