Bactericidal effect of ultraviolet C (UVC), direct and filtered through transparent plastic, on gram-positive cocci: an in vitro study.

The prevalence of wound infections caused by multidrug-resistant (MDR) bacteria is increasing along with concern about widespread use of antibiotics. In vitro studies have shown that ultraviolet radiation, especially UVC, is both an effective bactericidal and antifungal. However, evidence about its bactericidal effect on wounds covered with transparent dressings remains inconclusive. Transparent dressings are used to retain moisture over the wound as part of an intermittent negative pressure dressing-the Limited Access Dressing (LAD) technique. Because this dressing is designed to remain in place for a number of days, an in vitro study was conducted to explore the bactericidal effect of direct and indirect UVR through a transparent 0.15-mm thick transparent polythene sheet on Gram-positive cocci. Six bacterial strains were inoculated to sheep blood agar (SBA) plates and exposed to direct and filtered UVC (254 nm) for 5, 10, 15, 20, 25, and 30 seconds with one media serving as a control (no UVC exposure). Plates were subsequently incubated for 24 hours and bacterial growth observed. Each set of experiment was repeated three times. Direct UVC was shown to have good bactericidal effect (100% eradication of organisms inoculated) at durations ranging from a minimum of 5 seconds (methicillin-resistant, coagulase-negative Staphylococcus and Streptococcus pyogenes) to a maximum of 15 seconds (methicillin-susceptible Staphylococcus aureus and Enterococci species). No bactericidal effect was observed when UVC was filtered through a 0.15-mm thick transparent polythene sheet. The results confirm the bactericidal effect of UVC in vitro and suggest that this effect can be achieved after a very short period of time. At the same time, film dressings appear to filter UVC. This may help protect skin from exposure to UVC but also limits its utility for use with the LAD technique. In vivo studies to evaluate the shortest effective UVC treatment duration and follow-up clinical studies to ascertain treatment efficacy and effectiveness are needed.