Understanding the Evolution of Extra-Intestinal Pathogenic Escherichia coli (ExPEC) Via Genetic Analysis of Capsular Prevalence Among Clinical Isolates and the Role of Sialic Acid in ExPEC Niche Specificity

Abstract

Our purpose was to gain knowledge of the bacterial demographic using recently isolated strains causing uncomplicated UTI; we also sought to understand how capsular type has changed over time. Using multiplex PCR, data show Group 2 encapsulated strains have significantly increased in uncomplicated UTI in the past twenty years, suggesting an expansion of previously under-represented capsule types. Additionally, we find K1 encapsulated extra-intestinal pathogenic Escherichia coli (ExPEC) are significantly associated with symptomatic UTI.K1 ExPEC are able to catabolize sialic acid for energy (glycolysis), and membrane production (LPS and peptidoglycan), as well as synthesize sialic acid for capsule expression. NanR is an ExPEC global regulator of known virulence factors, however regulation via NanR is controlled by sialic acid. Using an established murine model, fluorescent microscopy, high performance liquid chromatography, and tissue culture methods, we find K1 ExPEC use sialic acid as a signaling molecule to determine location within the host.Capsule and Type-1 pili (T1P) are important for ExPEC pathogenesis, both in the urinary tract and in more disseminated disease; coordinated regulation of these two virulence factors has been implicated. Using a tissue culture model, Western blot analysis, T1P agglutination and reporter assays, we found capsule and T1P are counter-regulated, and that this mechanism is conserved in non-pathogenic E. coli.