Chlorous Acid Inactivates <i>Mycobacterium Tuberculosis</i> with a Much Lower Available Chlorine Concentration than Sodium Hypochlorite

Mycobacterium tuberculosis is the causative agent of tuberculosis. Globally, it is one of the most significant bacteria in terms of responsibility for human mortality. To prevent the transmission of tuberculosis, it is essential to properly sterilize environments contaminated with Mycobacterium. For sterilization, sodium hypochlorite is commonly used to kill pathogens. However, M. tuberculosis usually shows high resistance to sodium hypochlorite. In this study, we compared the bactericidal activity of chlorous acid and sodium hypochlorite against M. tuberculosis in the presence or absence of artificial saliva. When 7.0 log CFU/mL of M. tuberculosis was treated with different concentrations of sodium hypochlorite or chlorous acid, it was found that, while 20,000 ppm of sodium hypochlorite was needed to reduce the pathogen below the detection limit, only 5 ppm of chlorous acid was required. Furthermore, when an experiment was performed in the presence of artificial saliva, 500 ppm of sodium hypochlorite was needed to reduce the M. tuberculosis below the detection limit, but only 25 ppm of chlorous acid was needed. That data indicates that chlorous acid is a more powerful disinfectant than sodium hypochlorite, regardless of the presence or absence of artificial saliva. Therefore, chlorous acid may be used as a useful bactericidal agent to sterilize clinical environments contaminated with M. tuberculosis.