The AcrAB RND efflux system from the live vaccine strain of Francisella tularensis is a multiple drug efflux system that is required for virulence in mice

The ability of bacterial pathogens to infect and cause disease is dependent upon their ability to resist antimicrobial components produced by their host, such as bile acids, fatty acids and other detergent-like molecules, and products of the innate immune system (e.g. cationic antimicrobial peptides). Bacterial resistance to the antimicrobial effects of such compounds is often mediated by active efflux systems belonging to the resistance-nodulation-division (RND) family of transporters. RND efflux systems have been implicated in antibiotic resistance and virulence extending their clinical relevance. In this report the hypothesis that the Francisella tularensis AcrAB RND efflux system contributes to antimicrobial resistance and pathogenesis has been tested. A null mutation was generated in the gene encoding the AcrB RND efflux pump protein of the live vaccine strain of F. tularensis. The resulting mutant exhibited increased sensitivity to multiple antibiotics and antimicrobial compounds. Murine challenge experiments revealed that the acrB mutant was attenuated. Collectively these results suggest that the F. tularensis AcrAB RND efflux system encodes a multiple drug efflux system that is important for virulence.