Antibacterial activity of hypocrellin A against Staphylococcus aureus

The antibacterial activity and acting mechanism of hypocrellin A (HA) were conducted regarding in vitro activity of HA on Staphylococcus aureus GZ86 by analyzing the growth, permeability, and morphology of the bacterial cells following treatment with HA. The experimental results indicated 1.5 mg/l HA could completely inhibit the growth of 10⁷ CFU/ml S. aureus cells in liquid beef extract-peptone medium under a halogen-tungsten lamp for 120 min. Meanwhile, HA resulted in the leakage of reducing sugars and proteins and induced the respiratory chain dehydrogenases into inactive state, suggesting that HA were able to destroy the permeability of the bacterial membranes. When the cells of S. aureus were exposed to 2.5 mg/l HA under a halogen-tungsten lamp for 120 min, many pits and gaps were observed in bacterial cells by scanning electron microscopy, and the cell wall was fragmentary, indicating the bacterial cells were damaged severely. The experiments strongly confirmed the contribution of multiform reactive oxygen species (ROS) to bactericidal effect. In conclusion, the combined results suggested that ROS may damage the structure of bacterial cell wall and depress the activity of some membranous enzymes, which cause S. aureus bacteria to die eventually.