Antibody responses elicited in mice immunized with Bacillus subtilis vaccine strains expressing non toxic Stx2 (Stx2ÄAB) form producing by enterohaemorragic Escherichia coli O157:H7.

GÓMEZ PADP; BENTANCOR LV; ROJAS RLG; SBROGIO-ALMEIDA ME; PALERMO MS; FERREIRA LCS; FERREIRA RCC

Buenos Aires

Simposio; 7th International Symposium on Shiga -Toxin (Verocytotoxin)- Producing Eschericchia coli (VTEC2009); 2009

Asociación Argentina de Microbiología

Shiga toxin (Stx)-producing Escherichia coli strains (STEC) cause diarrhea, hemorrhagic colitis and, in some cases, the Hemolytic Uremic Syndrome (HUS), a life-threatening illness characterized by acute renal failure, microangiopathic hemolytic anemia and thrombocytopenia. No effective vaccine or immunotherapy is presently available.  The toxin comprises a single catalytic A subunit, endowed with protein synthesis inhibition activity associated with the N-glycosidase activity, and five B subunits, involved in the binding to the Gb3 glycolipid receptor on the surface of the target cells. The use of life recombinant Bacillus subtillis strains, a harmless spore former gram-positive bacterium species as a vaccine vehicle for the delivery of Stx represents an interesting and not previously tested immunization approach against HUS. In this study we report the construction of B. subtilis recombinant strains expressing a mutated Stx2 composed of the B subunit plus the A2 subunit (Stx2ÄAB) under the control of stress inducible B. subtilis PgsiB promoter. Immunization assays using BALB/c mice were performed using subcutaneous routes with both vegetative cells and spores of the recombinant B. subtilis vaccine strain. Mice immunized via the subcutaneous route with spores, but not those immunized with vegetative cells, developed specific anti-Stx2ÄAB serum IgG. Nonetheless, serum anti-Stx2ÄAB antibodies raised in mice immunized with the recombinant B. subtilis strain did not inhibit the toxic effects of the native toxin, both under in vitro and in vivo conditions, suggesting that either the quantity or the quality of the induced immune response did not support an effective neutralization of Stx2 produced by EHEC strains. The results indicate that alternative expression system including codon usage adaptation or incorporation of strong adjuvants will be required for the generation of effective vaccine formulations active against HUS based on recombinant B. subtilis strains. Financial Support:  Fapesp and Capes