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Lorena Zendejas Reyes, Andreina Tarff, Rebecca Yee, Marisol del Valle Cano, Laura Di Meglio, Praveena Gupta, William May, Arturo Casadevall, Ying Zhang, Ashley Behrens; Efficacy of high fluence ultraviolet light A (UVA) photoactivation of riboflavin in vitro as a therapy for keratitis. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3896. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Corneal cross-linking (CXL), the established modality to halt progressive corneal ectatic disorders represents a versatile approach for killing pathogens invading the cornea. It recent proposed modifications include protocols at higher UVA intervals. The purpose of our study was to determine the impact of a high UVA irradiance photo-activating B2 on bacterial viability.
Methicillin sensitive S. aureus (MSSA) Newman strain and methicillin resistant-multidrug resistant S. aureus (MDR-MRSA) USA300, CA409, CA127, GA656 and NY315 strains (107 CFU/ml) were exposed in 12-well culture plates to a UVA energy dose of 3.4-4 J (5.4-6 J/cm2) administered by two different irradiance regimens: A) 30 mW/cm2 for 3 min and B) 10 mW/cm2 for 10 min, at a wavelength of 365 nm through an 8-mm iris aperture in combination with B2 0.1% solution. B2 0.5% was used for Newman and CA409 strains. Control groups included: B2/UVA alone, CA409 strain exposed to B2 + UVA of 3 mW/cm2 for 30 min, and an untreated sample. The cell viability was assessed after 24 hours of incubation at 37 °C by cell forming unit (CFU) enumeration. Triplicate values were obtained. Mann-Whitney test was used for statistical analysis.
There was no statistical significance when comparing the log-difference CFU/ml-medians of the untreated samples with those of regimen A: Newman = 0.07, CA409 = 0.11, USA300 = 0.30, CA127 = 0.08, GA656 = 0.22, NY315 = 0.31 (p > 0.1). Likewise, no significance was observed between regimen B and the untreated sample: Newman = 0.10, CA409 = 0.12, USA300 = 0.22, CA127 = 0.16, GA656 = 0.22, NY315 = 0.35 (p > 0.1). B2 0.5% on Newman and CA409 strains exhibited no statistical significance for regimen A: Newman = 0.07, CA409 = 0.42 (p > 0.1), and regimen B: Newman = 0.29, CA409 = 0.20 (p > 0.1) compared with the untreated sample. The standard B2 0.1% + UVA (3mW/cm2 for 30 min) demonstrated 100% killing on strain CA409.
The photoactivation of B2 by a high UVA spectral density is not an effective method for bacterial killing. We acknowledge the significance of these results considering its null effectiveness in generating reactive oxygen species (ROS), which is also critical for corneal biomechanical stability.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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