Temperature-regulated efflux pump/potassium antiporter system mediates resistance to cationic antimicrobial peptides in Yersinia

Most bacterial pathogens are resistant to cationic antimicrobial peptides ( CAMPs) that are key components of the innate immunity of both vertebrates a nd invertebrates. In Gram-negative bacteria, the known CAMPs resistance mec hanisms involve outer membrane (OM) modifications and specifically those in the lipopolysaccharide (LPS) molecule. Here we report, the characterizatio n of a novel CAMPs resistance mechanism present in Yersinia that is depende nt on an efflux pump/potassium antiporter system formed by the RosA and Ros B proteins. The RosA/RosB system is activated by a temperature shift to 37 degrees C, but is also induced by the presence of the CAMPs, such as polymy xin B. This is the first report of a CAMPs resistance system that is induce d by the presence of CAMPs. It is proposed that the RosA/RosB system protec ts the bacteria by both acidifying the cytoplasm to prevent the CAMPs actio n and pumping the CAMPs out of the cell.