Date of Award

4-30-2024

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Molecular and Cellular Biochemistry Program

First Advisor

Gail Hecht

Second Advisor

Nancy Zeleznik-Le

Abstract

Enteropathogenic E. coli (EPEC) are enteric pathogens that are non-invasive, lack Shiga toxin, and use a type 3 secretion system encoded on the locus of enterocyte effacement (LEE) pathogenicity island to translocate bacterial effector proteins into host intestinal epithelial cells leading to diarrhea. Atypical EPEC (aEPEC), in contrast to typical EPEC (tEPEC), lack bundle-forming pili, likely altering adherence and pathogenicity. Detection of aEPEC with co-infecting pathogens and in some asymptomatic individuals leads to questions regarding aEPEC virulence, especially in adults. I aimed to characterize the clinical manifestations of aEPEC infection and the genetic and in vitro phenotypic factors that contribute to aEPEC virulence. aEPEC are associated with a wide array of symptoms, ranging from asymptomatic carriage to severe diarrhea with up to 10-40 bowel movements/day and persistent/chronic diarrhea in some. Co-infecting pathogens did not alter diarrhea severity. EPEC loads were higher in symptomatic individuals but did not predict diarrhea severity. aEPEC isolates from asymptomatic and symptomatic individuals originated from sporadic infections and diverse lineages. Translocated intimin receptor (Tir), an effector involved in intimate host attachment and actin accumulation under attached bacteria termed pedestals, was a major virulence determinant with Tir subtypes correlating with all examined genetic and in vitro phenotypic virulence factors. Principal component analyses revealed distinct clusters of aEPEC isolates based on virulence determinants. The most virulent aEPEC isolates were characterized by having the greatest homology to tEPEC/EHEC in EspA, an adhesin and needle protein, and the least homology in Tir and other LEE effectors. These isolates also had the greatest number of non-LEE effectors and adhesins, the greatest adherence and pedestal formation on intestinal epithelial cells, and most robust diarrheal symptoms and severity. The least virulent aEPEC isolates had the opposite genetic and phenotypic virulence factors. Those isolates with variable genetic virulence factors correspondingly had variability in phenotypic and clinical manifestations. A subset of aEPEC isolates originating from symptomatic individuals did not fit this trend and likely possess unique pathogenic mechanisms. This is the first study to correlate in vitro phenotypes and clinical manifestations with genetic virulence factors of aEPEC isolates from children and adults in the US.

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