Abstract
Essential oils (EOs) have aroused attention among the naturally-occurring therapeutic compounds with anti-infective properties. This study examined the chemical composition and the antibacterial potential of EOs from three Lamiaceae species including Ocimum gratissimum (leaves), Plecthrantus epilithicus (leaves), and Satureja robusta (leaves and flowers). EOs were obtained by hydrodistillation using a Clevenger-type apparatus, followed by characterization by gas chromatography-mass spectrometry (GC-MS) and flame ionization detector (GC/FID). The antibacterial efficacy of EOs was screened using the microdilution method, against a panel of eight foodborne bacteria isolates namely Enterobacter cloacae, Yersinia enterocolotica, Klebsiella pneumoniae, Salmonella typhi, Escherichia coli, Citrobacter freundii, Shigella flexneri, and Enterococcus faecalis. GC-MS and GC/FID analysis led to the identification of 53 components from EOs of P. epilithicus, while around forty compounds have been characterized from the EOs of O. gratissimum (43), leaves of Satureja robusta (43), and flowers of S. robusta (44). The nature of identified compounds varied according to the species. The most prevalent volatile compounds identified in the EOs of P. epilithicus were piperitenone oxide (23.65%) and two isomers piperitone oxide 2/2 (16.15%) and piperitone oxide 1/2 (7.24%). The major constituents in the EOs of leaves of O. gratissimum were elemicin (33.474%) and eugenol (30.258%). Piperitone oxide, piperitone, and germacrene D were identified as major constituents in both the EOs of leaves of S. robusta (28.3%, 15.14%, and 9.42% respectively) and flowers (45.6%, 11.55%, and 3.94% respectively). The oils displayed selective antibacterial potential, with the recorded minimal inhibitory concentration (MIC) values ranging from 0.0156 to 1% (v/v). EOs of P. epilithicus as well as that of the leaves and flowers of S. robusta acted against all studied bacteria. Most of the MIC values were below 0.25% (v/v), indicating a strong inhibitory potential of studied EOs. The present study provides a strong baseline for consideration of the EOs from O. gratissimum, S. robusta, and P. epilithicus in the control of bacterial foodborne infections.
Highlights
Numerous investigations showed evidence of the pharmacological properties of medicinal plants and derived products
Our study focused on three Lamiaceae plant species growing in Cameroon, namely Ocimum gratissimum, Satureja robusta, and Plecthrantus epilithicus
The plant parts have been carefully identified and authenticated at the National Herbarium of Cameroon (HNC) where voucher specimens were deposited under registration numbers (O. gratissimum 23798HNC, P. epilithicus 9729HNC, and S. robusta 12777 SFRCAM)
Summary
Numerous investigations showed evidence of the pharmacological properties of medicinal plants and derived products. Essential oils may be derived from specialized cells or groups within particular regions of the plant, such as stems, leaves, the foliage, bark, wood, fruit, seeds, and rhizomes During several civilizations, they have been exploited worldwide in folk medicine, owing to their pharmacological properties [4]. Plant essential oils have aroused attention among the naturally-occurring therapeutic agents with anti-infective activity Several among these secondary plant metabolites exhibit marked antimicrobial effects that have made their use as an antiseptic and/or preservative in food well known, since antiquity [5]. In addition to their antimicrobial properties, numerous investigations documented the therapeutic uses of essential oils including anti-parasitic, analgesic, antioxidant, antiinflammatory, anti-obesity, anticancer, wound-healing, antispasmodic, allelochemicals properties, and many more [2, 6]. Relative modes of action have been unveiled along with pharmacological targets, though the shortage of human studies restraints the potential of essential as efficient and safe phytotherapeutic agents [6]
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