Random mutagenesis unveils novel host-pathogen interactions during colonic bacterial infections in immunocompromised hosts

Abstract

Abstract Attaching/Effacing (A/E) pathogens including enteropathogenic Escherichia coli (EPEC), enterohemorrhagic E. coli (EHEC), and the rodent equivalent Citrobacter rodentium (CR) are important causative agents of foodborne diseases. A/E pathogen infections cause severe morbidity and mortality in immunocompromised hosts with low interleukin-22 (IL-22); however, the crucial host-pathogen interactions and the pivotal A/E virulence proteins (effectors) under immunocompromised conditions, remain elusive. We conducted a functional screening of a CR mutant library consisting of ~2,000 mutant strains, generated via transposon-mediated random mutagenesis, and identified several avirulent strains, which abolish CR-induced severe morbidity and mortality in IL-22 knockout (Il22−/−) mice. Recapitulating the attenuated virulence phenotype by the transposon-interrupted mutant strains, genomic deletion of each identified effector in CR dramatically attenuates CR-caused lethality in Il22−/− mice. Interestingly, genetic deletion of each identified effector gene in CR genome exhibits no impact on the colonization and proliferation of CR in the infected animals; however, the deficiencies in these effectors substantially impede the colonic inflammatory response in the CR-infected Il22−/− mice, through distinct cellular and molecular mechanisms. Hence, our findings unveil a set of novel A/E pathogen effectors pathologically relevant to the severe morbidity and mortality in Il22−/− animals, which could provide new strategies to control A/E pathogen infections under the low IL-22 immunocompromised conditions, which are frequently associated with chronic HIV infection, organ transplantation, and other diseases.