High Fluence Increases the Antibacterial Efficacy of PACK Cross-Linking. Issue 8 (August 2020)

• Record Type: Journal Article
• Authors: Kling, Sabine; Hufschmid, Fong Siang; Torres-Netto, Emilio A.; Randleman, J. Bradley; Willcox, Mark; Zbinden, Reinhard; Hafezi, Farhad
• Is Part Of: Cornea. Volume 39:Issue 8(2020)
• Publication Date: 2020-08
• Subjects: PACK-CXL -- antibacterial efficacy -- UV fluence -- bacterial strain -- infectious keratitis; Cornea -- Periodicals; Cornea -- Periodicals; Cornée -- Périodiques; 617.719
• DOI: 10.1097/ICO.0000000000002335
• Languages: English
• ISSNs: 0277-3740

Abstract

Abstract : Purpose: Photoactivated chromophore for keratitis cross-linking (PACK-CXL) is used as an adjunct therapy to antibiotic medication in infectious keratitis. This experimental study aimed at quantifying the PACK-CXL efficacy as a function of UV fluence using several bacterial strains and irradiated volumes. Methods: Six distinct bacterial strains, including standardized strains and clinically isolated strains from patients with keratitis, were analyzed. Bacterial concentrations between 10 2 and 10 8 cells/mL were used (simulating small corneal ulcers). Volumes of either 11 μL (≈285 μm stromal thickness) or 40 μL (≈1000 μm stromal thickness) were irradiated within a microtiter plate at different fluences (5.4–27 J/cm 2 ) and irradiances (3, 9 and 18 mW/cm 2 ). The ratio of bacterial killing (B†) was determined to evaluate the antimicrobial efficacy of PACK-CXL. Results: B† was similar (51 ± 11%) in bacterial concentrations between 10 3 and 10 5 per ml. In 11 μL volume, Staphylococcus aureus (SA) 8325-4 ATCC 29213, Bacillus subtilis (BS) 212901, and Pseudomonas aeruginosa (PA) 2016-866624 were most sensitive to PACK-CXL at 5.4 J/cm 2 (on average B† = 49 ± 8%), whereas Klebsiella oxytoca (KO) 2016-86624 (B† = 25%) was least sensitive. When irradiating a larger volume, B† was on average lower in 40 μL (19 ± 18%), compared with 11 μL (45 ± 17%, P < 0.001). By contrast, applying a higher UV fluence increased B† of SA ATCC 29213, from 50% at 5.4 J/cm 2 to 92% at 10.8 J/cm 2, to 100% at 16.2 J/cm 2 and above. Conclusions: Applying higher UV fluences substantially increases the bacterial killing rates. Safety limits for clinical application require further investigation.