Comparison of two techniques for measurement of in vitro killing kinetics of five antibiotics against Pseudomonas aeruginosa.

The in vitro activity of ticarcillin, imipenem, gentamicin, amikacin and ciprofloxacin against six Pseudomonas aeruginosa isolates was evaluated by two time-killing curve methods: the conventional broth technique, and another method previously described which employs a transfer filter membrane. The patterns of the killing curves obtained over a 5 h period with the two techniques were similar. In contrast to the results obtained for beta-lactam agents, the reduction of inoculum was great and increased with the concentration for aminoglycosides and ciprofloxacin. After 5 h, regrowth of the six strains tested was observed in broth with all antibiotics, whereas a bactericidal effect was observed over 24 h with the filter membrane method. Further studies are warranted to determine the reasons for this difference.