An investigation into the light inactivation of medically important microorganisms
Infection control is an area of increasing interest due to the failure of traditional disinfection and sterilisation methods, and of course, the significant problems associated with microbial multiple-antibiotic resistance. This study investigated light-based methods for the inactivation of a range of medically important bacteria. Initial investigations involved the design and development of a PUV-light airdisinfection system for the control and prevention of airborne infection. This system was tested in-situ for its efficiency to decontaminate air in university lecture theatres. Results demonstrated an 80% reduction in the level of airborne bacterial population, with the majority of the surviving isolates being saprophytic, pigmented Micrococcus spp. which pose no risk to human health. The second, and most significant, area of this study was the discovery, development and application of a visible-light treatment for the inactivation of MRSA and other medically important Gram-positive bacteria including Clostridium, coagulasenegative Staphylococcus, Streptococcus and Enterococcus species. The lethality of blue-light, and white-light containing blue-light, for these organIsms was demonstrated through a series of filter studies, and identification of the causative wavelengths to within a 10 nm bandwidth allowed the selection of a more efficient high-intensity narrow-band light source, now termed HlNS-light. Based on experimental data obtained from this study, it is proposed that Staphylococcus inactivation by blue light is brought about through singlet oxygen e02) generation by the photo-excitation of naturally-occurring endogenous porphyrins within the bacteria. This process has not previously been documented as a possible inactivation pathway for Staphylococcus aureus. Although not as germicidally efficient as UV-light, this HlNS-light system has the great advantage of being non-detrimental to human health, thus posing no problems with continuous exposure in occupied rooms, such as hospital wards. Consequently, HINS-light may prove to be an effective, non-harmful method for the control and prevention of MRSA transmission within the health-care environment.