Pathways to Heterogeneity in Uropathogenic Escherichia coli

Abstract

Infectious diseases often result from invasive bacteria that replicate within specific anatomical sites. The replication of these bacteria provokes immune responses, inflammation, and contributes to the onset of various disease symptoms. While traditionally, disease-promoting bacterial populations arising from a single progenitor were thought to be uniform in genotype and phenotype, this notion has been over-turned in recent years Variations in the microenvironment, including metabolic factors and stress-inducing cues, exert selective pressure on mixed isogenic bacterial populations, favoring phenotypes that enhance colonization. In this work, I investigate one such example of heterogeneity in this thesis dissertation, using uropathogenic Escherichia coli (UPEC), the predominant cause of urinary tract infections worldwide. Recurrent UTIs (rUTI) – which affect approximately 25% of women who experience a primary UTI – are primarily fueled by UPEC reservoirs established in the host. The contribution of heterogeneity to reservoir formation and recurrent UTI remains poorly understood. This dissertation focuses on an example of UPEC heterogeneity, identified in strains isolated from rUTI patients. I report a “peppermint” heterogeneous phenotype strain that results from differential expression of exopolymeric substances in UPEC colonies and subsequent differential uptake of the Congo red dye. Following the isolation of peppermint subpopulations, next-generation sequencing revealed a regulatory network controlling curli and cellulose, the exopolymeric substances that bind Congo red in E. coli. Moreover, I report that the subpopulations isolated during this thesis work have differing colonization potentials in reservoir niches, specifically nlpI- and waaO- deficient mutants. My work emphasizes the characterization of heterogeneous clinical UPEC morphotypes and their implications as a potential source for UPEC persistence.