233 nm far-UV-C radiation for biofilm inactivation.

The formation of biofilms protects bacteria from antibiotic therapy or disinfection based on different mechanisms. The treatment of biofilms is furthermore impeded by their characteristic of being composed of multiple species; thus, it is necessary to identify involved species to determine an appropriate treatment. Consequently, new methods for inactivating involved bacteria in biofilms are necessary. One possibility might be the use of skin-compatible doses of 233 nm far-UV-C irradiation. In the presented study, the potential for biofilm formation of various bacteria species and strains was identified using a plate-based assay (crystal violet staining) as well as two cultivation-based assays on agar plates (Congo red, calcofluor). Strains of S. aureus, S. epidermidis, and P. aeruginosa were selected and grown on stainless steel carriers for 24 h followed by irradiation with skin-tolerable doses of 233 nm far-UV-C radiation (20-80 mJ/cm2). Viability of bacteria was assessed via quantification of colony-forming units. Irradiation led to a statistically significant inactivation of up to 2.28 lg (S. epidermidis), 2.60 lg (S. aureus), and 1.16 lg (P. aeruginosa). Higher doses tended to result in slightly higher inactivation, but without statistical significance. Since UV-C irradiation does not remove bacteria and the surrounding matrix, additional cleansing is necessary for biofilm removal. But UV-C irradiation can be an effective addition to cleansing and chemical treatment for biofilm inactivation. Therefore, for potential applications on skin or mucous membranes, UV-C currently represents a valuable additional method that broadens the antiseptic treatment repertoire.