Efficacy of calcium hypochlorite and ultraviolet irradiation against Mycobacterium fortuitum and Mycobacterium marinum.

Abstract

Nontuberculous mycobacteria (NTM) cause opportunistic infections with increasing frequency in immunocompromised humans. Water is one of the natural sources for transmission of NTM and plays a major role in the epidemiology of NTM infections. This study evaluated the efficacy of calcium hypochlorite and ultraviolet irradiation (UV) to eliminate potentially zoonotic NTM species such as M. marinum and M. fortuitum. Bacterial suspensions containing1-4 × 105 CFU/ml were exposed to 5, 50, 100, 1,000 and 10,000 mg/L of Ca (OCl)2for 1, 5, 10, 15, 20, 30 and 60 minutes, and 6,000 μW/cm2 UV dose for 5, 10, 20, 30, 60 and 120 seconds. Of the two methods tested, UV irradiation was more effective than chlorine in achieving three log reduction in viable bacterial count (UV dose 6,000 μW/cm2, exposure time 60 S) as well as in eliminating the organisms (UV dose 17,000 μW/cm2, exposure time: 30 S). When 10,000 mg/L of chlorine was used, 10 and 20 min contact times were required to achieve three log inactivation and complete elimination of M. fortuitum respectively. Our study suggest that initial disinfection of water by chlorine at the water treatment plant followed by UV irradiation at the household level would minimise the spread of NTM to the susceptible population via drinking water.