Dissecting virulence: Systematic and functional analyses of a pathogenicity island

TLDR

Bacterial pathogenicity islands encode effector proteins and secretion systems, and the LEE PAI is present in EHEC, EPEC, and Citrobacter rodentium. The authors systematically mutagenized all 41 CR LEE genes and evaluated the resulting mutants in vitro and in a mouse infection model. The study uncovered 33 virulence factors—including two regulators and a hierarchical type III secretion switch—identified seven non‑LEE effectors encoded by three uncharacterized PAIs in EHEC O157 that cooperate with the LEE, providing new insights into bacterial virulence mechanisms.

Abstract

Bacterial pathogenicity islands (PAI) often encode both effector molecules responsible for disease and secretion systems that deliver these effectors to host cells. Human enterohemorrhagic Escherichia coli (EHEC), enteropathogenic E. coli , and the mouse pathogen Citrobacter rodentium (CR) possess the locus of enterocyte effacement (LEE) PAI. We systematically mutagenized all 41 CR LEE genes and functionally characterized these mutants in vitro and in a murine infection model. We identified 33 virulence factors, including two virulence regulators and a hierarchical switch for type III secretion. In addition, 7 potential type III effectors encoded outside the LEE were identified by using a proteomics approach. These non-LEE effectors are encoded by three uncharacterized PAIs in EHEC O157, suggesting that these PAIs act cooperatively with the LEE in pathogenesis. Our findings provide significant insights into bacterial virulence mechanisms and disease.