The Relation of Oxygen Tension to Virulence of Tubercle Bacilli and to Acquired Resistance in Tuberculosis

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Abstract
The rate of multiplication in the lungs of mice of the so-called "avirulent", "attenuated" and virulent strains of tubercle bacilli can be altered by changes in the oxygen tension of the environment in which the animals are maintained. Under the influence of a high oxygen level (60 volumes percent) increased multiplication of the H37Ra and BCG strains occurred; and the virulence of the H37Rv strain of Mycobacterium tuberculosis for mice probably was increased. In view of this it was suggested that the H37Ra strain should be classified as an "attenuated" strain. A low oxygen level (10 volumes percent) increased markedly the survival of mice injected with the H37Rv strain. A high oxygen level (60 volumes percent) significantly prolonged the survival of BCG immunized mice challenged with the virulent H37Rv strain of M. tuberculosis. This prolongation of survival may have been related to the partial alleviation of the pulmonary insufficiency which is known to occur in these animals. Acquired resistance to tuberculosis may be due, at least in part, to the rapid migration of macrophages into tuberculous areas which would result in local anoxia of a degree sufficient to inhibit multiplication of tubercle bacilli.