Photoinactivation of Bacteria Attached to Glass and Acrylic Surfaces by 405 nm Light: Potential Application for Biofilm Decontamination

Attachment of bacteria to surfaces and subsequent biofilm formation remains a major cause of cross‐contamination capable of inducing both food‐related illness and nosocomial infections. Resistance to many current disinfection technologies means facilitating their removal is often difficult. The aim of this study was to investigate the efficacy of 405 nm light for inactivation of bacterial attached as biofilms to glass and acrylic. Escherichia coli biofilms (103–108 CFU mL−1) were generated on glass and acrylic surfaces and exposed for increasing times to 405 nm light (5–60 min) at ca 140 mW cm−2. Successful inactivation of biofilms has been demonstrated, with results highlighting complete/near‐complete inactivation (up to 5 log10 reduction on acrylic and 7 log10 on glass). Results also highlight that inactivation of bacterial biofilms could be achieved whether the biofilm was on the upper “directly exposed” surface or “indirectly exposed” underside surface. Statistically significant inactivation was also shown with a range of other microorganisms associated with biofilm formation (Staphylococcus aureus, Pseudomonas aeruginosa and Listeria monocytogenes). Results from this study have demonstrated significant inactivation of bacteria ranging from monolayers to densely populated biofilms using 405 nm light, highlighting that with further development this technology may have potential applications for biofilm decontamination in food and clinical settings. Microbial biofilms remain a major source of cross‐contamination in both food and clinical environments. This study investigates the efficacy of 405 nm light (ca 140 m Wcm−2) for biofilm decontamination. Successful inactivation of Escherichia coli biofilms (103–107 CFU mL−1) was demonstrated. Inactivation of Staphylococcus aureus, Pseudomonas aeruginosa and Listeria monocytogenes monolayer biofilms, and mixed‐species biofilms (S. aureus and E. coli) was also shown. Results highlight that indirect exposure to 405 nm light can successfully inactivate biofilms: antimicrobial activity is retained when transmitted through transparent materials [glass(left)/acrylic(right)]. With further development, this technology may have potential use for practical biofilm decontamination applications.