Effect of 0.1% Fluorescein dye on Riboflavin Photodynamic Antimicrobial Therapy for inhibition of Methicillin-Resistant Staphylococcus aureus.

Abstract

Purpose : Controversy exists regarding the use of fluorescein prior to riboflavin mediated photodynamic antimicrobial therapy (PDAT). Some researchers report that fluorescein used to stain corneal epithelium, competes with riboflavin for the absorption of UV-A and thus reduces the antimicrobial effect of the PDAT procedure. The hypothesis that fluorescein dye has an inhibitory effect on the riboflavin mediated PDAT was evaluated in the current study.

Methods : MRSA strains were isolated from the corneal scraping of patients with confirmed bacterial keratitis. The MRSA isolates were mixed with appropriate photosensitizing solutions (0.1% riboflavin or 0.1% fluorescein or 0.1% riboflavin with 0.1% fluorescein) and plated on blood agar plates which were then exposed to PDAT (UV-A radiation exposure for 15-minutes). The custom-built UV-A light source 365 nm LED provided total energy of 5.4J/cm² (Dresden protocol). After the light exposure, all plates were placed in an incubator at 30°C and were photographed after 48 hours.

Results : Four strains of MRSA (2 healthcare-associated and 2 community-associated) were used for the in-vitro experiments. The control agar plates (Fig 1A) showed growth of MRSA isolates indicating the presence of viable organisms. Among the agar plates exposed to UV-A light: i) 0.1% riboflavin (Fig 1B), ii) 0.1% fluorescein (Fig 1C) and, iii) 0.1% fluorescein + 0.1% riboflavin (Fig 1D), there was no difference in the growth pattern of MRSA isolates. MRSA isolates grew all over the agar plates irrespective of the use of 0.1% fluorescein dye.

Conclusions : The current study showed that the riboflavin-mediated PDAT has no beneficial effect for the inhibition of MRSA strains. Also, use of 0.1% fluorescein dye did not affect the efficacy of riboflavin-mediated PDAT.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

 

Figure 1. Agar culture plates with 4 MRSA strains. Control group (A) and groups with 15 minutes of UV-A light exposure (B), (C) & (D) show growth of MRSA all over the plates irrespective of the use of fluorescein or riboflavin. The area within the small blue circles indicate the area of light exposure during PDAT.
(Abbreviations - PDAT- photodynamic antimicrobial therapy, MRSA- Methicillin-resistant Staphylococcus aureus, HA- healthcare-associated MRSA, CA-community-associated MRSA)