Common pili promote the fitness and virulence of a hybrid aEPEC/ExPEC strain within diverse host environments.

Pathogenic subsets of include diarrheagenic (DEC) strains that cause disease within the gut and extraintestinal pathogenic (ExPEC) strains that are linked with urinary tract infections, bacteremia, and other infections outside of intestinal tract. Among DEC strains is an emergent pathotype known as atypical enteropathogenic (aEPEC), which can cause severe diarrhea. Recent sequencing efforts revealed that some strains possess genetic features that are characteristic of both DEC and ExPEC isolates. BA1250 is a newly reclassified hybrid strain with characteristics of aEPEC and ExPEC. This strain was isolated from a child with diarrhea, but its genetic features indicate that it might have the capacity to cause disease at extraintestinal sites. The spectrum of adhesins encoded by hybrid strains like BA1250 are expected to be especially important in facilitating colonization of diverse niches. (ECP) is an adhesin expressed by many pathogens, but how it impacts hybrid strains has not been ascertained. Here, using zebrafish larvae as surrogate hosts to model both gut colonization and extraintestinal infections, we found that ECP can act as a multi-niche colonization and virulence factor for BA1250. Furthermore, our results indicate that ECP-related changes in activation of envelope stress response pathways may alter the fitness of BA1250. Using an approach, we also delineated the broader repertoire of adhesins that are encoded by BA1250, and provide evidence that the expression of at least a few of these varies in the absence of functional ECP.