LAUSR

Blue light (BL) has showed bactericidal effectiveness against methicillin-resistant Staphylococcus aureus (MRSA), one of the major clinical pathogens with antibiotic resistance. Bacteria likely respond to the oxidative stress induced by BL, however, the defensive response is still unclear. This study was to reveal the phenotypic change of MRSA after exposed to 15 cycles of sub-lethal blue light illumination. The comparative transcriptomic results showed that the expression of peptidoglycan (PG) synthesis gene glmS was significantly up-regulated in the cells after the multiple cycle light treatment, and the biochemical analysis determined that the content of PG synthesized was increased by 25.86% when compared to that in control cells. Furthermore, significant thickening of the cell wall was observed under transmission electron microscope (P < 0.05). The light sensitivity of the tested MRSA strain was reduced after the multiple cycles light treatment, indicating the possibility of MRSA being more adaptive to the BL stress. The present study suggested that the multiple cycles of sub-lethal BL could change the light susceptibility of MRSA through thickening cell wall.