Antibacterial effects of the essential oil from flower buds of Magnolia biondii Pamp

Flower buds of Magnolia biondii Pamp (family Magnoliaceae) is known as Xin-Yi in the Chinese Pharmacopoeia, and is widely used for the treatment of allergic rhinitis, rhinosinusitis, nasal congestion, and headache.¹ Bacterial infection caused by Staphylococcus aureus in the-nasal-sinus mucosa is one of key factors which could cause rhinosinusitis,² thus it is important to evaluate the antibacterial effect of the extracts from M. biondii, which may provide scientific evidence of using Xin-Yi for the treatment of rhinosinusitis. In this study, the essential oil and lignan-rich extract isolated from the flower buds of Magnolia biondii Pamp (Xin-Yi) were investigated for their chemical compositions and in vitro antibacterial activities. GC-MS analysis of the Magnolia essential oil disclosed the presence of 56 compounds including camphor (10.6%), eucalyptol (25.0%), linalool (5.8%), terpine-4-ol (8.4%), alpha-terpineol (19.8%), alpha-cadinol (3.3%), citronellol (2.9%), geraniol (2.3%), and trans-farnesol (8.7%). Both GC-MS and NMR analyses of the chloroform extract disclosed the presence of 7 tetrahydrofurofuran lignans that were demethoxyaschantin, fargesin, epieudesmin, eudesmin, aschantin, magnolin, and yangambin. The essential oil showed stronger antibacterial activities than the lignan-rich extract against five bacteria including pathogenic Staphylococcus aureus and S. epidermidis with MICs ranging from 250 to 500 µg ml^-1 using microplate Alamar blue assay. Time-kill kinetics was used to monitor the survival characteristics of S. aureus and Escherichia coli in the presence of the essential oil over 24 hours, which indicated rapidly bactericidal effects. Scanning electron microscopy (Figure 1) showed the change of morphological appearance of S. aureus through destruction its cell wall and membrane by the Magnolia oil.

Fig. 1: Scanning electron micrograph of control S. aureus at 1 hour of incubation at 37 °C (A). Scanning electron micrograph of S. aureus after exposure to Magnolia oil (2 MIC) for 1h (B). Scanning electron micrograph of S. aureus after exposure to Magnolia oil (2 MIC) for 24h (C). Arrows show lysis of cells and leakage of cellular contents.

Acknowledgements: This work was supported by MOHSER: Ministry Of Higher Education and Scientific Research/IRAQ (A PhD studentship to Omar Aldulaimi). We are grateful to Nigel Bowers and Prof. Paul Horrocks for their assistance in antimicrobial assay, and Karen Walker and Prof. David Furness for their help with SEM.

Keywords: Magnolia biondii Pamp, essential oils, GC-MS, time-kill assay, scanning electron microscopy, Staphylococcus aureus.

References:

[1] Shen Y, Li CG, Zhou SF, Pang EC, Story DF, Xue CC. Chemistry and bioactivity of Flos Magnoliae, a Chinese herb for rhinitis and sinusitis. Cur Med Chem 2008; 15: 1616 – 1627

[2] Redinbo MR. The microbiota, chemical symbiosis, and human disease. J Mol Biol 2014; 426: 3877 – 3891