var. Flower Essential Oil Reduces MRSA Pathogenicity by Inhibiting Virulence Gene Expression.

The essential oil extracted from the flowers of var. (Maxim.) Kitam (CZEO), family Asteraceae, was investigated to determine its ability to inhibit the pathogenicity of methicillin-resistant (MRSA). The chemical composition of CZEO was analyzed using gas chromatography-flame ionization detector and gas chromatography-mass spectrometry, and 88 compounds were identified and categorized as monoterpenes (68.82%), sesquiterpenes (17.82%), and others (5.01%). CZEO inhibited MRSA floating cell growth, acid production, and biofilm formation in a concentration-dependent manner. Furthermore, confocal laser scanning and scanning electron microscopy confirmed that the CZEO treatment decreased MRSA viability and notably reduced the three-dimensional density of the biofilm. Real-time PCR demonstrated that the mRNA expression of the MRSA gene A (), accessory gene regulator A (), staphylococcal accessory regulator A (), and staphylococcal enterotoxin A (), which are pivotal genes implicated in MRSA pathogenicity, declined in a concentration-dependent manner following the CZEO treatment compared with the control. Thus, CZEO appeared to directly target the pathogenicity MRSA regulators. These findings substantiate the potential of CZEO as a natural antimicrobial agent for preventing MRSA infections.