Actions of farnesol and xylitol against Staphylococcus aureus.

BACKGROUND: Heavy colonization of atopic dermatitis (AD) with Staphylococcus aureus is well documented. The isolation rate of methicillin-resistant S. aureus is high in strains from AD in Japan. Our objective in the present study was to investigate the actions of farnesol and xylitol against S. aureus for the control of AD skin lesion-colonizing S. aureus. METHODS: We examined the actions of farnesol on plasma coagulation and superantigenic exotoxin production by S. aureus, the antimicrobial activity of beta-lactam antibiotics combined with farnesol at concentrations below the minimal inhibitory concentration (MIC) and the effect of xylitol on glycocalyx production. RESULTS: Coagulation by S. aureus cells was inhibited in plasma containing farnesol at a concentration of 1/12 of the MIC (100 microg/ml) after incubation for 24 h. The production of superantigenic exotoxins by S. aureus cells with farnesol (100 microg/ml) was about 10 times lower than that by S. aureus cells alone. The MICs of ampicillin and cefdinir against S. aureus were reduced to < or =0.06 microg/ml in Mueller-Hinton agar plates with farnesol (100 microg/ml). We suggest that farnesol at concentrations above the MIC had a suppressive effect against S. aureus cells in the exponential and stationary phase and acted on the cell wall of S. aureus cells in both phases. CONCLUSIONS: Farnesol is a promising adjuvant agent against S. aureus skin infections treated with beta-lactam antibiotics. Further, 5% xylitol inhibited glycocalyx production by S. aureus cells and consequently had a suppressive effect on the colonization of S. aureus on the horny cells of AD lesions.