ORAL IMMUNIZATION IN MICE WITH RECOMBINANT LACTOCOCCUS LACTIS STRAINS PRODUCING A NON-SUPERANTIGENIC VARIANT OF STAPHYLOCOCCAL ENTEROTOXIN B

Giselli Fernandes Asensi (UFRJ); Fabianno Ferreira Dutra (UFRJ); Daniel Ferreira Feijó (UFRJ); Marcelo Torres Bozza (UFRJ); Anderson Miyoshi (UFMG); Yves Le Loir (INRA); Azevedo Vasco Ariston de Carvalho (UFMG); Joab Trajano Silva (UFRJ); Vânia Margaret Flosi Paschoalin (UFRJ)

Staphylococcal enterotoxin B (SEB) is a single chain protein considered an important virulence factor in Staphylococcus aureus. It has a potent superantigenic activity and SEB producing strains are considered as potential biological weapons. Recombinant SEB (rSEB) that lacks any superantigenic activity represents a good vaccine candidate to prevent staphylococcal toxemia. Lactococcus lactis, a foodgrade lactic acid bacterium, is reportedly a good antigen delivery vehicle.  rSEB was produced intra- or extracellularly in L. lactis using pCYT and pSEC plasmids. The resulting recombinant strains were tested as oral live vaccine in mice and the humoral and cellular immune responses were assessed. Groups of 10 male mice C57BL/6 were orally immunized with 10⁹cfu of L. lactis carrying pSEC:rSEB or pCYT:rSEB. Mice vaccinated with the L. lactis carrying the backbone vector alone (pSEC or pCYT) and PBS were used as control. The vaccination schedule included 3 periods of immunization with 3 consecutively days. Serum and stools were collected in order to determine IgG and IgA titers, respectively, by ELISA. Sera were collected at days 14, 28, and 42 after first immunization. Stools from each group were collected at day 15, 24, and 38 after first immunization. These samples are being analyzed. Fifteen days after the last immunization, vaccine efficacy was evaluated by challenging the mice with intraperitoneally administered S. aureus ATCC14458 (SEB producer). Animals were killed 2 weeks after challenge. Splenic clearance of the S. aureus from the animal was analyzed by plating homogenized spleens on Baird Parker (37^oC). Our results showed a significant difference of clearance in mice inoculated with rSEB (L. lactis pCYT:rSEB and pSEC:rSEB) compared to mice that received the PBS control. The number of viable S. aureus recovered from spleens of pCYT:rSEB and pSEC:rSEB groups was 8 and 7 times, respectively, lower than in PBS group. The survival rates were 100% in mice immunized with L. lactis (pCYT:rSEB) and 70% in mice immunized with L. lactis (pSEC:rSEB) whereas, in control groups, it was down to 20% (pSEC), 20% (pCYT) and 10% (PBS). These results are promising and open new perspective for the development of effective strategies against superantigenic toxemia.