Antibodies Directed against Shiga-Toxin Producing Escherichia coli Serotype O103 Type III Secreted Proteins Block Adherence of Heterologous STEC Serotypes to HEp-2 Cells

Shiga toxin-producing Escherichia coli (STEC) serotype O103 is a zoonotic pathogen that is capable of causing hemorrhagic colitis and hemolytic uremic syndrome (HUS) in humans. The main animal reservoir for STEC is ruminants and hence reducing the levels of this pathogen in cattle could ultimately lower the risk of STEC infection in humans. During the process of infection, STEC(O103) uses a Type III Secretion System (T3SS) to secrete effector proteins (T3SPs) that result in the formation of attaching and effacing (A/E) lesions. Vaccination of cattle with STEC serotype O157 T3SPs has previously been shown to be effective in reducing shedding of STEC(O157) in a serotype-specific manner. In this study, we tested the ability of rabbit polyclonal sera against individual STEC(O103) T3SPs to block adherence of the organism to HEp-2 cells. Our results demonstrate that pooled sera against EspA, EspB, EspF, NleA and Tir significantly lowered the adherence of STEC(O103) relative to pre-immune sera. Likewise, pooled anti-STEC(O103) sera were also able to block adherence by STEC(O157). Vaccination of mice with STEC(O103) recombinant proteins induced strong IgG antibody responses against EspA, EspB, NleA and Tir but not against EspF. However, the vaccine did not affect fecal shedding of STEC(O103) compared to the PBS vaccinated group over the duration of the experiment. Cross reactivity studies using sera against STEC(O103) recombinant proteins revealed a high degree of cross reactivity with STEC(O26) and STEC(O111) proteins implying that sera against STEC(O103) proteins could potentially provide neutralization of attachment to epithelial cells by heterologous STEC serotypes.