Hypericin-mediated photodynamic antimicrobial effect on clinically isolated pathogens

The aim of this study was to determine the photodynamic antimicrobial effect of hypericin on clinically isolated Staphylococcus aureus and Escherichia coli cells. Bacterial cells (10 8 cells per mL) were incubated with hypericin (0-40 μm) for 30 min and followed by light irradiation of 600-800 nm at 5-30 J cm -2. Cell survival was determined by colony counting, cellular hypericin uptake examined by flow cytometer, and cell membrane damage examined by scanning electron microscopy and leakage assay. The effectiveness of hypericin-mediated photodynamic killing was strongly affected by cellular structure and photosensitizer uptake. The combination of hypericin and light irradiation could induce significant killing of Gram positive methicillin-sensitive and -resistant S. aureus cells (>6 log reduction), but was not effective on Gram negative E. coli cells (<0.2 log reduction). The difference was caused by different cell wall/membrane structures that directly affected cellular uptake of hypericin. Increasing prevalence of antibiotic-resistant bacteria is one of the most pressing global health issues. It is imperative to develop nonantibiotic approaches for combating antibiotic-resistant bacterial infections. Photodynamic antimicrobial chemotherapy (PACT) is a promising alternative. This study examined the effect of hypericin-mediated PACT on clinically isolated S. aureus and E. coli. Hypericin-mediated PACT could induce significant killing of Gram positive methicillin-sensitive and methicillin-resistant S. aureus cells (illustrated), but was ineffective on Gram negative E. coli cells. This phenomenon is due to the differences in bacterial wall/membrane structures that directly affect cellular uptake of hypericin.Department of Health Technology and Informatic