Polysaccharide Capsule and Sialic Acid-Mediated Regulation Promote Biofilm-Like Intracellular Bacterial Communities during Cystitis

Abstract

Uropathogenic Escherichia coli (UPEC) is the leading cause of urinary tract infections (UTIs). A murine UTI model has revealed an infection cascade whereby UPEC undergoes cycles of invasion of the bladder epithelium, intracellular proliferation in polysaccharide-containing biofilm-like masses called intracellular bacterial communities (IBC), and then dispersal into the bladder lumen to initiate further rounds of epithelial colonization and invasion. We predicted that the UPEC K1 polysaccharide capsule is a key constituent of the IBC matrix. Compared to prototypic E. coli K1 strain UTI89, a capsule assembly mutant had a fitness defect in functionally TLR4؉ and TLR4 ؊ mice, suggesting a protective role of capsule in inflamed and noninflamed hosts. K1 capsule assembly and synthesis mutants had dramatically reduced IBC formation, demonstrating the common requirement for K1 polysaccharide in IBC development. The capsule assembly mutant appeared dispersed in the cytoplasm of the bladder epithelial cells and failed to undergo high-density intracellular replication during later stages of infection, when the wild-type strain continued to form serial generations of IBC. Deletion of the sialic acid regulator gene nanR partially restored IBC formation in the capsule assembly mutant. These data suggest that capsule is necessary for efficient IBC formation and that aberrant sialic acid accumulation, resulting from disruption of K1 capsule assembly, produces a NanR-mediated defect in intracellular proliferation and IBC development. Together, these data demonstrate the complex but important roles of UPEC polysaccharide encapsulation and sialic acid signaling in multiple stages of UTI pathogenesis.

Transposon Mutagenesis Identifies Uropathogenic Escherichia coli Biofilm Factors

“…In addition to type 1 pili, sialic acid capsule has been implicated in IBC formation and UPEC virulence (3). Recent studies have identified the QseC sensor kinase as another IBC effector, as qseC deletion indirectly impacts expression of type 1 pili and interferes with biofilm formation (25,37).…”

“…Eighty-five percent of community-acquired urinary tract infections (UTI) and 50% of device-associated UTI are caused by uropathogenic Escherichia coli (UPEC) (24), which employ a complex pathogenic cascade in the urinary tract, occupying extracellular and intracellular niches during the course of infection (60). UTI studies in mouse models have identified numerous virulence factors, including adhesins, toxins, iron acquisition systems, capsular structures, flagella, pathogenicity islands, and factors important for biofilm formation (3,26,28,(69)(70)(71). UPEC strains have genes that encode a multitude of chaperone/usher pathway (CUP) pili (14,16,35,45,64).…”

The Catabolite Repressor Protein-Cyclic AMP Complex Regulates csgD and Biofilm Formation in Uropathogenic Escherichia coli

“…Once in the bladder, E. coli utilizes type 1 pili to invade bladder epithelial cells (11). E. coli bacteria then form a biofilm-like structure known as an intracellular bacterial community (IBC), and cells are coated by the ECM component K1 for protection from host cell recognition (12). The ability of E. coli to recognize multiple environments is critical for production of various UTI-related appendages at the various stages of UTI and IBC formation.…”

Molecular Characterization of the Vacuolating Autotransporter Toxin in Uropathogenic Escherichia coli

“…Uropathogenic Escherichia coli (UPEC) strains are the primary etiological agent of UTIs and cause 70 to 90% of all such infections (2). UPEC can survive in the urinary tract and cause disease due to a diverse range of virulence factors, including fimbriae (3-6), autotransporter (AT) proteins (7)(8)(9)(10), surface polysaccharides, such as the O antigen and capsule (11)(12)(13), iron acquisition systems (14)(15)(16), and toxins (17)(18)(19)(20)(21).…”