In Vitro Antimicrobial Activities of Meropenem, Ciprofloxacin, Colistin Alone and in Combinations Against Meropenem-Resistant Pseudomonas Aeruginosa

Determinations of in vitro antimicrobial activities of meropenem, ciprofloxacin, colistin alone and in combinations against 20 clinical isolates of P. aeruginosa have shown that 16 isolates (80%) were multidrug-resistant (MDR) isolates. All isolates were resistant to meropenem (MIC90=32 μg/mL) whereas 4 out of 20 isolates (20%) were susceptible to ciprofloxacin (MIC90=64 μg/mL). Furthermore, all isolates were susceptible to colistin (MIC90=2 μg/mL). With checkerboard method, it has been shown that meropenem in combination with ciprofloxacin or colistin and ciprofloxacin in combination with colistin had synergistic effects with drug concentration within the therapeutic serum level against 3, 6 and 4 isolates, respectively. For triple combination of meropenem, ciprofloxacin and colistin, the synergistic effect was observed in 5 isolates. Taken these results into account, meropenem in combination with colistin may be optimal alternative treatment for meropenem-resistant P. aeruginosa infections.