The Effect of Radiation on Microbiologic Characteristics of M Tuberculosis

¹ Medical Services (Pulmonary Unit) and Radiology Department, Massachusetts General Hospital and Harvard Medical School, Boston, and Mattapan Chronic Disease Hospital, Mattapan, Mass
² Director of Laboratories, Mattapan Chronic Disease Hospital
³ Chief, Pulmonary Unit, Massachusetts General Hospital, Associate Professor of Medicine, Harvard Medical School

The effect of irradiation on mutation (expressing itself as drug resistance) and on viability of Mycobacterium tuberculosis was studied in vitro. Forty-two identical cultures of H37-Rv (M tuberculosis) were exposed to different levels of cobalt radiation (10, 100, 1,000, 2,500, 5,000, 10,000, and 20,000 rads) with six samples used for each of the seven radiation levels. Equivalent samples exposed to zero rads and samples handled and stored identically formed the controls. Coded cultures were read in a double-blind fashion to determine the number of surviving organisms and sensitivities to nine different antituberculosis drugs. Organism viability began to decrease at radiation levels of 1,000 rads and decreased linearly with higher levels of radiation. Three of the 42 radiated cultures developed drugrasistant organisms (one to INH, one to PAS, a third to SM). This drug resistance occurred at levels of clinical significance (> 1 percent control) as well as in amounts exceeding probability values for chance resistance mutation. High radiation levels such as occur in radiotherapeutic doses decrease the viability of M tuberculosis. Radiation may also induce genetic mutation expressed as primary drug resistance.