B-270. Regulatory Network of Multidrug Transporters Reveals their Physiological Role in Salmonella Virulence

K. Nishino1,2, A. Yamaguchi1;
1Osaka Univ., Osaka, JAPAN, 2PRESTO, Japan Sci. and Technology Agency, Tokyo, JAPAN.

Background: Multidrug transporters play a major role in the multidrug resistance by extruding antibiotics or biocides out of the cell. Recent discoveries support the notion that at least some multidrug transporters have specific physiological substrates because these transporters have been shown to have roles in bacterial virulence (Nishino et al. Mol. Microbiol. 61: 645-654, 2006). However, the precise roles of multidrug transporters in virulence are not clearly understood. Here we show that, in addition to their role in multidrug resistance, AcrD and MdtABC multidrug transporters in Salmonella enterica export enterobactin, a catecholate siderophore, to acquire iron from environments. Methods: We generated libraries of random gene knockouts of Salmonella enterica serovar Typhimurium by EZ-Tn KAN-2 Transposome Kit (Epicentre Biotechnologies) to identify repressors of multidrug transporters. Enterobactin efflux activities of Salmonella cells were measured by high-performance liquid chromatography (HPLC). Results: We identified that the Fur (Ferric uptake regulator) protein represses the expression of acrD and mdtABC. Fur bound to the upstream regions of acrD and mdtABC and these genes were induced under iron-limiting condition in Fur-dependent manner. Under iron-limiting condition, Salmonella secretes enterobactin to acquire iron from environments. We found that AcrD and MdtABC secrete enterobactin and these transporters were required for cell growth under iron-limiting condition. Iron is essential for Salmonella virulence. We found that the strain lacking acrD and mdtABC was attenuated for virulence in mice. Conclusion: These results reveal a previously uncharacterized physiological role for AcrD and MdtABC in iron homeostasis and virulence. Multidrug transporters could contribute both to bacterial multidrug resistance and virulence, so that they might be a good target for new drugs that can inhibit bacterial multidrug resistance and virulence.