Abstract
PurposeTo examine and compare the efficacy of in vitro growth inhibition using rose bengal and riboflavin photodynamic antimicrobial therapy (PDAT) for Nocardia keratitis isolates.Methods Nocardia asteroides complex, Nocardia amikacinitolerans, and Nocardia farcinica species were isolated from patients with confirmed Nocardia keratitis. Isolates were tested against three experimental groups: (1) no photosensitizer/no irradiation, (2) photosensitizer/no irradiation, and (3) photosensitizer/irradiation. Each isolate was prepared in suspension to a concentration of 1.5 × 108 CFU/mL. Bacterial suspensions were mixed with water or prepared 0.1% photosensitizer solution for a final bacterial concentration of 1.5 × 107 CFU/mL. Aliquots of 1 mL were plated on 5% sheep blood agar. Rose bengal and riboflavin PDAT plates were irradiated for 15 minutes with a 525- or 375-nm custom 6-mW/cm2 powered light source for a total fluence of 5.4 J/cm2. All experimental groups were repeated in triplicate. Plates were incubated in a 35°C non-CO2 incubator for 96 hours and photographed. Percent inhibition was evaluated using LabVIEW-based software.ResultsAll strains of Nocardia tested with 0.1% rose bengal and irradiated for 15 minutes demonstrated statistically significant inhibition of growth (P < 0.05). No other experimental groups displayed any bacterial inhibition.ConclusionsRose bengal is superior to riboflavin PDAT against selected Nocardia isolates. In vivo testing is warranted to investigate the utility of rose bengal PDAT for severe Nocardia keratitis.Translational RelevanceIn vitro results for three clinical strains of Nocardia support the possible use of rose bengal PDAT as a complementary treatment of Nocardia keratitis.
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