Some Studies on Three Strains of Streptococcus bovis Isolated from Cattle and Sheep after Overfeeding with Wheat

Three strains of streptococcus bovis were isolated from the ruminal contents of sheep and cattle: SbS45 from a sheep; Sb-Cl8 and Sb-CS from different steers. All the strains were found in large number(more than lo* per ml) in the rumen fluid samples after the animals were overfed with wheat and the acute lactic acidosis occurred, but the strains presented only in small numbers ranging from lo4 to 1 OS per ml before the animals being challenged with grain diets. Antibiotic resistance analysis indicated that the MIC (minimum inhibition concentration) of virginiamycin to Sb-CS was about 40 @ml irt vitro, but the other two strains were much more sensitive to this antibiotic(table). This test was conducted by adding virginiamycin into the culture broth and making into different final concentrations, and then observed the growth of the strains in the virginiamycin containing broths. Some differences of substrate fermentation in the strains were also detected (Table 1). ELISA analysis showed that Sb-CS had less ability to bind with the antibody in the standard serum by coating the plates with the three strains( 1 O8 cells/ ml),separately. The serum was obtained from the animals vaccinated by anti-S. bovis vaccine. When the antibody unit was 1 OO(Serum dilution: 1:8000), the OD was 1.415 for Sb-C5, while the OD value was higher than 2.255 for the other two strains(Figure 1). These results suggested that the antigenic property of Sb-C5 is markedly different from those of the other two strains.