Susceptibility of 100 blood isolates of Pseudomonas aeruginosa to 19 antipseudomonal antibiotics: old and new.

The in vitro susceptibility of 19 antipseudomonal antibiotics, old and new, were tested against 100 blood isolates of Pseudomonas aeruginosa. The isolates were taken from consecutive bacteremic patients hospitalized in nine Pittsburgh hospitals from 1983 to 1984. Twelve percent of isolates tested were tobramycin-resistant. All of the tobramycin-resistant isolates were sensitive to apalcillin, azlocillin, aztreonam, cefsulodin, ceftazidime, ciprofloxicin, and imipenem. Two isolates were resistant in vitro to all beta-lactam antibiotics tested, but sensitive to all aminoglycosides. One hundred percent of isolates tested were susceptible to imipenem, whereas, 98% were susceptible to apalcillin and cefsulodin. The lowest MIC90 was 2 mg/L for ciprofloxicin. Tolerance of P. aeruginosa (MIC90/MBC90 ratio greater than 32) was not observed for any antimicrobial agent.