Characterization of porcine-specific surface (S-) layer protein carrying Lactobacillus species, S-layer proteins and the adhesin of Escherichia coli F18 fimbriae : Potential applications for veterinary medicine

Abstract

Lactobacilli, common members of porcine intestinal microbiota, have been considered to be an important group of bacteria in maintaining the stability of gastrointestinal tract (GIT), preventing intestinal infections and supporting intestinal health. Because several species of lactobacilli have GRAS (generally regarded as safe) status and some of them have an ability to interact with intestinal epithelial cells, their possible applications as mucosal vaccine vector and/or probiotics have aroused interest. Selection criteria for lactobacilli to be used as vaccine vector or probiotic include the abilities to adhere to the intestinal epithelium cells and colonize the lumen of the GIT. Bacterial adhesins are often found in hair-like appendages called pili or fimbriae that extend outward from bacterial surface. Alternatively, they can be directly associated with the microbial cell surface. Surface layer proteins (Slps) of lactobacilli have been shown to confer tissue adherence. In this study, S-layer carrying lactobacilli from the intestine and faeces of pigs were isolated and their ability to adhere was studied. Besides the putative binding properties of Slps, a very large number of Slp subunits present in an S-layer make the use of the S-layer structure a very interesting alternative to surface display antigens. Therefore, the aim was to characterize the S-layer proteins. Two new surface layer proteins with potential to be tested as antigen carriers were characterized, and three slp genes were isolated, sequenced, and studied for their expression. To identify the S-layer carrying lactobacilli strains of porcine origin, a polyphasic taxonomic approach was applied. These results indicated that strains from Finland and the related L. sobrius strains, originating from elsewhere, constitute a single species, L. amylovorus, and that the name L. sobrius should be considered as a later synonym of L. amylovorus. The F18 fimbriae carrying Escherichia coli strains cause post-weaning diarrhoea and edema disease in pigs. The adhesin FedF of E. coli F18 fimbriae was characterized. The work aims at developing lactobacilli as a live mucosal vaccine vector for pigs against diseases caused by F18+ E. coli. Oral immunization of weaned piglets with adhesins is known to induce a protective mucosal immune response. Naked FedF appeared to be very unstable but we could produce it as a fusion protein with maltose binding protein (MBP). Specific adhesion to isolated porcine intestinal epithelial cells was demonstrated with MBP-FedF fusions as well as the ability of anti-MBP-FedF antibodies to prevent binding of E. coli F18 to porcine epithelial cells.

Julkaistaan myöhemmin