Effectiveness of colistin with rifampicin and meropenem against colistin-resistant Acinetobacter baumannii strains: an in vitro study

Introduction: Antibiotic resistance is an important issue that may worsen the clinical evolution of high risks patients. The increasing use of colistin for the treatment of carbapenem-resistant Acinetobacter baumannii infections has led to the emergence of colistin resistance. Since A. baumannii is an important nosocomial pathogen and is responsible for severe infections, the use of antimicrobial combinations has been strongly recommended. Materials & Methods: The aim of this study is to evaluate the in vitro effect of colistin/rifampicin and colistin/meropenem combinations against colistin-resistant A. baumannii isolates using two rapid E-test methods. Results: Synergy was observed with colistin in combination with rifampicin against all the isolates. Otherwise, colistin/meropenem combination showed indifference by E-test cross formation and synergy dependent by meropenem concentration by E-test gradient. Discussion and conclusion: Nowadays A. baumannii is one of the most important emerging, opportunistic pathogens that can affect critical patients. Colistin, the main antibiotic effective against such bacterium, when associated with rifampicin shows an enhanced activity.