Photodynamic Antimicrobial Therapy to inhibit Purpureocillium lilacinum, Pseudallescheria boydii and Cochliobolus lunatus isolates.

Abstract

Purpose : To assess the use of rose bengal- and riboflavin-mediated photodynamic antimicrobial therapy (PDAT) to inhibit the growth of three fungal isolates that cause infectious keratitis.

Methods : Three fungi, Purpureocillium lilacinum (Paecilomyces lilacinus), Pseudallescheria boydi, Cochliobolus lunatus (Curvularia lunata), were isolated from patients with confirmed fungal keratitis and grown on Sabouraud-Dextrose agar plates. Using the method we published previously (Arboleda et al, AJO 2014 Jul;158(1):64-70), triplicate test plates were separated into 7 groups: (1) control (fungal isolate only), (2) green irradiation only, (3) 0.1% rose bengal only, (4) 0.1% rose bengal-mediated PDAT (rose bengal + green irradiation), (5) UV irradiation only, (6) 0.1 % riboflavin only, and (7) 0.1% riboflavin-mediated PDAT (riboflavin + UV-A irradiation). Irradiation was performed using either a 47mm diameter 518nm green light emitting diode (LED) array or a 37mm diameter 375nm UV-A LED array for a final energy density of 5.4 J/cm². After treatment, plates were placed in a 30°C non-CO₂incubator and observed for growth. Plates were photographed at day 3 to document fungal growth and images were analyzed using a Labview program created in our laboratory.

Results : Rose bengal-mediated PDAT successfully inhibited the growth of Purpureocilium lilacinum and Pseudallescheria boydii. For these two fungi, rose bengal-mediated PDAT showed complete inhibition within the central 47mm area corresponding to the diameter of the light source at day 3. Cochliobolus lunatus showed minimal inhibition in the central region, but no clear inhibition zone. No other groups demonstrated any inhibitory effect on the three fungal isolates.

Conclusions : Rose bengal-mediated PDAT inhibited Purpureocilium lilacinum and Pseudallescheria boydii keratitis isolates within the irradiated area; however it was not effective for Cochliobolus lunatus. Rose bengal-mediated PDAT has the potential to be a treatment option for fungal keratitis.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

 

Inhibition of three fungal species: (Row 1) Control, (Row 2) Green Irradiation Only, (Row 3) 0.1% Rose Bengal Only, (Row 4) 0.1% Rose bengal-mediated PDAT.

 

Inhibition of three fungal species: (Row 1) Control, (Row 2) UV-A Irradiation Only, (Row 3) 0.1% Riboflavin Only, (Row 4) 0.1% Riboflavin-mediated PDAT.