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. 2020 Apr 10;9(4):171.
doi: 10.3390/antibiotics9040171.

Visible Light as an Antimicrobial Strategy for Inactivation of Pseudomonas fluorescens and Staphylococcus epidermidis Biofilms

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Visible Light as an Antimicrobial Strategy for Inactivation of Pseudomonas fluorescens and Staphylococcus epidermidis Biofilms

Valeria Angarano et al. Antibiotics (Basel). .

Abstract

The increase of antimicrobial resistance is challenging the scientific community to find solutions to eradicate bacteria, specifically biofilms. Light-Emitting Diodes (LED) represent an alternative way to tackle this problem in the presence of endogenous or exogenous photosensitizers. This work adds to a growing body of research on photodynamic inactivation using visible light against biofilms. Violet (400 nm), blue (420 nm), green (570 nm), yellow (584 nm) and red (698 nm) LEDs were used against Pseudomonas fluorescens and Staphylococcus epidermidis. Biofilms, grown on a polystyrene surface, were irradiated for 4 h. Different irradiance levels were investigated (2.5%, 25%, 50% and 100% of the maximum irradiance). Surviving cells were quantified and the inactivation kinetic parameters were estimated. Violet light could successfully inactivate P. fluorescens and S. epidermidis (up to 6.80 and 3.69 log10 reduction, respectively), while blue light was effective only against P. fluorescens (100% of maximum irradiance). Green, yellow and red irradiation neither increased nor reduced the biofilm cell density. This is the first research to test five different wavelengths (each with three intensities) in the visible spectrum against Gram-positive and Gram-negative biofilms. It provides a detailed study of the potential of visible light against biofilms of a different Gram-nature.

Keywords: Biofilm; Pseudomonas fluorescens; Staphylococcus epidermidis; antimicrobial inactivation; disinfection; inactivation kinetics; light-emitting diode; photodynamic inactivation; polystyrene surface; visible light.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Inactivation and sublethal injury kinetics of P. fluorescens. Inactivation kinetics (first column) and sublethal injury (SI) kinetics (second column) for P. fluorescens biofilms following irradiation with (a) violet, (b) blue, (c) green, (d) yellow and (e) red LED arrays. Inactivation kinetics: the black symbols (o for general medium,GM, and x for selective medium, SM) and lines (solid line for GM, dashed line for SM) represent the control (no light exposure). Likewise, the colored symbols and lines represent the fitting after 2.5% (only for violet LED array, light blue), 25% (yellow), 75% (green) and 100% of Imax (red). Sublethal injury kinetics: the colored lines represent the SI after 2.5% (only for violet LED array, light blue), 25% (yellow), 75% (green) and 100% of Imax (red).
Figure 2
Figure 2
Inactivation and sublethal injury kinetics of S. epidermidis. Inactivation kinetics (first column) and sublethal injury (SI) kinetics (second column) for S. epidermidis biofilms following irradiation with (a) violet, (b) blue, (c) green, (d) yellow and (e) red LED arrays. Inactivation kinetics: the black symbols (o for GM, x for SM) and lines (solid line for GM, dashed line for SM) represent the control (no light exposure). Likewise, the colored symbols and lines represent the fitting after 2.5% (only for violet LED array, light blue), 25% (yellow), 75% (green) and 100% of Imax (red). Sublethal injury kinetics: the colored lines represent the SI after 2.5% (only for violet LED array, light blue), 25% (yellow), 75% (green) and 100% of Imax (red).
Figure 2
Figure 2
Inactivation and sublethal injury kinetics of S. epidermidis. Inactivation kinetics (first column) and sublethal injury (SI) kinetics (second column) for S. epidermidis biofilms following irradiation with (a) violet, (b) blue, (c) green, (d) yellow and (e) red LED arrays. Inactivation kinetics: the black symbols (o for GM, x for SM) and lines (solid line for GM, dashed line for SM) represent the control (no light exposure). Likewise, the colored symbols and lines represent the fitting after 2.5% (only for violet LED array, light blue), 25% (yellow), 75% (green) and 100% of Imax (red). Sublethal injury kinetics: the colored lines represent the SI after 2.5% (only for violet LED array, light blue), 25% (yellow), 75% (green) and 100% of Imax (red).
Figure 3
Figure 3
Violet LED treatments. Inactivation by light of P. fluorescens (round symbols) and S. epidermidis (squared symbols) under violet exposure with 2.5%, 25%, 75% and 100% of Imax. The * symbol indicates significant differences (p < 0.05).
Figure 4
Figure 4
Dose for 1-log reduction. Dose for 1-log10 reduction as a function of the irradiance. P. fluorescens (round symbols) and S. epidermidis (squared symbols) are represented in violet color for 400 nm. The treatment with 100% of Imax using 420 nm (blue light) is represented in blue (only for P. fluorescens).
Figure 5
Figure 5
Optical set up: (a) scheme of the set up inside the incubator, (b) mountable matrices used in the experiments, from right to left the light colors are violet, blue, green, yellow and red, (c) set up with liquid-crystal display on the top and (d) cross-section of the set up in which the LED matrices are irradiating the biofilm in the petri dishes.

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