Date of Award

9-17-2024

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Molecular Microbiology & Microbial Pathogenesis)

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

Urinary tract infections (UTI) are an extremely common affliction affecting 150 million people worldwide each year. UTIs are a leading cause of antibiotic therapy among otherwise healthy adult women, accounting for 15% of all outpatient antibiotic prescriptions. Uropathogenic Escherichia coli (UPEC) cause over 80% of community-acquired UTIs. Even when infection is cleared from the urine by clinical antibiotic regimens, 27% of women will experience recurrent UTI (rUTI) within months. Greater than 60% of rUTIs are caused by the same strain of E. coli that caused the initial infection, suggesting that one or more host-associated reservoirs of UPEC can re-inoculate the urinary tract in susceptible women. The intestine is one such reservoir, with its resident microbiota acting as a major reservoir from which UPEC can be shed to seed colonization of the lower urogenital tracts and urinary tract. A comprehensive strategy for reducing the rate of rUTI incidence should therefore include a component which targets the intestinal reservoir of UPEC. However, the mechanisms underpinning UPEC colonization and persistence within the gut are not well understood. In 2017, Caitlin Spaulding in the Hultgren lab identified two pili (Type 1 and F17-like) which promote UPEC intestinal colonization and found that UPEC can be depleted simultaneously from the mouse intestine and the bladder by blocking the interaction between the FimH adhesin of type 1 pili and its ligand mannose. Type 1 and F17-like pili are part of the family of Chaperone-Usher Pathway (CUP) pili, which are carried by UPEC isolates and typically mediate binding to glycans on host surfaces. UPEC colonizes the mouse colon and E. coli is can grow well within secreted mucus layers of the large intestine. However, the specifics of how E. coli achieves colonization of mucus is unclear since mucus is continuously secreted and turned over at a rapid pace. For my doctoral research, I started by localizing the binding of adhesins from a set of CUP pili (Type 1, F17-like, Yeh, and Yhl) and found that while several promoted binding to the colon contents, only FimH enabled binding to secreted mucus. Using the clinical UPEC isolate UTI89, I went on to show that deleting the FimH adhesin from UTI89 decreased association with colon mucus in vivo. Notably, UTI89Δfim upregulated flagella which permitted motility and infiltration through the normally inner mucus layer of the distal colon ex vivo, which is normally impenetrable to bacteria under conditions of homeostasis, and this was also observed in another clinical UTI isolate CFT073. This suggests that flagellar-mediated motility may contribute to UPEC access to the continuously secreted mucus habitat. Through my localization studies, I also made the discovery that F17-like and Yeh pili bind primarily to ligands within the intestinal lumen, and not the mucosa. These findings lay the groundwork for further understanding the contribution of luminal rather than mucosal ligands on UPEC intestinal colonization, which remains an unexplored area of research. Another key component of understanding the basis for UPEC intestinal colonization is to determine whether particular bacteria taxa within the intestine promote or inhibit UPEC colonization. The mouse intestine is intrinsically resistant to colonization by E. coli unless pre-treated with the antibiotic streptomycin, a phenomenon deemed ‘colonization resistance’. I leveraged alterations in the timing of streptomycin administration prior to UTI89 inoculation to generate microbiotas with different levels of colonization resistance, and subsequently used metagenomic sequencing to relate microbial composition to UTI89 intestinal colonization. Using this method, I was able to identify a set of bacteria whose absence is specifically correlated with the presence of UTI89. Interestingly, depletion of the Blautia is associated with UTI89 in the mouse gut and were also found to be depleted at time of UTI in fecal isolates from a clinical cohort comparing the microbiota of healthy vs. rUTI women. Blautia is therefore a candidate for a potential probiotic strain which could provide colonization resistance to UPEC in the intestine, although more research is needed to establish causality. This dissertation provides key insights into the mechanisms of UPEC intestinal colonization, mucosal association and potential strategies for depletion of this important reservoir.

Language

English (en)

Chair and Committee

Scott Hultgren

Committee Members

Andrew Kau; David Hundstad; Matthew Ciorba; Megan Baldridge

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Microbiology Commons

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