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. 2023 Feb 1;12(2):12.
doi: 10.1167/tvst.12.2.12.

The Antibacterial Efficacy of High-Fluence PACK Cross-Linking Can Be Accelerated

Nan-Ji Lu  1   2   3 , Hendrik Koliwer-Brandl  4 , Francesca Gilardoni  3 , Nikki Hafezi  2   3 , Boris Knyazer  5 , Asaf Achiron  6 , Reinhard Zbinden  4 , Adrian Egli  4 , Farhad Hafezi  1   3   7   8   9
Affiliations

The Antibacterial Efficacy of High-Fluence PACK Cross-Linking Can Be Accelerated

Nan-Ji Lu et al. Transl Vis Sci Technol. .

Abstract

Purpose: To determine whether high-fluence photoactivated chromophore for keratitis cross-linking (PACK-CXL) can be accelerated.

Methods: Solutions of Staphylococcus aureus and Pseudomonas aeruginosa with 0.1% riboflavin were prepared and exposed to 365 nm ultraviolet (UV)-A irradiation of intensities and fluences from 9 to 30 mW/cm2 and from 5.4 to 15.0 J/cm2, respectively, representing nine different accelerated PACK-CXL protocols. Irradiated solutions and unirradiated controls were diluted, plated, and inoculated on agar plates so that the bacterial killing ratios (BKR) could be calculated. Additionally, strains of Achromobacter xylosoxidans, Staphylococcus epidermidis, and Stenotrophomonas maltophilia were exposed to a single accelerated PACK-CXL protocol (intensity: 30 mW/cm2, total fluence: 15.0 J/cm2).

Results: With total fluences of 5.4, 10.0, and 15.0 J/cm2, the range of mean BKR for S. aureus was 45.78% to 50.91%, 84.13% to 88.16%, and 97.50% to 99.90%, respectively; the mean BKR for P. aeruginosa was 69.09% to 70.86%, 75.37% to 77.93%, and 82.27% to 91.44%, respectively. The mean BKR was 41.97% for A. xylosoxidans, 65.38% for S. epidermidis, and 78.04% for S. maltophilia for the accelerated PACK-CXL protocol (30 mW/cm2, 15 J/cm2).

Conclusions: The BKR of high-fluence PACK-CXL protocols can be accelerated while maintaining a high, but species-dependent, BKR. The Bunsen to Roscoe law is respected in fluences up to 10 J/cm2 in S. aureus and P. aeruginosa, whereas fluences above 10 J/cm2 show strain dependence.

Translational relevance: The high-fluence PACK-CXL protocols can be accelerated in clinical practice while maintaining high levels of BKR.

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Conflict of interest statement

Disclosure: N.-J. Lu, None; H. Koliwer-Brandl, None; F. Gilardoni, None; N. Hafezi, None; B. Knyazer, None; A. Achiron, None; R. Zbinden, None; A. Egli, None; F. Hafezi, chief scientific officer of EMAGine AG (Zug, Switzerland) (E); co-inventor of the PCT applications CH2012/0000090 and PCT2014/CH000075 regarding CXL technology (P)

Figures

Figure 1.
Figure 1.
The BKRs of S. aureus (a, b, c) and P. aeruginosa (d, e, f) under the same total fluence of 5.4 J/cm2 (protocols 1–3), 10.0 J/cm2 (protocols 4–6), and 15.0 J/cm2 (protocols 7–9) with different irradiation intensity.
Figure 2.
Figure 2.
The BKRs of S. aureus (a) and P. aeruginosa (b) under the same irradiation intensity (30 mW/cm2) with three different total fluences (protocol 3, protocol 6, and protocol 9).
See this image and copyright information in PMC

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