In pig industry verocytotoxic Escherichia coli (VTEC) strains, in particular O138, O139 and O141 serogroups, cause severe entetoxemias in weaned piglets and are responsible of important economic losses. Novel strategies are required to control VTEC infection, considering that actually no vaccines are
available and an outbreak of the disease requires antibiotic medication. The aim of this study was to evaluate edible vaccines represented by transgenic tobacco seeds, previously engineered for the seed-specific expression of B subunit of VT2e toxin and F18 adhesive fimbriae of VTEC strain as described by Rossi et al. 2003, in weaned piglets.
A total of 43 weaned piglets were randomized into 4 groups. Three immunized groups T1, T2, T3 received a bolus of tobacco seeds (TS) mixed with chocolate by oral route on days 0, 1, 2, 14 of the trial. In particular T1 received 10 grams of TS-F18 and 10 grams of TS-VT2e-B , T2 received 10 grams of TS-VT2e-B and T3 received 25 grams of TS-VT2e-B . Control Group (CG) received 20g of wild type TS. In this immunization phase faecal and blood samples were collected weekly to evaluate IgA and IgG amount by ELISA assays. On day 22, piglets were challenged with 1x1010 ufc of O138 E. coli strain. Faecal score, body temperature, clinical signs related to Oedema Disease were determined, daily for 15 days after challenge. Zootechnical performances and haematocrit percentage ( HT) were evaluated during the experimental period.
T1, receiving both the antigens, showed a higher level of IgA in faeces than other groups on day 21 (220±130 ng/ml vs control group: 72.2±30.34ng/ml). No differences were observed among groups in relation to total IgG titer in feces and total IgA and IgG levels in serum. For each clinical sign, the average total score was
significantly higher in the control group compared to orally immunized groups and T1, T2 and T3 showed a faster recovery than CG. After challenge average daily gain and feed intake were higher in T1 and T2 than CG. No differences were observed between T2 and T3, for all measured parameters, suggesting that no dose-response effect was evidenced for Vt2e-B antigen in our experimental conditions.
We showed that oral administration of recombinant tobacco seeds expressing antigenic proteins against VTEC strains can induce an increase of mucosal antibodies and a protective effect against the challenge strain in piglets.
L Rossi, G Poli, V Sala, S Vagni , S Careno, A Baldi, C Fogher. Oral immunization of weaned piglets with tobacco seeds expressing antigenic proteins of verocytotoxic Escherichia coli strains. IPVS, 2012.