The overall project goal was to determine mechanisms of intestinal colonization of STEC O26, O45, O103, O111, O121, and O145 to provide a basis for development of new and improved pre-harvest interventions for these organisms. The supporting objectives were to compare STEC O26, O45, O103, O111, O121, and O145 isolates of varying flagellar and intimin type composition for adherence and attaching-effacing lesions in: 1) mucosal explants; and 2) primary epithelial cell cultures; both from the bovine small (SI) and large intestine (LI).
Non-O157 STEC strains from all six serogroups currently classified as adulterants in raw non-intact beef (O26, O45, O103, O111, O121, and O145) expressing different flagellar types (e.g., H2, H10, H11, H16, H19, H21, and H28) and variants of intimin, viz., ?1, ?, ?, and ?1, adhered to bovine colonic epithelium and induced the formation of attaching-effacing lesions. Non-O157 STEC strains lacking intimin were also shown to adhere to bovine colonic epithelium; hence, must utilize other mechanisms for attachment. Most strains expressing flagella were motile and some, e.g., O45:H2, O103:H2, and O103:[H11] were shown to adhere to intestinal mucus and epithelial cells via their flagella; hence, flagella appear to play an important role in the early steps of intestinal colonization by non-O157 STEC. Some non-O157 strains, particularly an O103:H2 strain, were found to invade bovine and human intestinal epithelial cells, which may represent a relatively unknown mechanism of colonization of these organisms. Additional adherence studies were conducted with an enteroaggregative STEC O104:H4 strain that caused a large foodborne epidemic attributable to a non-beef source in Germany in the summer of 2011. These studies showed this strain has the ability to adhere to bovine colonic epithelium and may do so via aggregative adherence fimbria. Hence, surveillance studies to address the possibility that this strain is carried by cattle should be continued.
This research demonstrates that interventions that block the effects of flagella, intimin, and other adherence mechanisms in non-O157 STEC may be effective for pre-harvest control of non-O157 STEC in cattle.