In vitro anti-biofilm efficacy of therapeutic low dose 265 nm UVC.

PURPOSE: Preclinical studies have confirmed the safety and efficacy of narrowband low-intensity ultraviolet C light (UVC) in managing bacterial corneal infection. To further consolidate these findings, the present study aimed to explore in vitro anti-biofilm efficacy of low-intensity UVC light for its potential use in biofilm-related infections.

METHODS

Pseudomonas aeruginosa biofilm was grown in chamber well slides for 48 h and exposed to one of the following challenges: UVC (265 nm wavelength, intensity 1.93 mW/cm2) for 15 s, 30 s, 60 s or 120 s duration, 70% propanol (positive control), or no exposure (negative control). Bacterial LIVE/DEAD staining was conducted at 1 h, 4 h, 6 h and 8 h after challenge exposures to assess the temporal pattern of biofilm inactivation, and slides were imaged using confocal microscopy. Treatment efficacy was quantified by dead biofilm biomass (volume/area - μm3/μm2) for different treatment groups at each time point.

RESULTS

At each time point post-exposure, dead biofilm biomass was consistently higher in the alcohol- and UVC-challenged groups than in the unchallenged control (p < 0.05), suggesting a sustained biocidal impact after a given challenge. The quantity of dead biofilm biomass did not differ between UVC groups at any time point (p > 0.05). Observed by confocal microscopy, UVC-exposed biofilm demonstrated predominantly intermediate-stage biofilm (i.e., dying state) at 1 h, which progressed to dead biofilm by 4 h.

CONCLUSION

Low doses of UVC demonstrated potent anti-biofilm activity, even in exposures as short as 15 s, the dose that has previously been deemed to be effective in managing corneal infection in vivo. These data support the potential for this UVC light-based technology to serve as an affordable, convenient, and effective means of treating ocular infections associated with bacterial biofilm.