Stability of Vi Antigen of Salmonella typhi. ∗

The lability of the Vi antigen of the typhoid bacillus has been emphasized as its most marked characteristic. Felix and Pitt 1 , 2 found that Vi antigen was destroyed in 90 minutes at 58°C and in an hour at 100°C and disappeared when treated with alcohol, chloroform or toluol. Exposure to ether resulted in a partial loss of the substance. Kauffmann 3 suggested the use of formalized suspensions for agglutination tests. Felix and Bhatnagar 4 reported that formalized suspensions retained their agglutinability by Vi antiserum and their agglutinogenic properties. Serums prepared with formalized suspensions were, however, inferior in protective antibodies to serums prepared with living organisms. They also found that phenolized suspensions progressively lost their agglutinability by Vi antiserum and serums produced with such suspensions contained no Vi agglutinins and were devoid of protective antibodies. Felix and Pitt 5 found that alcohol-treated suspensions retained their agglutinogenic and agglutinin-binding properties but that their agglutinability by Vi serums was “almost annulled or at least very much reduced.” Felix and Petrie 6 also stated that alcohol treatment almost annulled the Vi agglutinability. All the workers cited above observed that as the agglutinability of the bacilli by Vi antiserums disappeared they progressively became more agglutinate by O antiserums.

Since the observations of the writer were not in full accord with the descriptions of the characteristics of Vi antigen, particularly as regards its susceptibility to heat and alcohol, a systematic study of influence of temperature and certain chemicals on the substance was undertaken. The Watson strain of S. typhi was used because of the constancy of its content of Vi antigen. Additional experiments with other strains of S. typhi gave comparable results.