Virulence for guinea pigs of tubercle bacilli isolated from the sputum of participants in the BCG trial, Chingleput District, South India.

This study, conducted in Madras, India and in Madison, Wisconsin, USA, was concerned with the virulence of isolates of Mycobacterium tuberculosis obtained from the sputum of individuals living in the Chingleput district of south India. The following results were obtained. 1. The findings of Mitchison with respect to the predominance of low virulence for guinea pigs among isolates from persons living Madras, were confirmed on isolates from the sputum of residents of the Chingleput district. 2. A high correlation was found between the log10 number of tubercle bacilli recovered from the spleen of guinea pigs infected intramuscularly with 1.0 mg of tubercle bacilli and the root index of virulence. 3. A high correlation was found between the log10 number of tubercle bacilli recovered from the spleen of guinea pigs infected intramuscularly with 1.0 mg of tubercle bacilli and the number recovered from the spleen of guinea pigs infected by the respiratory route with 5-10 tubercle bacilli. 4. Relatively low correlations were found between RIV and the susceptibility of isolates to thiophene-2 carboxylic acid hydrazide or to hydrogen peroxide.