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Quantitative antimicrobial efficacy of PACK-CXL for different bacterial strains as a function of UV fluence and irradiated volume

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Session Details

Session Title: Presented Poster Session: Cross-Linking

Venue: Poster Village: Pod 2

First Author: : S.Kling SWITZERLAND

Co Author(s): :    F. Hufschmied   E. Torres Netto   R. Zbinden   F. Hafezi              

Abstract Details


PACK-CXL (photoactivated chromophore for keratitis cross-linking) is currently used as an adjunct therapy to antibiotic medication in microbial infectious keratitis. This experimental study aimed at quantifying the efficacy of PACK-CXL as a function of three principal treatment parameters: UV fluence, bacterial strain and irradiated volume.


The study was conducted jointly at the Institute of Medical Microbiology at the University Hospital of Zurich (Switzerland) and the Ocular Cell Biology Laboratory, Center for Applied Biotechnology and Molecular Medicine at the University of Zurich (Switzerland).


Six distinct bacterial strains, including standardized strains and clinically isolated strains from keratitis patients, were analyzed. Bacterial concentrations between 102 and 108 cells/ml were used. Volumes of either 11μl (≈ 285μm-thick layer) or 40μl (≈ 1000μm-thick layer) were irradiated within a microtiter plate at different fluences (5.4 to 27 J/cm2) and irradiances (3, 9 and 18 mW/cm2). The bacterial killing rate (B†) was determined to evaluate the antimicrobial efficacy of PACK-CXL.


B† was similar (51±11%) in bacterial concentrations between 103 and 105 cells/ml. In 11 μl volume, SA-8352-4, bacillus subtilis, pseudomonas aeruginosa and ATCC-29213 (B†=52%) were most sensitive to PACK-CXL at 5.4 J/cm2, while a lactase-secreting clinical isolate (B†=19%) was least sensitive. When irradiating a larger volume (40 μl), all strains showed a trend to lower B† (on average by factor -2.4), which was significant in SA-8325-4 and ATCC-29213. In contrast, applying a higher UV fluence increased B†, from 50% at 5.4J/cm2 to 92% at 10.8J/cm2, to 100% at 16.2 J/cm2 and above.


Currently applied PACK-CXL treatment protocols do not achieve the maximal possible bacterial killing rate, and therefore should not be used as stand-alone treatment. The feasibility of applying UV fluences higher than 5.4 J/cm2 in a clinical setting requires further investigation.

Financial Disclosure:


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