AUTHOR=Guo Yan-Na , He Ke-Ren , Liang Shao-Shan , Mou Rui-Wei , Lu Meng-Han , He Yong-Ming , Tang Lu-Ping 

TITLE=The effect and mechanism of volatile oil emulsion from leaves of Clausena lansium (Lour.) Skeels on Staphylococcus aureus in vitro

JOURNAL=Frontiers in Microbiology

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2024.1376819

DOI=10.3389/fmicb.2024.1376819

ISSN=1664-302X

ABSTRACT=<p>This study aimed to develop a suitable dosage form of volatile oil from wampee leaves and to explore its antibacterial mechanism <italic>in vitro</italic>. The chemical composition of the volatile oil from wampee leaves was determined by gas chromatography-mass spectrometry (GC-MS). Different microemulsion ratios were tested and their stabilities were investigated to determine the optimal ratio. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the wampee leaves volatile oil emulsion (WVOE) against <italic>Salmonella typhimurium</italic> (<italic>S. typhimurium</italic>) and <italic>Staphylococcus aureus</italic> (<italic>S. aureus</italic>) were determined using double-dilution and plate-counting methods, respectively. Morphological changes in these two bacteria were observed using scanning electron microscopy. Death, ultrastructural morphology, and biofilm formation were also assessed for <italic>S. aureus</italic>. Finally, we established an <italic>S. aureus</italic>-infected Lewis lung carcinoma (LLC) cell model to evaluate the protective effects of the volatile oil emulsion and the associated mechanisms. The volatile oil extracted from wampee leaves contained 37 compounds, of which 96.49% were aromatic hydrocarbons, terpenoids, and their oxygen-containing derivatives. The emulsion was most stable at 1:1 in the oil phase and 1:9 in the water phase. WVOE had poor antibacterial activity against <italic>S. typhimurium</italic>, but the MIC and MBC against <italic>S. aureus</italic> were 312.5 and 2,500 μg/mL, respectively. <italic>S. aureus</italic> survival rates were 84.6%, 14.5%, and 12.8% in the 1/2, 1, and 4 × MIC groups, respectively, compared with 97.2% in the control group. <italic>S. typhimurium</italic> survival was not affected by WVOE treatment. WVOE administration induced cavity formation and abnormal binary fission, and significantly inhibited biofilm formation in <italic>S. aureus</italic> cells. The WVOE notably reduced the number of <italic>S. aureus</italic> and inhibited <italic>TLR4</italic>, <italic>NLRP3</italic>, <italic>NF-κB</italic>, <italic>IL-6</italic>, <italic>IL-18</italic>, and <italic>TNF-α</italic> gene expression in <italic>S. aureus</italic>-infected LLC cells. The WVOE had a significant inhibitory effect on <italic>S. aureus</italic> and altered its cell membrane permeability. Moreover, it alleviated inflammation by inhibiting the NF-κB-NLRP3 pathway in <italic>S. aureus</italic>-infected LLC cells.</p>