Kampo medicines suppress the production of exfoliative toxins causing impetigo in Staphylococcus aureus.

An alternative approach, such as antivirulence therapy that modulates the production of bacterial toxins or virulence factors, is necessary to tackle the emergence of antimicrobial-resistant strains. Here, we investigated the potential antivirulence effects of seven Kampo medicines (Jumihaidokuto, Eppikajutsuto, Jizusoippo, Shomakakkonto, Sammotsuogonto, Hainosankyuto and Inchinkoto) against exfoliative toxin (ET)-positive Staphylococcus aureus, which is the major causative agent of impetigo. A growth inhibition assay showed that all of the selected Kampo medicines inhibited the growth of S. aureus at 1/5 (2.5 mg/mL) or less of the conventionally used concentrations. Among these, Jizusoippo and Inchinkoto (0.25-1 mg/mL) suppressed the production of ET without inhibiting the bacterial growth. Furthermore, Jizusoippo and Inchinkoto significantly suppressed the expression of ET genes in a concentration-dependent manner. Our findings strongly suggest, for the first time, that Kampo medicines, especially Jizusoippo and Inchinkoto, have the potential to serve as antivirulence agents against skin infections caused by S. aureus by suppressing the production of ET.