Exposure to b-LED Light While Exerting Antimicrobial Activity on Gram-Negative and -Positive Bacteria Promotes Transient EMT-like Changes and Growth Arrest in Keratinocytes.

Nicoletta Mancianti,Flavia Trionfetti,Claudia Montaldo,Valeria De Turris,Paolo Menè,Bruno Casciaro,Michela Terri,Alessandro Domenici,Raffaele Strippoli,Giulio Bontempi,Giammarco Raponi,Maria Luisa Mangoni

doi:10.3390/ijms23031896

Abstract

While blue LED (b-LED) light is increasingly being studied for its cytotoxic activity towards bacteria in therapy of skin-related infections, its effects on eukaryotic cells plasticity are less well characterized. Moreover, since different protocols are often used, comparing the effect of b-LED towards both microorganisms and epithelial surfaces may be difficult. The aim of this study was to analyze, in the same experimental setting, both the bactericidal activity and the effects on human keratinocytes. Exposure to b-LED induced an intense cytocidal activity against Gram-positive (i.e, Staphylococcus aureus) and Gram-negative (i.e., Pseudomonas aeruginosa) bacteria associated with catheter-related infections. Treatment with b-LED of a human keratinocyte cell line induced a transient cell cycle arrest. At the molecular level, exposure to b-LED induced a transient downregulation of Cyclin D1 and an upregulation of p21, but not signs of apoptosis. Interestingly, a transient induction of phosphor-histone γ-H2Ax, which is associated with genotoxic damages, was observed. At the same time, keratinocytes underwent a transient epithelial to mesenchymal transition (EMT)-like phenotype, characterized by E-cadherin downregulation and SNAIL/SLUG induction. As a functional readout of EMT induction, a scratch assay was performed. Surprisingly, b-LED treatment provoked a delay in the scratch closure. In conclusion, we demonstrated that b-LED microbicidal activity is associated with complex responses in keratinocytes that certainly deserve further analysis.

Highlights

Irradiation of P. aeruginosa and S. aureus strains for 4 h with 420 nm blue Light-emitting diodes (LEDs) (b-LED) light resulted in statistically significant bacterial growth suppression when compared with non-irradiated controls in both bacterial strains
The logarithmic reduction of colony forming unit (CFU) in the b-LED treatment of P. aeruginosa was a ~2.1 Log10 CFU/mL, which is equivalent to a bacterial killing value of 99.2%
These results indicate a bactericidal activity of the 420 nm b-LED

Summary

Introduction

Antimicrobial resistance (AMR) is the capacity of a microorganism to acquire the ability to replicate in the presence of a concentration of an antimicrobial agent that would instead be generally sufficient to inhibit or inactivate microorganisms of the same species [1].This is an increasing global health concern with a high epidemiological impact on the whole population (increase in morbidity and mortality), with heavy social and economic burdens (extension of hospital stays/greater use of diagnostic procedures).A study by the European Center for Disease Prevention and Control (ECDC) reports that in 2015, in the countries of the European Union and the European Economic Area, there were 671,689 cases of AMR infections, to which 33,110 deaths were attributable, a third of which occurred in Italy, highlighting the seriousness of the problem in our country.Compared to non-resistant forms, resistant bacteria will double the chances of developing a serious health issue and triple the chances of death [2]. Antimicrobial resistance (AMR) is the capacity of a microorganism to acquire the ability to replicate in the presence of a concentration of an antimicrobial agent that would instead be generally sufficient to inhibit or inactivate microorganisms of the same species [1]. This is an increasing global health concern with a high epidemiological impact on the whole population (increase in morbidity and mortality), with heavy social and economic burdens (extension of hospital stays/greater use of diagnostic procedures). In the US, more than two million infections a year are caused by bacteria that are resistant to at least first-line antibiotic treatments, implying for the US health system 20 billion USD in excess costs each year [3,4]

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