Evaluation of the prophylactic potential of non-enterotoxigenic Escherichia coli (non-ETEC) vaccine immunization and dietary mannan oligosaccharide competitive exclusion benefits against ETEC infections in weaned pigs

Abstract

Enterotoxigenic Escherichia coli (ETEC) strains expressing F4 and F18 fimbriae are the most common causative agents of post-weaning diarrhoea (PWD) in pigs. The growing global restriction on the use of antibiotics in food animals has encouraged research into the development of nutritional and feeding strategies as well as vaccination against PWD. The aim of this study was to evaluate the efficacy of a live oral F4ac+ F18ac+ non-ETEC vaccine candidate (VAC) to stimulate gut and systemic cellular immunity in 4-week old pigs over 5 weeks following immunization. The onset and duration of protective immunity against on-farm occurring PWD, growth performance, diarrhoea scoring and mortality, as well as the phenotypic proportions of immune cells, were determined. Faecal and ileal samples were taken for determining the microbial composition or phenotyping of naïve/memory T cells. Also, the effect of prebiotic supplement mannan oligosaccharide (MOS) in the prevention of small intestinal colonization by ETEC, and its potential adjuvanticity in combination with the vaccine (VAC+MOS) were assessed. The pigs supplemented with MOS or that received VAC had significantly higher body weight (BW) (P<0.05) on Day 14, whereas the VAC+MOS treated pigs had significantly lower BW on Day 35. Treatment with VAC+MOS resulted in considerably reduced clinical PWD, in particular the incidence and severity of diarrhoea and mortality. The total bacterial load in the ileum was much lower in the pigs from all 3 principal groups (MOS, VAC, and VAC+MOS) than in the control (CON) group (19 x 107, 17 x 107 and 12 x 107 vs. 23 x 108 CFU/mL, respectively) on Day 35. The pigs from the principal groups had significantly higher proportions of tested immune cells (P<0.05) on Days 28 and 35. The localization and frequency of naive CD45RA+ and memory CD45RC+ T lymphocytes indicated their different distribution patterns within particular tissue structures, such as the villi, crypts, epithelium, lamina propria and areas (interfollicular follicular and Peyer’s patches) of ileal mucosa. This may indicate their different functions in intestinal immune responses to intraluminal microbes and their products, vaccinal immunogens and/or immunomodulators/adjuvants. To conclude, active mucosal immunity is needed to protect pigs against PWD. Hence, oral vaccination of pigs against both F4 and F18 ETEC, in combination with prebiotic supplementation represents a sustainable, practical and effective approach in PWD control.