In-vitro activities of various antibiotics, alone and in combination with amikacin against Pseudomonas aeruginosa.

The in-vitro activities of various antibiotics, either alone or in combination with amikacin were assessed using clinical isolates of Pseudomonas aeruginosa. The minimum inhibitory concentrations (MIC) of these antibiotics were determined by microbroth dilution method against 50 clinical strains. The MIC values showed that 96, 94, and 74% of the isolates were susceptible or moderately susceptible to amikacin, meropenem and ceftazidime, respectively. The in vitro activities of ceftazidime and meropenem in combination with amikacin were determined by microbroth chequerboard technique and results were interpreted using the fractional inhibitory concentration (FIC) index. With a FIC index of < or =0.5 as borderline, synergistic interactions were more frequent with ceftazidime (70.8%) than with meropenem (40%). No antagonism was observed.