Purpose: This study aimed at identifying a novel plant extract with potential antimicrobial activity against Staphylococcus aureus and methicillin-resistant S. aureus (MRSA), to validate efficacy in a food model, and to elucidate the major volatile composition and antimicrobial mechanism.
Methods: The minimum inhibitory and bactericidal concentrations of four plant extracts (Atuna racemosa AR, Xanthostemon verticillatus XV, Syzygium antisepticum leaf SA-L, and Syzygium antisepticum stem SA-S) were determined against S. aureus and MRSA, using the microdilution method. Anti-staphylococcal activity of SA-L was validated in cooked chicken at 4, 10, and 25°C. SA-L extract volatile composition was determined using GC-MS. The antimicrobial mechanism of the crude extract and its major compound was studied using transmission electron microscopy and flow cytometry, respectively.
Results: Among the four extracts evaluated, SA-L showed the most potent antimicrobial activity against S. aureus and MRSA, with an MIC of 0.13 mg/mL. In a food study, higher SA-L concentration (32 mg/mL) was needed to inhibit or reduce growth of S. aureus and MRSA in cooked chicken, but this caused a color change on meat surface. By GC-MS, caryophyllene (9.19%) was found to be the most abundant volatile compound in SA-L extract. Both crude extract and caryophyllene induced membrane damage in S. aureus. Caryophyllene, alone, showed weaker antimicrobial activities.
Significance: These results demonstrated the antimicrobial properties of S. antisepticum leaf extract against S. aureus and MRSA, identified its major volatile composition, and its membrane-damaging antimicrobial mechanism. However, further work is needed to enhance its antimicrobial activity in food matrices.