Bovine Immune Response to Shiga-Toxigenic Escherichia coli O157:H7

ABSTRACT

Although cattle develop humoral immune responses to Shiga-toxigenic (Stx⁺) Escherichia coli O157:H7, infections often result in long-term shedding of these human pathogenic bacteria. The objective of this study was to compare humoral and cellular immune responses to Stx⁺ and Stx⁻ E. coli O157:H7. Three groups of calves were inoculated intrarumenally, twice in a 3-week interval, with different strains of E. coli: a Stx2-producing E. coli O157:H7 strain (Stx2⁺O157), a Shiga toxin-negative E. coli O157:H7 strain (Stx⁻O157), or a nonpathogenic E. coli strain (control). Fecal shedding of Stx2⁺O157 was significantly higher than that of Stx⁻O157 or the control. Three weeks after the second inoculation, all calves were challenged with Stx2⁺O157. Following the challenge, levels of fecal shedding of Stx2⁺O157 were similar in all three groups. Both groups inoculated with an O157 strain developed antibodies to O157 LPS. Calves initially inoculated with Stx⁻O157, but not those inoculated with Stx2⁺O157, developed statistically significant lymphoproliferative responses to heat-killed Stx2⁺O157. These results provide evidence that infections with STEC can suppress the development of specific cellular immune responses in cattle, a finding that will need to be addressed in designing vaccines against E. coli O157:H7 infections in cattle.