Citrobacter rodentium possesses a functional Type II Secretion System necessary for successful host infection

Infectious diarrheal diseases are the second leading cause of mortality in young children, many of which are driven by Gram-negative bacterial pathogens. To establish successful host infections these pathogens employ a plethora of virulence factors necessary to compete with the resident microbiota, and evade and neutralize the host defences. The type II secretion system (T2SS) is one such conserved molecular machine which allows for the delivery of effector proteins into the extracellular milieu. To explore the role of the T2SS during natural host infection, we used Citrobacter rodentium, a murine enteric pathogen, as a model of human intestinal disease caused by pathogenic Escherichia coli such as Enteropathogenic E. coli (EPEC). In this study, we identify that the C. rodentium genome carries one T2SS and 22 potential T2SS-secreted protein effectors, as predicted via sequence homology. We demonstrated that this system was functional in vitro, identifying a role in intestinal mucin degradation allowing for its utilization as a carbon source, and enhancing C. rodentium attachment to a mucus-producing colon cell line. During host infection, loss of the T2SS or associated effectors led to a significant colonization defect and lack of systemic spread. In mice susceptible to lethal infection, the T2SS mutant strain was strongly attenuated, displaying reduced morbidity and mortality. Together these data highlight the important role of a functional T2SS and its effector repertoire in C. rodentium pathogenesis, aiding in successful host mucosal colonization.