Inactivation of environmental mycobacteria by free chlorine and UV

The resistance of environmental mycobacteria (EM) against chlorine and ultraviolet (UV) was evaluated for determination of the Ct value and UV dose to inactivate EM. Chlorine disinfection experiments were done on Mycobacterium fortuitum in oxidant demand-free buffered water at the worst condition (pH 8.5, 4 degrees C) and normal condition (pH 7.0, 20 degrees C). The Ct value for 3log inactivation of M. fortuitum was 600 times greater than that of Escherichia coli. UV experiments were performed for various species of Mycobacterium avium, M. fortuitum, Mycobacterium intracellulare, and Mycobacterium lentiflavum. A UV collimated beam device was used for irradiation of four species suspended in phosphate buffered saline with doses of 5, 10, 20, 50, and 100mJ/cm(2). UV sensitivity of mycobacteria was species-specific. More than 3log of M. avium, M. intracellulare, and M. lentiflavum could be inactivated at 20mJ/cm(2), whereas M. fortuitum was so resistant that 3log inactivation required a dose of more than 50mJ/cm(2). Mycobacteria were found 2-10 times more resistant to UV than E. coli for 3log inactivation. There was no significant difference in the inactivation of mycobacteria with either low-pressure or medium-pressure UV irradiation.