Comparative study on in vitro antibacterial activity of 19 antimicrobial agents against Pseudomonas aeruginosa

An in vitro antibacteri.al activity of 19 antimicrobial agents against 40 strains of P aeruginosa was studied. The 19 antimicrobial agents included: 7 semisynthetic peniciilins, 6 third generation cephalosporins, 5 aminoglycosides and 1 quinoline agent. The MICs were measured by a serial dilution on solid agar.Ceftazidime was found to be the most active among the 10 antimicrobial agents against P aeruginosa (MIC₅₀ 1μg/ml, MIC₉₀ 2μg/ml).The drug susceptibility of 10 strains isolated in our hospital was compared with 29 strains in other hospital in Beijing. The MIC of 5 penicillins and 3 cephalosporins against the isolates from our hospital was higher than that of microorganisms from other hospital. It was also found that susceptibility of β-lactam antibiotics against isolates from our hospital became lower.The effect of combination azlocillin with oxacillin and that of piperacillin with ofloxacin against 4 carbenicillin-resistant P aeruginosa was studied, using checked-board testing. Synergy and partial synergy were observed in both combinations.