Abstract:[Objective]This study explored the effects of critical environmental factors [water activity (aw), pH, and temperature] on the antimicrobial activity of ε-poly-L-lysine (ε-PL), aiming to provide a basis for the application of ε-PL.[Method]With Staphylococcus aureus as an indicator strain, the micro-broth dilution and agar dilution methods as well as antimicrobial growth kinetics were utilized to determine the antimicrobial activity of ε-PL. The protein leakage assay was employed to evaluate the bacterial membrane disruption activity of ε-PL. Live/Dead fluorescence staining was performed to observe the bacterial membrane permeability.[Result]The minimum inhibitory mass concentration (MIC) of ε-PL against Staphylococcus aureus was 40.0 μg/mL. The agar dilution method results indicated that the antimicrobial activity of ε-PL increased with the increase in aw. Additionally, ε-PL demonstrated strong antimicrobial activity at pH 5.0~7.0, moderate antimicrobial activity at pH 4.0, weak antimicrobial activity at pH 8.0, and no antimicrobial activity at pH 9.0,while the maximum antimicrobial activity of ε-PL occurred at 30 ℃ under neutral conditions. The antimicrobial kinetic results showed that the antimicrobial efficacy of ε-PL under different pH conditions was consistent with the agar dilution method results, with strong inhibitory effects at 25 ℃ and 30 ℃ under neutral conditions. ε-PL had strong membrane disruption activity on Staphylococcus aureus under weakly acidic to neutral conditions (pH 5.0~7.0), and the membrane disruption activity of ε-PL was more pronounced at low temperatures (25~30 ℃) and weak at high temperatures (30~35 ℃). The Live/Dead fluorescence staining showed that the bacterial membrane permeability was enhanced by ε-PL at pH 4.0, while little effect was observed at pH 9.0.[Conclusion]The environmental factors aw, pH, and temperature demonstrate significant influences on the antimicrobial activity of ε-PL.
