Ketema Tolossa, Kaleab Asres,* Fathy K. El-Fiky, Abdel Nasser B. Singab and Franz Bucar

Abstract: The essential oils of fresh aerial parts of Satureja abyssinica (Benth.) Briq. ssp. abyssinica and Satureja paradoxa (Vatke) Engl. collected in Ethiopia were analyzed by gas chromatography (GC/FID) and gas chromatography–mass spectrometry (GC/MS). The results of the analyses indicated that the components of the two oils are similar qualitatively with significant quantitative differences. Twenty-three compounds comprising 96.9% of the total peak area were identified in S. abyssinica ssp. abyssinica oil with the monoterpene ketones pulegone (43.5%) and isomenthone (40.7%) as major components. The oil of S. paradoxa was found to contain twenty-six compounds comprising 92.0% of the total oil with the major components being cis-piperitone oxide (45.3%), pulegone (9.3%) and piperitenone oxide (8.1%). The in vitro antimicrobial activity of the oils was studied against some medically important pathogens including Gram positive and Gram negative bacteria as well as some fungal strains using standard agar-well diffusion technique. Both oils exhibited significant activity against most of the bacteria and fungi used in the study with minimum inhibitory concentration (MIC) values ranging from 0.50 to 4.00 μL/mL, against the bacteria, and 0.19 to 3.00 μL/mL, against the fungi. Comparison of their activity with standard antibacterial and antifungal agents revealed that both oils were more active against Streptococcus pyogenes than the standard antibiotic amoxicillin. Moreover, the oil of S. paradoxa displayed a powerful activity against Candida albicans and Trichophyton mentagraphytes with growth inhibition zone greater than that of the standard antifungal agent ketoconazole. The oils were also tested for their antioxidant activity in diphenylpicrylhydrazyl (DPPH) assay and showed a dose dependant free radical scavenging activity with IC50 values of 1.8 μL/mL (S. abyssinica subsp. abyssinica) and 1.6 μL/mL (S. paradoxa).

The genus Satureja belongs to the family Lamiaceae (Labiatae). Members of the genus are perennial herbs growing in temperate, tropics, subtropics and Mediterranean climatic areas. In Ethiopia, the genus is represented by eight species (1,2). Several Satureja species contain essential oils which exhibit potential therapeutic activities such as antimicrobial (3–8), antioxidant (9,10), antinociceptive and anti-inflammmatory (11), vasodilatory (12), antispasmodic and antidiarrhoeial (13), analgesic (14), and antidiabetic, antihyperlipidemic and stimulation of reproduction (10). Satureja abyssinica ssp. abyssinica is an annual or perennial herb indigenous to Ethiopia where it is locally known as “Mutansa”. The plants possess distinctive pink flowers and are known to grow on the sides of stony mountains to about 5–80 cm in height (2). All the flowers of this subspecies possess pedicels which makes them different from the other subspecies (subspecies condensata) whose flowers are nearly sessile, in dense verticillasters. In Ethiopian traditional medicine various preparations made from the aerial parts of S. abyssinica ssp. abyssinica are used to relieve headache, stop menstruation, relieve stomach pains, and treat various infectious diseases and skin inflammations (1). Satureja paradoxa is a perennial herb endemic to Ethiopia where it is known to grow on moist soil in open and shady grassland in forests and rarely in tea plantations. The plant which possesses dark violet colored flowers often attains a height of 20–40 cm and is more commonly known by its vernacular name “Naddo”. Due to its strong minty fragrance and claimed antiseptic and disinfectant actions, local people widely use the whole plant for washing milk pots and also to cure skin infections (1). Despite the wide usage of these two plants in the Ethiopian traditional medicine, there appears to have been no chemical or biological studies published on either of them. In the present study the chemical composition of the oils of S. abyssinica subsp. abyssinica and S. paradoxa were analyzed by GC and GC/MS and the oils were further investigated for their antimicrobial activities against various strains of pathogenic bacteria and fungi. In addition, the oils were assessed for their free radical scavenging activity using diphenylpicrylhydrazyl (DPPH) assay method.