Escherichia coli O157:H7 virulence factors differentially impact cattle and bison macrophage killing capacity.

ABSTRACT

Enterohemorrhagic Escherichia coli O157H7 colonizes the gastrointestinal tract of ruminants, including cattle and bison, which are reservoirs of these zoonotic disease-causing bacteria. Healthy animals colonized by E. coli O157H7 do not experience clinical symptoms of the disease induced by E. coli O157H7 infections in humans; however, a variety of host immunological factors may play a role in the amount and frequency of fecal shedding of E. coli O157H7 by ruminant reservoirs. How gastrointestinal colonization by E. coli O157H7 impacts these host animal immunological factors is unknown. Here, various isogenic mutant strains of a foodborne isolate of E. coli O157H7 were used to evaluate bacterial killing capacity of macrophages of cattle and bison, the two ruminant species. Cattle macrophages demonstrated an enhanced ability to phagocytose and kill E. coli O157H7 compared to bison macrophages, and killing ability was impacted by E. coli O157H7 virulence gene expression. These findings suggest that the macrophage responses to E. coli O157H7 might play a role in the variations observed in E. coli O157H7 fecal shedding by ruminants in nature.