Rose bengal photodynamic antimicrobial therapy to inhibit Pseudomonas aeruginosa keratitis isolates

To evaluate the in vitro efficacy of rose bengal and riboflavin photodynamic antimicrobial therapy for inhibition the growth of four Pseudomonas aeruginosa (P. aeruginosa) isolates. Four different clinical P. aeruginosa isolates were collected from patients with confirmed keratitis. Each strain was mixed with either sterile water, 0.1% riboflavin solution, or 0.1% rose bengal solution to yield a final bacteria concentration of 1.5 × 10⁷ CFU/mL. Aliquots from each suspension were plated onto nutrient agar in triplicate. Plates were separated into two groups: (1) no irradiation and (2) 5.4 J/cm² of radiant exposure with custom-made LED irradiation sources. Separate irradiation sources were used for each photosensitizer. The riboflavin groups used a UV-A light source (375 nm) and rose bengal groups used a green light source (525 nm). Plates were photographed at 72 h and custom software measured bacterial growth inhibition. Growth inhibition to riboflavin and rose bengal PDAT showed strain-dependent variability. All four strains of P. aeruginosa showed greatest growth inhibition (89–99%) in the green irradiated-rose bengal group. The UV-A-irradiated riboflavin showed inhibition of 24–44%. UV-A irradiation only showed minimal inhibition (7–14%). There was little inhibitory effect in the non-irradiated photosensitizer groups. Rose bengal PDAT had the greatest inhibitory effect on all four P. aeruginosa isolates. In the UV-A-irradiated riboflavin group, there was moderate inhibition within the irradiation zone; however, there was no inhibition in the non-irradiated groups. These results suggest that rose bengal PDAT may be an effective alternative treatment for Pseudomonas aeruginosa infections.