Disinfection and damage of nontuberculous mycobacteria by different UV wavelengths

Nontuberculous mycobacteria (NTM) infection is a rising global concern and a severe opportunistic waterborne infectious disease. NTM has frequently been found in municipally treated water. Distinct colony morphotypes of NTM have different cell structure properties and, therefore, different resistance to disinfectants, which has given rise to the need to further explore mechanisms that underlie mycobacterial damage by ultraviolet (UV) radiation. Several studies have investigated NTM response to 254 nm UV, but their reaction to 222 nm is largely unknown. This study investigated the treatment efficiency of different UV wavelengths (222 nm emitted by a KrCl excimer lamp and 254 nm emitted by a low-pressure Hg lamp) on inactivating non-pathogenic NTM ( Mycobacterium smegmatis ) and clinically relevant Mycobacterium intracellulare , and damaging rpoB and hsp65 genes in smooth and rough morphotypes of these two NTM species. Results indicated that non-clinically relevant M. smegmatis grows faster than clinically relevant M. intracellulare and is less resistant to both UV wavelengths. Cell structure was found to play an important role in the resistance of NTM to UV, where rough morphotypes without glycopeptide lipids were more resistant. Gene damage analyzed by quantification of rpoB and hsp65 genes indicated that 222 nm caused slightly more gene damage than 254 nm, and smooth morphotypes exhibited higher gene damage than rough morphotypes. Exploring UV mechanisms across different NTM species, morphotypes, and their genes will enhance monitoring and control of NTM in water systems, as well as targeting UV development toward specific pathogens to minimize health threats posed by NTM.

IMPORTANCE

Nontuberculous mycobacteria (NTM) are found naturally in the environment and in treated water. NTM can cause opportunistic pathogen infections, which are a growing waterborne public health burden. Disinfection by ultraviolet (UV) light is a possible solution. Here, we showed that cell colony morphotype contributed to UV disinfection resistance, where rough morphotypes without glycopeptide lipids were more resistant to both disinfection and gene damage by both wavelengths we studied. Among wavelengths, 222 nm caused slightly more gene damage than 254 nm. Understanding the response of different NTM cell types and components to different wavelengths of UV light will inform the design and optimization of effective and efficient water treatment systems.