Effect of low dose of gamma radiation on multidrug resistant Mycobacterium tuberculosis

Multidrug resistance (MDR), defined as resistance to at least isoniazid (INH) and rifampin (RMP) which have the most effective bactericidal activity to M. tuberculosis, is now common throughout the world, with average rates of resistance of 15% in high-burden countries. Exposure of bacterial cells to low doses of ionizing radiation induces mutations that lead to genetic and subsequent phenotypic effects. Our aim was to study the effect of a low dose of gamma radiation, which is commonly used for treatment of most cancer patients, in altering the resistance of M. tuberculosis and analyze their effect on repairing gene mutations in the rpoB and KatG involving M. tuberculosis resistance to RMP and INH. M. tuberculosis strains resistant to RMP and INH were isolated, identified and exposed to 24.41Gy in-vitro gamma irradiation. The susceptibility tests to RMP and INH after irradiation were performed. Mutations in the rpoB and katG gene were analyzed by DNA sequencing of M. tuberculosis MDR clinical isolates before and after exposure to gamma radiation. The results revealed that after exposure 61.1% were sensitive to RMP and INH, 22.2% sensitive to RMP and resistant to INH while 16.7% remained MDR. As a result of comparing mutations of rpoB and katG gene before and after irradiation with respect to their mutations conferring RMP and INH resistance, a marked difference in the distribution of mutations was observed. Knowledge of the effect of radiation on M. tuberculosis would help to improve the treatment of tuberculosis. [Journal of American Science 2010;6(10):774‐780]. (ISSN: 1545‐1003).