An experimental vaccine against E. coli O157:H7 for cattle composed by Intimin, EspB and Stx2B.

IBARRA CRISTINA; GARBACCIO SERGIO; PALERMO MARINA; VILTE DANIEL; MARTORELLI LUISINA; CATALDI ANGEL; ALBANESE ADRIANA; FIORENTINO GABRIELA

Foz de Iguazú-Paraná

Congreso; 29º Congreso Brasilero de Microbiología; 2017

Sociedad Brasilera de Microbiología

Escherichia coli O157:H7 is a zoonotic pathogen of global importance and the serotype most frequently associated with cases of Hemolytic Uremic Syndrome. The main reservoir of this pathogen is bovine cattle.Our group has demonstrated that vaccination with the carboxy-terminal fraction of Intimin γ (IntC280) and EspB can reduce fecal shedding of E. coli O157:H7. Furthermore, Stx2 has been shown to exert a local immunosuppressive effect on the bovine intestine, so an immune response against the toxin could improve the protective ability of the vaccine. In a previous work, we have demonstrated that vaccination of cattle with Stx2B fused to Brucella Lumazine Synthase (BLS-Stx2B) induces humoral immune response able to neutralize Stx2 cytotoxicity in Vero cells in vitro.The objective of this work is to determine the protective efficacy in terms of fecal shedding after experimental challenge, in calves vaccinated with IntC280, EspB and BLS-Stx2B. To this end, 15 3-month-old male Holando Argentino calves were immunized as follows: EspB + IntC280 (n = 5); EspB + IntC280 + BLS-Stx2B (n = 5); Control (n = 5). Animals received two doses with 100 μg of IntC280 and EspB and 300 μg of BLS-Stx2B, separated by 15 days. Blood samples were taken periodically to evaluate the humoral immune response. At 24 days post immunization (dpi), calves were intragastrically challenged with 109 CFU of E. coli O157:H7. Shedding of E. coli O157:H7 was followed in recto-anal mucosal swabs by direct plating and enrichment followed by immunomagnetic separation. Subsequent multiplex PCR was performed to confirm the presence of EHEC O157:H7.Vaccination generated a significant increase in the level of specific antibodies against IntC280 and EspB in both groups, and against Stx2B in the group that received the 3 antigens. Furthermore, the antibodies against Stx2B showed neutralization of Stx2 cytotoxicity in Vero cells after 15 dpi, significantly different from the control group and from animals vaccinated with 2 antigens. Both vaccine formulations induced a protective response reducing the shedding of E. coli O157:H7 compared to the control group. However, the addition of Stx2B to the vaccine formulation did not induce greater protection than the protection conferred by IntC280 and EspB alone.In conclusion, despite a significant humoral response against Stx2B with neutralizing ability of Stx2 in vitro was elicited in calves vaccinated with this antigen, no further increase in protection was observed when compared with the group that received only 2 antigens. Based on this evidence it is necessary to pursue the search for alternatives that improve the elicitation of immune responses against Stx2 in order to reduce the colonization of the bovine gastrointestinal tract by these zoonotic bacteria.