https://www.selleckchem.com/products/skl2001.html (3) Exogenous FMN or FAD, which strongly absorb 450nm light, did not promote the antimicrobial effect of PBL, neither did exogenous NAD or NADH, two weak blue light-absorbing photosensitizers. These results strengthen our previous assertion that an endogenous chromophore with the capacity to absorb and transform light energy into a biochemical process that engenders bacterial cell death, is essential for 450nm PBL to suppress GBS. These results strengthen our previous assertion that an endogenous chromophore with the capacity to absorb and transform light energy into a biochemical process that engenders bacterial cell death, is essential for 450 nm PBL to suppress GBS. In a recent study we showed that blue light inactivates methicillin-resistant Staphylococcus aureus (MRSA) by perturbing, depolarizing, and disrupting its cell membrane. The current study presents visual evidence that the observed biochemical changes also result in cell metabolic changes and structural alteration of the cell membrane. Cultures of MRSA were treated with 450nm pulsed blue light (PBL) at 3mW/cm irradiance, using a sub lethal dose of 2.7J/cm radiant exposure three times at 30-min intervals. Following 24h incubation at 37°C, irradiated colonies and control non-irradiated colonies were processed for light and transmission electron microscopy. The images obtained revealed three major effects of PBL; (1) disruption of MRSA cell membrane, (2) alteration of membrane structure, and (3) disruption of cell replication. These signs of bacterial inactivation at a dose deliberately selected to be sub-lethal supports our previous finding that rapid depolarization of bacterial cell membrane and disruption of cellular function comprise another mechanism underlying photo-inactivation of bacteria. Further, it affirms the potency of PBL. These signs of bacterial inactivation at a dose deliberately selected to be sub-lethal supports our previous finding that