Bactericidal activity of herbal volatile oil extracts against multidrug-resistant Acinetobacter baumannii

The aim of the study is to investigate the antibacterial activity of 10 volatile oils extracted from medicinal plants, including galangal (Alpinia galanga Linn.), ginger (Zingiber officinale), plai (Zingiber cassumunar Roxb.), lime (Citrus aurantifolia), kaffir lime (Citrus hystrix DC.), sweet basil (Ocimum basilicum Linn.), tree basil (Ocimum gratissimum), lemongrass (Cymbopogon citratus DC.), clove (Syzygium aromaticum), and cinnamon (Cinnamomum verum) against four standard strains of Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii, and 30 clinical isolates of multidrug-resistant A. baumannii (MDR-A. baumannii).

Agar diffusion, minimum inhibitory concentration, and minimum bactericidal concentration (MBC) were employed for the determination of bactericidal activity of water distilled medicinal plants. Tea tree oil (Melaleuca alternifolia) was used as positive control in this study.

The results indicated the volatile oil extracted from cinnamon exhibited potent antibacterial activity against the most common human pathogens, S. aureus, E. coli, P. aeruginosa, and A. baumannii. Most of volatile oil extracts were less effective against non-fermentative bacteria, P. aeruginosa. In addition, volatile oil extracted from cinnamon, clove, and tree basil possessed potent bactericidal activity against MDR-A. baumannii with MBC₉₀ of 0.5, 1, and 2 mg/mL, respectively.

The volatile oil extracts would be useful as alternative natural product for the treatment of the most common human pathogens and MDR-A. baumannii infections.