FACTORS AFFECTING VIRULENCE OF DRUG-RESISTANT BACTERIA

Animal Experiments with Isoniazid-Resistant Tubercle Bacilli

Abstract

1. After subcultures of isoniazid-susceptible tubercle bacilli on the media with isoniazid at various concentrations it was possible to isolate variants having low degree of resistance to the drug with and without attenuation of virulence. The latter was isolated by subcultures on the media containing isoniazid at low concentration, while the former was isolated by subcultures on the media containing isoniazid at relatively high concentrations.
2. When the virulent tubercle bacilli having low degree of resistance to isoniazid were subcultured on a media with isoniazid at moderate concentration, the variant having relatively high resistance to the drug was isolated without marked attenuation of virulence.
3. It was proposed that isoniazid concentration in the environment, in which tubercle bacilli grow, at the initiation of the isoniazid administration affects the virulence of isoniazid-resistant variants.