Antibacterial and Antibiofilm Activity of <i>Clerodendron Cyrtophyllum</i> Turcz. Ethanolic Extracts against <i>Staphylococcus aureus</i> from Bovine Mastitis

Bovine mastitis causes huge economic losses for the dairy industry worldwide. <i>Staphylococcus aureus</i> (<i>S. aureus</i>) is an important pathogen that induces bovine mastitis, and its resistance to antibiotics has become a severe problem in bovine mastitis therapy. Therefore, the development of new treatments for this potentially fatal infection is urgently needed. <i>Clerodendron cyrtophyllum</i> Turcz. is a traditional Chinese medicine that has been used for the treatment of various diseases. However, its antibacterial effect on <i>S. aureus</i> in bovine mastitis is rarely investigated. In this study, <i>Clerodendron cyrtophyllum</i> ethanolic extract (CTE) was prepared, and its <i>S. aureus</i>-inhibting activities and antibiofilm effects were determined. The mechanisms of CTE against <i>S. aureus</i> were also investigated. The results showed that the growth of <i>S. aureus</i> was inhibited by CTE, and the minimum inhibitory concentration (MIC) of CTE was 250 μg/ml. After treatment with CTE, extracellular alkaline phosphatase (AKP), protein, and nucleic acid of <i>S. aureus</i> were increased, suggesting that the permeability of <i>S. aureus</i> cells was enhanced. Furthermore, intracellular reactive oxygen species (ROS) in <i>S.</i> aureus were increased, suggesting that CTE inhibited <i>S. aureus</i> growth by causing oxidative damage. In addition, CTE treatment suppresses biofilm formation of <i>S. aureus</i>, as almost 50% of biofilm was scavenged at 2× (MIC) of CTE. After CTE treatment, <i>icaA</i>, <i>sarA</i>, and <i>sigB</i> mRNA levels were significantly downregulated, whereas the <i>icaR</i> mRNA level was significantly upregulated, indicating that CTE suppressed biofilm formation by regulating expression of the biofilm formation-related genes. The findings of this study indicate that CTE could be a potential treatment for bovine mastitis-associated <i>S. aureus</i>.