Prevalence of eight resistance-nodulation-division efflux pump genes in epidemiologically characterized Acinetobacter baumannii of worldwide origin

The increasing emergence of multidrug-resistant Acinetobacter baumannii constitutes a worldwide threat in hospital settings. Efflux-mediated resistance, particularly the resistance-nodulation-division (RND)-type efflux pumps, contributes significantly to decreased susceptibility to multiple antibiotics when overexpressed. Using PCR-based detection, the prevalence of genes encoding the RND efflux pumps AdeB, AdeJ and AdeG was investigated amongst 144 epidemiologically characterized and geographically diverse A. baumannii isolates of worldwide origin, representing International Clones 1-8 and genotypically unique isolates. Furthermore, five putative RND-type efflux genes identified via an in silico approach were included. Five of the eight investigated efflux pump genes were present in all isolates, including adeJ and adeG; the prevalence of the others varied between 65 and 97%. No association between the presence of one or multiple pumps to a specific clonal lineage was detected. The high prevalence of the efflux pump genes supports a fixed function of each individual pump that is not yet fully understood.