Assessment of the potential for resistance to antimicrobial violet-blue light in Staphylococcus aureus

Tomb, R. M., Maclean, M., Coia, J. E., MacGregor, S. J. and Anderson, J. G. (2017) Assessment of the potential for resistance to antimicrobial violet-blue light in Staphylococcus aureus. Antimicrobial Resistance and Infection Control, 6, 100. (doi: 10.1186/s13756-017-0261-5) (PMID:29046782) (PMCID:PMC5639585)

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Background: Antimicrobial violet-blue light in the region of 405 nm is emerging as an alternative technology for hospital decontamination and clinical treatment. The mechanism of action is the excitation of endogenous porphyrins within exposed microorganisms, resulting in ROS generation, oxidative damage and cell death. Although resistance to 405 nm light is not thought likely, little evidence has been published to support this. This study was designed to establish if there is potential for tolerance development, using the nosocomial pathogen Staphylococcus aureus as the model organism. Methods: The first stage of this study investigated the potential for S. aureus to develop tolerance to high-intensity 405 nm light if pre-cultured in low-level stress violet-blue light (≤1 mW/cm2 ) conditions. Secondly, the potential for tolerance development in bacteria subjected to repeated sub-lethal exposure was compared by carrying out 15 cycles of exposure to high-intensity 405 nm light, using a sub-lethal dose of 108 J/cm2 . Inactivation kinetics and antibiotic susceptibility were also compared. Results: When cultured in low-level violet-blue light conditions, S. aureus required a greater dose of high-intensity 405 nm light for complete inactivation, however this did not increase with multiple (3) low-stress cultivations. Repeated sub-lethal exposures indicated no evidence of bacterial tolerance to 405 nm light. After 15 sub-lethal exposures 1.2 and 1.4 log10 reductions were achieved for MSSA and MRSA respectively, which were not significantly different to the initial 1.3 log10 reductions achieved (P = 0.242 & 0.116, respectively). Antibiotic susceptibility was unaffected, with the maximum change in zone of inhibition being ± 2 mm. Conclusions: Repeated sub-lethal exposure of non-proliferating S. aureus populations did not affect the susceptibility of the organism to 405 nm light, nor to antibiotics. Culture in low-level violet-blue light prior to 405 nm light exposure may increase oxidative stress responses in S. aureus, however, inactivation still occurs and results demonstrate that this is unlikely to be a selective process. These results demonstrate that tolerance from repeated exposure is unlikely to occur, and further supports the potential development of 405 nm light for clinical decontamination and treatment applications.

Item Type:Articles
Additional Information:RMT would like to thank the Scottish Infection Research Network and Chief Scientist Office for their funding support through a Doctoral Fellowship Award, CSO Reference: SIRN/DTF/13/02.
Glasgow Author(s) Enlighten ID:Coia, Dr John
Authors: Tomb, R. M., Maclean, M., Coia, J. E., MacGregor, S. J., and Anderson, J. G.
College/School:College of Medical Veterinary and Life Sciences > School of Medicine, Dentistry & Nursing
Journal Name:Antimicrobial Resistance and Infection Control
Publisher:BioMed Central
ISSN (Online):2047-2994
Copyright Holders:Copyright © 2017 The Authors
First Published:First published in Antimicrobial Resistance and Infection Control 6: 100
Publisher Policy:Reproduced under a Creative Commons License

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