Evaluation of Synergistic Effect of Colistin with Levofloxacin and Meropenem against Multidrug-resistant Acinetobacter baumannii

Many antibiotics currently in use show limited effectiveness against Acinetobacter baumannii due to its high resistance. The current investigation set out to assess the synergistic effect of colistin in combination with levofloxacin and meropenem to provide an appropriate antibiotic regimen for infections caused by multidrug-resistant A. baumannii (MDR-AB).

Utilizing the broth microdilution approach, the minimum inhibitory concentration (MIC) of levofloxacin, colistin, and meropenem versus isolates of MDR-AB obtained from hospitalized individuals with nosocomial infections caused by this pathogen was ascertained. The checkerboard approach was also used to determine the antibiotics' simultaneous effects on the pathogen.

Twenty isolates underwent testing. Every isolate was meropenem-resistant. Conversely, all 20 isolates showed sensitivity to colistin, with a MIC range of 0.031-2 µg/mL. The synergy test revealed that no instances of antagonistic interactions existed between meropenem and colistin in 60% of isolates, indicating partial synergy (additive impact). However, only 40% of isolates demonstrated partial synergism with no instances of antagonistic behavior when colistin and levofloxacin were administered together.

Levofloxacin and meropenem exhibit respectable synergistic effects when combined with colistin; as a result, these combinations may be clinically assessed for MDR-AB infections.