Inactivated Saccharomyces cerevisiae as virulence-enhancing agent in the toxicity test of Salmonella typhi and the immunity assay of typhoid vaccine in mice.

Mucin has been used as virulence-enhancing (VE) agent in estimation of the toxicity of bacteria to mice and the potency of bacterial vaccines such as typhoid vaccine. Discontinuance of the acceptable brand of mucin made it necessary to search for an effective alternative. Five percent inactivated Saccharomyces cerevisiae (IY) showed a significant higher VE effect on S. typhi in mice (132 colony forming units/LD50) with lower viscosity when compared to 5% mucin (740 colony forming units/LD50), and either one could promote bacterial lethal toxicity in mice more than 10(4) times. The strong correlation (r2 = 0.9765) between the immune dose and the ratio of mouse death was found by using 5% IY as VE agent in the active mouse protection test for typhoid vaccine. The relative potencies of a typhoid vaccine to the reference vaccine obtained by using 5% mucin or 5% IY as VE agent were not significant difference. Therefore, IY was a suitable substitute for mucin as a VE agent in the toxicity test of bacteria and in the immunity assay of typhoid vaccines.