The comparative in vitro susceptibility of cefazolin-resistant organisms to six cephalosporins, four penicillins, and three aminoglycosides.

One thousand thirty-seven cefazolin-resistant, gram-negative clinical isolates including members of the family Enterobacteriaceae, pseudomonads, and other nonfermenters were tested against a variety of newer antimicrobial agents by microdilution. Most of the Enterobacteriaceae were resistant to the second-generation cephalosporins, but highly susceptible to the third-generation agents and the broad-spectrum penicillins, 90% of the strains being inhibited at attainable serum concentrations. Cefoperazone and the penicillins had good activity against the Pseudomonas species, but the aminoglycosides remained the most active agents against all the gram-negative bacilli tested except Pseudomonas maltophilia.