Photodynamic inactivation of Mycobacterium tuberculosis by broad-spectrum visible light.

Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis, a major infectious disease causing substantial global morbidity and mortality. The growing incidence of antibiotic-resistant strains highlights the urgency of identifying alternative strategies capable of targeting persistent and resistant forms of Mtb. This study evaluates the effectiveness of photodynamic inactivation (PDI) using visible light within the 400-420 nm range against a clinical Mtb isolate. The isolate was subjected to controlled LED exposure under biosafety level-3 conditions, with viability assessed via colony-forming unit counts. Results showed a significant reduction in Mtb viability, with > 99% (over 2-log) reduction observed after exposure to the tested visible light spectrum. These results provide a strong rationale for the clinical translation of visible light-based disinfection strategies, by indicating that visible light photoinactivation provides a practical, non-chemical alternative to conventional disinfectants and UV-based methods, reducing concerns about toxicity and operational limitations. This approach holds particular promise for healthcare environments, where it could contribute to reducing the environmental persistence of Mtb and, consequently, the risk of transmission. These results underscore the need for further investigation into light-based technologies as complementary tools to existing infection control measures, particularly in high-risk or inadequately sanitized settings. KEY POINTS: • Visible light (Soret Band 400-420 nm) significantly reduces Mycobacterium tuberculosis (Mtb) viability • No photosensitizers are used in the photodynamic inactivation (PDI) process  • LED-based visible light may help limit Mtb spread in clinical environments.