Bactericidal Efficacy of High Irradiance Ultraviolet A Photoactivation of Riboflavin Versus Standard Corneal Cross-Linking Protocol In Vitro

Purpose: The purpose of this study was to compare the efficacy of high ultraviolet A (UVA) irradiance photoactivation of riboflavin (vitamin B2) versus the standard corneal cross-linking protocol on bacterial viability. Methods: Methicillin-sensitive Staphylococcus aureus (MSSA) Newman strain and methicillin-resistant multidrug-resistant S. aureus (MDR-MRSA) USA300, CA409, CA127, GA656, and NY315 strains were exposed to a UVA energy dose of 5.4 to 6 J/cm(2) by 2 high irradiance regimens: A) 30 mW/cm(2) for 3 minutes and B) 10 mW/cm(2) for 10 minutes with B2 0.1%. Control groups included B2/UVA alone, CA409 exposed to standard B2 0.1% + UVA (3 mW/cm(2) for 30 minutes), and an untreated sample. Cell viability was assessed. Triplicate values were obtained. The Mann-Whitney test and Student t test were used for statistical analysis. Results: There was no difference comparing the median bacterial load (log CFU/mL) of the untreated samples versus regimen A: Newman P = 0.7, CA409 P = 0.3, USA300 P = 0.5, CA127 P = 0.6, GA656 P = 0.1, and NY315 P = 0.2 (P >= 0.1); and B: Newman P= 0.1, CA409 P = 0.3, USA300 P = 0.4, CA127 P = 0.6, GA656 P = 0.1, and NY315 P = 0.3 (P >= 0.1). Standard regimen killed 100% of CA409. Conclusions: Photoactivation of B2 by high UVA irradiance does not seem to be effective for bacterial eradication in this study.

Automated summary

This study compares the efficacy of high UVA irradiance photoactivation of riboflavin with the standard corneal cross-linking protocol on bacterial viability. The results show that high UVA irradiance photoactivation does not seem to be effective for bacterial eradication.