In vitro susceptibility of Pseudomonas aeruginosa from bacteremic and fibrocystic patients to four quinolones and five other antipseudomonal antibiotics.

The in vitro antibacterial activities of 4 quinolones, 4 antipseudomonal beta-lactam antibiotics and tobramycin were determined by an agar dilution technique against 206 clinical isolates of Pseudomonas aeruginosa. 176 isolates derived from blood cultures (BC), the remaining 30 were piperacillin-resistant strains from sputum of cystic fibrosis (CF) patients. The CF strains were more resistant to all drugs tested and differed greatly in susceptibility pattern from the BC strains. Ciprofloxacin, ofloxacin and tobramycin were the most active drugs against the CF strains. More than 80% of the BC strains were susceptible to piperacillin and cefsulodin and more than 90% to ceftazidime, tobramycin, ciprofloxacin and ofloxacin. On a weight basis ciprofloxacin was the most active drug in both groups of strains. Our in vitro data suggest that several valuable drugs are now available in the treatment of infections caused by P. aeruginosa strains not previously exposed to antipseudomonal agents.