STUDIES IN THE VARIABILITY OF TUBERCLE BACILLI.: VIII. BCG.

Abstract

Five cultures of BCG have been shown to consist primarily or entirely of R type tubercle bacilli and to resemble R types from other sources. When received one culture contained a few S types which were isolated. The other four cultures appeared to consist entirely of R types. After a long series of cultures, particularly in slightly alkaline Proskauer and Beck's fluid, dissociation occurred and S types were isolated from two strains; no stable S types could be recovered from two additional strains.The R, or ordinary BCG produced only localized infections, the S forms produced fatal progressive tuberculosis in guinea pigs. The degree of tissue involvement in fatal cases was generally less than with typical virulent tubercle bacilli.By means of complement fixation reactions it was shown that the S form recovered from BCG cultures, like typical S virulent mammalian tubercle bacilli, contains a specific antigenic substance which is lacking in the ordinary BCG and other R forms of the species. Animals immunized with S organisms are shown to develop a specific S antibody which is not present in the serum of animals treated with R organisms or the ordinary form of BCG. It is suggested that this lack of antigenic substance in the BCG militates against its effectiveness as an immunizing agent.