Study of in vitro antibacterial activity of 19 antimicrobial agents against Pseudomonas aeruginosa

The in vitro antibacterial activity of 19 antimicrobial agents against 40 strains of P aeruginosa was studied. The 19 antimicrobial agents included 7 semisynthetic penicillins, 6 third generation cephalosporins, 5 aminoglycosides and 1 quinolone agent. The minimal inhibition concentrations (MIGs) were measured by the serial dilution on solid agar. Ceftazidime was the most active in 19 antimicrobial agents again P aeruginosa (MIC50: 1 microgram/ml, MIC90: 2 micrograms/ml) Amikacin and ofloxaxin followed it in activity. Acylureido-penicillins, such as azlocillin, furbenicillin and piperacillin were highly active against P aeruginosa, which could inhibit, 92.5%, 90% and 85% of these strains at a concentration of 8 micrograms/ml. Cefsulodine and cefoperazone were also active against the same strains, inhibiting 92.5% and 99% of the strains at a concentration of 8 micrograms/ml. The potency of the agents mentioned above against P. aeruginosa was similar to that of aminoglycosides. The drug susceptibility of 10 strains isolated in our hospital was compared with that of 29 strains of other hospitals in Beijing. The MICS of 5 penicillins and 3 cephalosporins against the isolates of our hospital was higher than that of other hospitals, suggesting that the susceptibility of beta-lactam antibiotics against isolates of our hospital was lower. The effects of combined use of azlocillin with oxacillin and piperacillin with ofloxacin against 4 strains of carbenicillin-resistant P aeruginosa was studied using check-board testing. The synergy and partial synergy were observed in both combinations.