In vitro Bactericidal Efficacy of Periowave Photodynamic Disinfection System

Purpose: To determine bactericidal efficacy of Periowave photodynamic disinfection (PDD) system using a small volume in vitro model.  Material and Methods:  Overnight cultures (25 µL) of E. coli (ATCC 11775) and E. faecalis (ATCC 4082) at approximately 10⁶/mL were delivered to wells of a 384-well microplate.  The light diffuser tip of Periowave PDD (Ondine Biopharma Corp., Vancouver, BC) immersed in the sample, with or without agitation, was illuminated for 1, 3 or 5 minutes.  The experiment was conducted in duplicate and repeated for two additional times, each with the PBS control, under minimal ambient lighting.  Immediately after the illumination treatment, a sample (20 µL) was withdrawn for spot plating onto a TSA plate.  In addition, another sample was taken for serial dilutions (10^-1, 10^-2, 10^-3, 10^-4, 10^-5) using the PBS.  Each dilution (20 µL) was spot plated in duplicates on TSA plates.  The plates were incubated for 24 hours at 37°C and then counted to determine the colony forming units (CFU/mL).  Results: The controls (PBS without light treatment) showed growth as expected.  The 1-minute treatment without agitation was insufficient to kill all E. faecalis and E. coli.  The 3-minute treatment without agitation for E. coli showed ³99% killing for the undiluted and 1:10 dilution compared to that for E. faecalis, which showed total killing of the organism.  The 5-minute treatment showed total killing for both organisms regardless of the agitation.  The combination of Periowave PDD system and agitation during treatment for 1-, 3- and 5-minute resulted in total killing of both organisms.  Conclusion: One-minute treatment of Periowave PDD system without agitation results in significant killing but not total eradication of E. faecalis or E. coli.  With agitation for ³1-minute the Periowave PDD system is capable of achieving total killing of both organisms. Sponsored by Ondine Biopharma Corp.