Immunological cross-reactivity between the vaccine and other isolates of Streptococcus bovis and Lactobacillus

Recent studies have showed that immunisation with Streptococcus bovis (Sb-5 ) and Lactobacillus (LB-27) may confer protection against lactic acidosis i n sheep and cattle. The present study was designed to determine the degree of immunological cross-reactivity between Sb-5 and eight other strains of S treptococcus bovis; and between LB-27 and four other isolates of Lactobacil lus. The cross-reactivity index (CRI, a low CRI indicates a high degree of immunological cross-reactivity) ranged from 7.3 to 56.1% between the strain s of S. bovis (the encapsulated strains with CRIs ranging from 7.3 to 12.4% ). For isolates of Lactobacillus the CRIs ranged from 11.5 to 72.2%. The re sults indicate that all the isolates tested have a certain degree of immuno logical homology with Sb-5 and LB-27, and suggest that the vaccine may cros s-react with a large number of strains of S. bovis and Lactobacillus which may cause lactic acidosis. As most of the S. bovis strains in the rumen are encapsulated, the high degree of homology between Sb-5 and encapsulated S. bovis strains further suggests that the vaccine containing Sb-5 may be eff ective against a wide range of strains of S. bovis in sheep and cattle. (C) 1999 Federation of European Microbiological Societies. Published by Elsevi er Science B.V. All rights reserved.