The potential of visible blue light (405 nm) as a novel decontamination strategy for carbapenemase-producing enterobacteriaceae (CPE)

Background: Carbapenemase-producing Enterobacteriaceae (CPE) pose a considerable threat to modern medicine. New treatment options and methods to limit spread need to be investigated. Blue light (BL) is intrinsically antimicrobial, and we have previously demonstrated significant antimicrobial effects on biofilms of a panel of isolates, including two CPEs. This study was performed to assess the antibacterial activity of 405 nm BL against a panel of CPE isolates (four encoding bla _NDM , three bla _KPC , two bla _OXA-48 , and three encoding both NDM and OXA-48 carbapenemases). Methods: In vitro experiments were conducted on 72 h old biofilms of CPEs which were exposed to 60 mW/cm ² of BL. Changes to biofilm seeding were assessed by measuring the optical density of treated and untreated biofilms. Results: Twelve bacterial clinical isolates (comprising eight Klebsiella pnemoniae, one K. oxytoca, and three Escherichia coli) were tested. BL was delivered for 5, 15 and 30 min, achieving doses of 162, 54, and 108 J/cm ² , respectively. All of the CPEs were susceptible to BL treatment, with increasing reductions in seeding with increasing durations of exposure. At 30 min, reductions in biofilm seeding of ≥80% were observed for 11 of the 12 isolates, compared to five of 12 after 15 min. CPE-8180 was less susceptible than the rest, with a maximum reduction in seeding of 66% at 30 min. Conclusions: BL is effective at reducing the seeding of mature CPE biofilms in vitro, and offers great promise as a topical decontamination/treatment agent for both clinical and environmental applications.