Pili in microspheres protect rabbits from diarrhoea induced by E. coli strain RDEC-1

We tested whether pilus proteins of rabbit diarrhoeagenic Escherichia coli (RDEC-1), incorporated into biodegradable microspheres, could function as safe and effective oral immunogens in the rabbit diarrhoea model. The RDEC-1 adhesin, AF/R1, incorporated into poly(D,L-lactide-co-glycolide) microspheres, was administered intraduodenally. Vaccinated and unvaccinated rabbits were challenged with RDEC-1 and killed 1 week later. Vaccination with AF/R1 in microspheres did not cause diarrhoea or weight loss. After challenge, rabbits given AF/R1 in microspheres, in contrast to unvaccinated animals, remained in good health. RDEC-1 attachment to caecal epithelium of vaccinated rabbits was reduced (p = 0.02), whereas numbers of RDEC-1 in intestinal fluids were little affected. Also, in vaccinated animals, biliary anti-AF/R1 IgA levels were increased, and AF/R1-induced blast-cell transformation was vigorous in spleen cell cultures. We conclude that vaccination with AF/R1 in microspheres was safe and protected rabbits against RDEC-1 disease, probably by interfering with adherence of the bacteria to the intestinal mucosa. The interference might have been due to the presence of specific antibodies secreted in bile.