UNLABELLED

To eradicate bacterial pathogens, neutrophils are recruited to the sites of infection, where they engulf and kill microbes through the production of reactive oxygen and chlorine species (ROS/RCS). The most prominent RCS is antimicrobial oxidant hypochlorous acid (HOCl), which rapidly reacts with various amino acids side chains, including those containing sulfur and primary/tertiary amines, causing significant macromolecular damage. Pathogens like uropathogenic (UPEC), the primary causative agent of urinary tract infections (UTIs), have developed sophisticated defense systems to protect themselves from HOCl. We recently identified the RcrR regulon as a novel HOCl defense strategy in UPEC. The regulon is controlled by the HOCl-sensing transcriptional repressor RcrR, which is oxidatively inactivated by HOCl resulting in the expression of its target genes, including . encodes the putative membrane protein RcrB, deletion of which substantially increases UPEC's susceptibility to HOCl. However, many questions regarding RcrB's role remain open including whether the protein's mode of action requires additional help, expression is induced by physiologically relevant oxidants other than HOCl, and expression of this defense system is limited to specific media and/or cultivation conditions. Here, we provide evidence that RcrB expression is sufficient to 's protection from HOCl and induced by and protects from several RCS but not from ROS. RcrB plays a protective role for RCS-stressed planktonic cells under various growth and cultivation conditions but appears to be irrelevant for UPEC's biofilm formation.

IMPORTANCE

Bacterial infections pose an increasing threat to human health exacerbating the demand for alternative treatment options. UPEC, the most common etiological agent of urinary tract infections (UTIs), are confronted by neutrophilic attacks in the bladder, and must therefore be well equipped with powerful defense systems to fend off the toxic effects of RCS. How UPEC deal with the negative consequences of the oxidative burst in the neutrophil phagosome remains unclear. Our study sheds light on the requirements for the expression and protective effects of RcrB, which we recently identified as UPEC's most potent defense system towards HOCl-stress and phagocytosis. Thus, this novel HOCl-stress defense system could potentially serve as an attractive drug target to increase the body's own capacity to fight UTIs.