Differential invasive capacity of Providencia alcalifaciens isolates

About This Grant

PROJECT SUMMARY The bacterial family that is particularly associated with infections of the gut are Enterobacteriaceae. One significant but understudied family member, Providencia alcalifaciens, has been linked to sporadic foodborne outbreaks of diarrhea and isolated from stool samples from persons with diarrhea. P. alcalifaciens is also part of the human oral, sputum and gut microbiomes of healthy individuals. What distinguishes commensal from enteropathogenic P. alcalifaciens? Most diarrheal isolates harbor a large plasmid ranging in size from 128 kb - 181 kb that encodes a type III secretion system (T3SS) that is closely related to, and functionally interchangeable with, the invasion-associated T3SS (T3SS1) of Salmonella enterica serovar Typhimurium. Of the plasmid- carrying isolates, a subset invades non-phagocytic host cells in cellulo. The primary objective of this application is to define what role this genomic and phenotypic heterogeneity plays in P. alcalifaciens pathogenesis. A comparative genomic analysis identified nine genes in the 40 kb type III gene cluster on the plasmid as statistically associated with the invasion phenotype. In Specific Aim 1, we will use in silico, in vitro and in cellulo analysis to determine if these predicted genes are the molecular drivers of invasiveness in P. alcalifaciens. In Specific Aim 2, we will establish an oral-challenge murine model to assess bacterial colonization and host response in the gut upon infection with invasive and non-invasive P. alcalifaciens isolates. These results will define the contribution of intestinal epithelial cell invasion to P. alcalifaciens enteropathogenesis via the natural route of infection. The potential impact of our proposed work is high because it will be the first to decipher the genetic and molecular basis of pathogenicity of P. alcalifaciens, and the first systematic assessment of P. alcalifaciens virulence determinants in a small animal model.