Antibacterial Activity and Stability of Hepu Pearl Extracts on the Staphylococcus aureusin in Vitro

Objective:To study the antibacterial activity and stability of Hepu pearl extracts against standard strains of Staphylococcus aureus (S. aureus) in vitro. Method:The bacteriostatic zone size and minimum inhibitory concentration (MIC) of Hepu pearl extracts on S. aureus were determined by Oxford cup method and 96-well method. The effects of temperature, repeated freezing and thawing, acid-base, ultraviolet, metal ion, trypsin and pepsin on the antibacterial activity of Hepu pearl extracts were studied. Results:The Hepu pearl extracts had significant antibacterial activity against S. aureus, and the minimum inhibitory concentration was 0.94 mg·mL^-1, and the antibacterial activity showed a dose-dependent effect. The bacteriostatic stability experiment of 8×MIC Hepu pearl extracts was carried out, and the OD₆₀₀ value of S. aureus was used as an index. The results showed that the antibacterial activity of Hepu pearl extracts remained stable in pH3.0~9.0, but about 70% in pH11.0 retained compared with pH7.0. The antibacterial activity remained stable at-80℃, but about 68% retained at 100℃ compared with 4℃. Under the condition of repeated freezing and thawing at-20℃ and irradiated by 20 W UV lamp, the antibacterial activity of the extracts remained good stability. Under the conditions of NaCl, KCl and CaCl₂ of 25~200 mmol·L^-1, the antibacterial activity of the extracts was stable. While under the condition of 25~200 mmol·L^-1 MgCl₂, the antibacterial activity decreased gradually, and the antibacterial activity was retained by about 40% compared with the non-added group at 200 mmol·L^-1 MgCl₂. The extracts maintained good bacteriostatic stability to trypsin treatment, but the antibacterial activity disappeared under pepsin treatment, indicating that it was sensitive to pepsin. Conclusion:Hepu pearl extracts had stable inhibitory activity against S. aureusin in vitro, which would provide a theoretical basis for its application and development in food industry in the future.