Relative immunogenicity of streptomycin-sensitive and -resistant strains of BCG.

Normal, specific pathogen-free mice were vaccinated intravenously with increasing amounts of a streptomycin-resistant variety of BCG Tice (BCG SM(R)). The behavior of BCG SM(R) in the lungs, liver, and spleen was followed quantitatively for up to 50 days. One or two intravenous doses of 10(6) viable organisms were steadily eliminated from the tissues without producing detectable tuberculin sensitivity or raising resistance to a subsequent challenge with Mycobacterium tuberculosis strain Erdman. But mice receiving six weekly injections of 10(6) viable BCG SM(R) or a single injection of 10(6) BCG SM(R) by the intravenous route did develop effective levels of antituberculous resistance. Heat inactivation of the BCG SM(R) inoculum removed the organism's protective activity which could, however, be restored by incorporation of the organisms into Freund adjuvant. The ability of living BCG SM(R) to induce an effective antituberculous resistance when introduced into the tissues in an appropriate manner is discussed in terms of the mechanism of antituberculous immunity.