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Proc Natl Acad Sci U S A. 2015 Feb 24;112(8):E871-80. doi: 10.1073/pnas.1500374112. Epub 2015 Feb 9.

Dysregulation of Escherichia coli α-hemolysin expression alters the course of acute and persistent urinary tract infection.

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Departments of Molecular Microbiology and Microbial Pathogenesis and.
Pathology and Immunology.
Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E9; and.
Departments of Molecular Microbiology and Microbial Pathogenesis and Department of Pathology, Microbiology, and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232.
Departments of Molecular Microbiology and Microbial Pathogenesis and Center for Women's Infections Disease Research, Washington University School of Medicine, St. Louis, MO 63110;


Urinary tract infections (UTIs) are among the most common bacterial infections, causing considerable morbidity in females. Infection is highly recurrent despite appropriate antibiotic treatment. Uropathogenic Escherichia coli (UPEC), the most common causative agent of UTIs, invades bladder epithelial cells (BECs) and develops into clonal intracellular bacterial communities (IBCs). Upon maturation, IBCs disperse, with bacteria spreading to neighboring BECs to repeat this cycle. This process allows UPEC to gain a foothold in the face of innate defense mechanisms, including micturition, epithelial exfoliation, and the influx of polymorphonuclear leukocytes. Here, we investigated the mechanism and dynamics of urothelial exfoliation in the early acute stages of infection. We show that UPEC α-hemolysin (HlyA) induces Caspase-1/Caspase-4-dependent inflammatory cell death in human urothelial cells, and we demonstrate that the response regulator (CpxR)-sensor kinase (CpxA) two-component system (CpxRA), which regulates virulence gene expression in response to environmental signals, is critical for fine-tuning HlyA cytotoxicity. Deletion of the cpxR transcriptional response regulator derepresses hlyA expression, leading to enhanced Caspase-1/Caspase-4- and NOD-like receptor family, pyrin domain containing 3-dependent inflammatory cell death in human urothelial cells. In vivo, overexpression of HlyA during acute bladder infection induces more rapid and extensive exfoliation and reduced bladder bacterial burdens. Bladder fitness is restored fully by inhibition of Caspase-1 and Caspase-11, the murine homolog of Caspase-4. Thus, we have discovered that fine-tuning of HlyA expression by the CpxRA system is critical for enhancing UPEC fitness in the urinary bladder. These results have significant implications for our understanding of how UPEC establishes persistent colonization.


microbial pathogenesis; persistent colonization; urinary tract infection; uropathogenic E. coli

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