Contribution of efflux systems to the detergent resistance, cytotoxicity, and biofilm formation of Vibrio vulnificus

Vibrio vulnificus causes primary septicemia in immunocompromised patients following consumption of contaminated seafood. In order to cause infection, pathogenic bacteria require mechanisms to defend against the action of host-derived antimicrobials, and may accomplish this task through the expression of efflux pumps. Herein, we investigated the influence of bile salts on the antimicrobial resistance mechanisms in V. vulnificus, and the contribution of efflux pumps to the bacterium's detergent resistance and virulence characteristics. Bacterial cells treated with either bile salts or Triton X-100 developed enhanced detergent resistance relative to the untreated control, and also showed increased expression of genes encoding resistance-nodulation-division (RND) efflux pumps. Further investigation on V. vulnificus mutants deficient in RND efflux pump VexB revealed them to be more susceptible to nonionic detergents. In addition, an RND efflux pump triple mutant, ΔvexBHZ, exhibited increased cytotoxicity and enhanced biofilm formation. In summary, our data indicate that V. vulnificus RND efflux pump VexB plays a key role in the resistance to nonionic detergents. Furthermore, the expression levels of efflux pumps affect the antimicrobial resistance and are involved in modulating the biofilm formation and cytotoxicity of this pathogen.