Pregnant ewes were vaccinated with partially purified, cell-free K99 antigen isolated from an enteropathogenic strain of , strain B41 (O101:K99:NM), to induce passive immunity the colostrum in their off-spring against an oral challenge with heterologous “calf-lamb” entero-pathogenic strains of B44. After sucking their dams, lambs were dosed orally with 7 × 10-2·2 × 10 organisms within 4-21 h of birth. One group of 10 lambs was dosed with cultures of the mucoid (09:K30(A),K99:NM) form of strain B44 and another group of 10 lambs with the non-mucoid (09:K99:NM) form; two groups of four control lambs from unvaccinated dams were similarly challenged. All four control lambs challenged with mucoid B44, but none of 10 lambs from vaccinated dams, developed severe, watery diarrhoea. In the group of lambs challenged with the non-mucoid form of strain B44, loose faeces were detected in only two of the four control lambs and in none of the lambs from vaccinated dams. This suggests that the polysaccharide K antigen may contribute to the virulence of “calf-lamb” enteropathogenic strains that possess the K99 antigen. However, lambs passively immunised with colostrum from dams vaccinated with K99 antigen alone were protected against the production of enteric colibacillosis by oral challenge with EPEC strain B44.


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