Sub-Inhibitory Concentrations of Sodium Houttuyfonate in Combination with Erythromycin Inhibit Biofilm Formation and Expression of IcaA in Staphylococcus epidermidis

Background: Staphylococcus epidermidis is an important opportunistic pathogenic bacterium causing infections on implanted medical devices by biofilm formation. Sodium houttuyfonate (SH), which is the active modified compound of Houttuynia cordata is commonly applied for treating chronic bronchitis, purulent skin infections, and respiratory tract infections in China. Objectives: We aimed to investigate the in vitro effects of SH in combination with erythromycin on the production of IcaA and expression of icaA to shed the light on the mechanism of SH and erythromycin in inhibiting biofilm formation of S. epidermidis. Methods: The morphology of the biofilm of S. epidermidis was examined under a scanning electron microscope. Furthermore, inhibitory effects of SH and erythromycin on the production of IcaA and the expression of icaA were detected by Western blotting and quantitative reverse transcription PCR, respectively. Results: First, the morphological results indicated that combing SH and erythromycin at sub-MIC concentrations can effectively inhibit biofilm formation of S. epidermidis. Furthermore, our presented results showed that combing SH and erythromycin at sub-MIC concentration can significantly downregulate the expression of icaA and repress the protein production of IcaA at irreversible attachment and maturation stages of biofilm formation of S. epidermidis. Conclusions: Therefore, our findings suggest that the potent antibiofilm activity of SH in combination with erythromycin against S. epidermidis may be partially due to inactivation of icaA.