The outer membrane (OM) of Gram-negative pathogenic bacteria represents a platform for the secretion and presentation of surface-localized virulence factors.  The conserved periplasmic chaperone SurA ferries nascent OM proteins from the Sec machinery to the BamA OM assembly complex for their final incorporation into the OM.  Our original work demonstrated the importance of SurA in the pathogenesis of urinary tract infections caused by uropathogenic Escherichia coli (UPEC).  Disruption of surA in UPEC leads to deficiency of the OM usher FimD, through which the bacterial cell assembles the adhesive type 1 pili that confer upon UPEC the capacity for bladder epithelial binding and invasion.  We also showed that SurA substrates have an additional role during the post-invasion phase of cystitis, in which UPEC multiply rapidly within bladder epithelial cells to form intracellular bacterial communities (IBCs) and establish a persistent niche within the epithelium, sequestered from host immune defenses and protected from antibiotic killing.  This intraepithelial bacterial reservoir may serve as a seed for recurrent UTI, a common and difficult clinical problem.  Our recent data have identified the UPEC outer membrane protein A (OmpA) as the SurA-dependent factor required for this intracellular phase of cystitis.  Specifically, the UPEC ompA mutant invades bladder epithelium normally, but cannot complete IBC maturation and persist within the uroepithelium.  This pathogenic defect is substantially rescued in mice deficient in Toll-like receptor 4 signaling, suggesting that OmpA modulates host immune mechanisms to promote infection.  In this proposal, we will first define the contribution of OmpA to host innate responses (including neutrophil recruitment and bladder epithelial exfoliation) and to adaptive responses.  We will subsequently resolve whether OmpA confers protection against the antipathogen activity of neutrophils, particularly the action of innate antimicrobial peptides.  Finally, we will use a chromosomal complementation system to determine the structural features of OmpA responsible for the pathogenic phenotypes we have observed.  We anticipate that these studies will validate the SurA substrate OmpA as a central determinant of the intracellular phase of cystitis and inform the development of strategies for interrupting the cycle of recurrence in patients with UTI.  PUBLIC HEALTH RELEVANCE: Many bacteria express surface proteins (called virulence factors) that help the bacteria to cause infectious diseases in humans.  This project aims to determine how one of these bacterial surface proteins, called OmpA, interacts with the human immune system to facilitate the establishment of urinary tract infections.  Understanding the functions of OmpA will lead to new strategies for preventing and treating bacterial infections.