The consistency of the virulence in the Guinea-Pig of Tubercle Bacilli isolated on difference occasions from South Indian Patients before treatment

Isoniazid- and streptomycin-sensitive cultures of tubercle bacilli, isolated pretreatment from 12 South Indian patients when they first attended the Centre, and at 7 and 42 days thereafter, were tested for their virulence in the guinea-pig. The variation in virulence between patients was greater than the variation between cultures from the same patient. Thus, consistent differences exist between the virulence of strains of tubercle bacilli isolated from different Indian patients. No systematic alteration in virulence occurred during the 42-day period, during which no patient was receiving anti-tuberculosis chemotherapy. The variation in virulence between cultures obtained from the same patient was no greater than could be attributed to natural variation in the response of the guinea-pigs