Bacteria and RNA virus inactivation with a high-irradiance UV-A source

Area of Science:

• Microbiology
• Photochemistry
• Environmental Science

Background:

• Ultraviolet (UV) disinfection using mercury lamps is being replaced by eco-friendly LED alternatives.
• UV-A disinfection efficacy depends on pathogen type and requires optimized time/dose relationships.
• Pathogen inactivation by UV-A involves reactive oxygen species (ROS) and direct nucleic acid damage.

Purpose of the Study:

• To evaluate the disinfection efficacy of a 10 W UV-A LED (365-375 nm) against bacteria and viruses.
• To establish the time/dose relationship for UV-A inactivation of specific pathogens.
• To explore the mechanisms of UV-A inactivation, including ROS production and direct RNA damage.

Main Methods:

• UV-A inactivation assays were performed on Escherichia coli (E. coli), MS2 bacteriophage, and Semliki Forest virus (SFV).
• High irradiance (approx. 0.46 W/cm²) UV-A LED was used for disinfection experiments.
• ROS production was measured in irradiated E. coli, and viral gene expression was assessed after RNA irradiation.

Main Results:

• The 4-log10 reduction doses for E. coli and SFV were 268 J/cm² and 241 J/cm², respectively.
• A 2.5-log10 reduction of MS2 bacteriophage required 679 J/cm² over 30 minutes, demonstrating significant inactivation of non-enveloped viruses.
• ROS production correlated with E. coli inactivation, and direct UV-A damage to viral RNA reduced gene expression.

Conclusions:

• High-irradiance UV-A LED disinfection is effective against bacteria and enveloped viruses.
• UV-A demonstrates significant potential for inactivating UV-A-resistant non-enveloped viruses.
• Direct damage to viral RNA is a key mechanism in high-irradiance UV-A LED-mediated virus inactivation.