Public Health Significance of Tubercle Bacilli Resistant to Isoniazid

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Abstract
Guinea pigs and mice were injected with mixtures of isoniazid-resistant and isoniazid-sensitive tubercle bacilli. The inocula consisted of 100% sensitive organisms; 50% sensitive and 50% resistant; 90% resistant and 10% sensitive; 98% resistant and 2% sensitive. After autopsy of animals, lesions were cultured and tubercle bacilli tested for isoniazid sensitivity. Guinea pigs were injected with sensitive strains of tubercle bacilli; 25 days later (7 days after becoming tuberculin-positive) they were reinjected with isoniazid-resistant tubercle bacilli. After autopsy the tubercle bacilli isolated were tested for sensitivity to isoniazid. The results indicate that resistant tubercle bacilli play little, if any part, in formation of tubercles in guinea pigs or mice under conditions of the experiments described. Possible significance of isoniazid-resistant organisms is discussed.