Chamaecyparis obtusa Essential Oil Inhibits Methicillin-Resistant Staphylococcus aureus Biofilm Formation and Expression of Virulence Factors

The emergence of antibiotic-resistant bacteria has caused difficulty in treating infectious diseases. Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most commonly recognized antibiotic-resistant bacteria. Novel antibiotics are urgently required to treat these bacteria. Raw materials derived from natural sources can be used for the development of novel antibiotics, such as Chamaecyparis obtusa (C. obtusa), which has been traditionally used in treating asthmatic disease. In this study, the antibacterial activity of the essential oil (EO) extracted from C. obtusa leaves against MRSA was investigated. MRSA growth and acid production from glucose metabolism were inhibited at concentrations greater than 0.1 mg/mL C. obtusa EO. MRSA biofilm formation was observed using scanning electron microscopy and safranin staining. C. obtusa EO inhibited MRSA biofilm formation at concentrations greater than 0.1 mg/mL. Using real-time polymerase chain reaction, mRNA expression of virulence factor genes, sea, agrA, and sarA, was observed. agrA expression was inhibited with C. obtusa EO concentrations greater than 0.2 mg/mL, whereas inhibition of sea and sarA expression was also observed at a concentration of 0.3 mg/mL. C. obtusa EO was analyzed by gas chromatography (GC) and GC coupled for mass spectrometry, which identified 59 constituents, accounting to 98.99% of the total EO. These findings suggest that C. obtusa EO has antibacterial effects against MRSA, which might be associated with the major components of C. obtusa EO, such as sabinene (19.06%), alpha-terpinyl acetate (16.99%), bornyl acetate (10.48%), limonene (8.54%), elemol (7.47%), myrcene (5.86%), gamma-terpinene (4.04%), and hibaene (3.01%).