Prevention of photo-repair recovery following pulsed UV-light treatment of straphylococcus aureus: implications for decontamination applications

Pulsed UV-rich (PUV) light is a sterilisation technology which utilises high peak power applied over short time periods, resulting in rapid microbial inactivation. It inactivates microorganisms through the generation of DNA mutations which prevent bacterial replication, rendering cells inactive. Many bacteria, however, possess DNA repair mechanisms, the most notable being photoreactivation, which utilises 300-500 nm wavelength light to repair UVinduced damage.
The present study examines the photoinactivation and photoreactivation capability of Staphylococcus aureus, an important bacterial pathogen. A xenon flashlamp was used for inactivation of suspensions of varying population density, with fewer than 10 pulses of UV-rich light required to achieve a 7-log10 reduction in population. Photoreactivation of sub-lethally damaged cells was investigated and exposure to 370 nm light was found to induce up to a 3-log10 increase in viable cell count, with this maximum decreasing upon increasing pulsed UV-rich light damage.
The use of PUV-light is effective for inactivation of bacteria, however elucidation of the lethal doses required for complete inactivation is necessary to prevent the possibility of subsequent photoreactivation of sub-lethally damaged cells, which could compromise the use of this technology in medical and commercial decontamination applications.