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Front. Physiol. | doi: 10.3389/fphys.2018.01658

Changes of Intracellular Porphyrin, Reactive Oxygen Species and Fatty Acids Profiles during Inactivation of Methicillin-Resistant Staphylococcus aureus by Antimicrobial Blue Light

Jiaxin Wu1, Zhaojuan Chu1,  Zheng Ruan2*, Xiaoyuan Wang1, Tianhong Dai3 and  Xiaoqing Hu1*
  • 1Jiangnan University, China
  • 2Nanchang University, China
  • 3Harvard Medical School, United States

Antimicrobial blue light (aBL) attracted increasing interest for antimicrobial properties. However, the underlying bactericidal mechanism needed to be verified. The hypothesis included the excitation of intracellular chromophores by aBL, subsequent generation of reactive oxygen species (ROS) and the resultant oxidization of various biomolecules. Thus, detecting the changes of intracellular biomolecules such as coproporphrin, singlet oxygen and ROS would help to uncover the physiological change and to confirm the underlying mechanism. Furthermore, it is of great significance to reveal novel targets of ROS, such as fatty acids. Therefore, these innovative works on methicillin-resistant Staphylococcus aureus (MRSA) were carried out in the current study. The results showed that aBL (5-80 J/cm2) exhibited bactericidal effect on MRSA, and almost no bacteria survived when 80 J cm2 had been delivered. Later, it was revealed that the concentration changes of intracellular molecules were associated with aBL irradiation. Firstly, coproporphyrin was decreased gradually, and meanwhile, ROS was increased rapidly. Especially, the emergence and increase of singlet oxygen were imaged, supporting the hypothesis. The severe oxidative stress resulted in the simultaneous increase of the lipid oxidative product MDA and intracellular K+ leakage, indicating the damage on lipids and permeability of cell membrane. More roughness on cell surface was also observed by atomic force microscope. All data above proved that cell membrane was target of ROS during aBL irradiation. Finally, to discover the target biomolecules, the fatty acids profiles at different illumination levels were compared by GC-MS. The relative content of three unsaturated fatty acids (C16:1, C20:1 and C20:4) were decreased and disappeared along with aBL irradiation, which likely played a key role in membrane injuries. The current study verified the changes of the intracellular biomolecules and revealed that lipids especially the unsaturated fatty acids in cell membrane lipids were target of ROS during aBL inactivation.

Keywords: Antimicrobial blue light, Methicillin-resistant Staphylococcus aureus (MRSA), Coproporphyrin, Unsaturated fatty acids, Membrane injuries, Lipid

Received: 28 Jul 2018; Accepted: 02 Nov 2018.

Edited by:

Huang Chiao Huang, University of Maryland, United States

Reviewed by:

Junming Ren, City of Hope National Medical Center, United States
Yixia Yin, Brigham and Women's Hospital, Harvard Medical School, United States  

Copyright: © 2018 Wu, Chu, Ruan, Wang, Dai and Hu. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence:
Prof. Zheng Ruan, Nanchang University, Nanchang, 330031, Jiangxi Province, China,
Prof. Xiaoqing Hu, Jiangnan University, Wuxi, China,