Isotype-specific antibody responses against <i>Escherichia coli </i>O157:H7 locus of enterocyte effacement proteins in adult beef cattle following experimental infection

Escherichia coli O157:H7 is an important food-borne pathogen and cause of hemorrhagic colitis and hemolytic uremic syndrome in humans. Cattle are an important reservoir of E. coli O157:H7, in which the organism colonizes the intestinal tract and is shed in the feces. Vaccination of cattle has signifi cant potential as a pre-harvest intervention strategy for E. coli O157:H7; however, basic information about the bovine immune responses to important bacterial colonization factors resulting from infection has not been reported. The serum and fecal IgG and IgA antibody responses of adult cattle to E. coli O157:H7 intimin, translocated intimin receptor (Tir), E. coli-secreted proteins (Esp)A, EspB and O157 lipopolysaccharide (LPS) in response to infection were determined. All animals were seropositive for all fi ve antigens prior to inoculation, with antibody titers to EspB and O157 LPS signifi cantly higher (P < 0.05) than those to Tir, intimin and EspA. After inoculation, the cattle became colonized and developed signifi cant increases in their serum antibody titers to intimin, Tir, EspB, EspA and O157 LPS (P < 0.05); however, by 42 days post-inoculation the titers to all except EspB were on the decline. In contrast, preand post-inoculation fecal IgG and IgA antibodies to these same antigens were not detected (<1:5). These results indicate that cattle respond serologically to E. coli O157:H7 type III secreted proteins, intimin and O157 LPS during the course of infection and the response is correlated with the extent of fecal shedding.