Antimicrobial Activities of Magnolol and Honokiol against Streptococcus Mutans

Objectives: Magnolia officinalis, a kind of traditional Chinese medicine, are used as an anti-allergic and anti-asthmatic compound with a wide spectrum of pharmacological activities. The purpose of this study was to investigate magnolol and honokiol found in Magnolia offinalis on the growth and cell membrane and cell morphology of streptococcus mutans. Methods: The microorganisms used in this study were Streptococcus mutans ATCC 25175. Magnolol and honokiol were extracted from Magnolia officinalis and their antimicrobial activity was assessed by determination of MIC and MBC, and the effect of on the kinetic of time-killing was also examined. The leakage of K2+ from streptococcus mutans cells has been evaluated by atomic absorption spectrometer. To further confirm whether the bacterial surfaces were the target of Magnolol and Honokiol, scanning electronic microscope (SEM) was used to get the image of bacteria after treatment with Magnolol and Honokiol. Results: Both Magnolol and Honokiol exhibited remarkable antimicrobial activity against streptococcus mutans (MIC of 7.8 µg /mL and 31.3 µg /mL; MBC of 62.5µg /mL and 125µg /mL) and fast killing rate. Magnolol and Honokiol can lead to K2+ leakage of streptococcus mutans cells, the leakage increased as the drug concentration increased. No obvious alterations in the surface morphology of streptococcus mutans cells were observed under SEM in Magnolol and Honokiol groups of either concentration. Cells were smooth, plump and located in chains, suggested that the Magnolol and Honokiol has not destroyed cell wall obviously. Conclusion: Magnolol and honokiol present remarkable antimicrobial activity against streptococcus mutans, which may target on ion channels of cell membrane. Further studies on this aspect should be carried out. Support for this study is provided from Chinese Natural Science Grant (Grant No.30572409)