Presence of Vi antigen in a virulent strain of leptospira interrogans serovar pomona and relation of Vi antigens of leptospiras to resistance to leptospiricidal activity mediated by antiserum plus complement.

Vi antigen was found in a virulent strain of Leptospira interrogans serovar pomona. The presence of Vi antigen was shown by the agglutinin-absorption and precipitin-absorption tests. Each strain of pomona and copenhageni which possessed Vi antigen and was resistant to the leptospiricidal activity mediated by the antiserum plus complement lost Vi antigen and became susceptible to the leptospiricidal activity when cultured in the presence of 8-azaguanine. The strains thus treated with 8-azaguanine recovered the resistance and Vi antigen when cultured in medium without 8-azaguanine.