Antimicrobial activities of the essential oils of endemic Stachys rupestris and Stachys amanica against multi-resistant bacteria.

Sir,

The global issue of emerging resistant infections has led to the search for new antimicrobial agents. Medicinal plants are a source of renewed interest as ma ny of them have been used in folk medicine to treat infections. Pharmacological studies have confirmed that the extracts or components of the plants belonging to the genus Stachys exert significant antimicrobial effects.[12] Of them, Stachysrupestris (Montbret et Aucher ex Bentham) and Stachysamanica (P.H. Davis) are indigenously found in South Anatolia in Turkey.[3] The Stachys species have been reported to treat genital tumors, sclerosis of the spleen, inflammatory tumors, and cancerous ulcers.[4] However, their antimicrobial activity has not been documented. In this study, the essential oils of S. rupestris and S. amanica against different microorganisms, including multi-resistant bacteria, were evaluated for their antimicrobial activity.

The specimens of S. rupestris and S. amanica were collected at the flowering stage during the months of April–July from Kahramanmaras, Turkey and a sample of each was deposited in the herbarium of the Faculty of Science, University of Mugla, Turkey (Herbarium No: O.V. 2378 and O.V. 2379). The essential oils of the dried aerial parts were obtained via hydrodistillation by using a Clevenger-type apparatus for four hours. The antimicrobial activity of the essential oils of S. rupestris and S. amanica were tested in vitro by using the paper disc diffusion method. In this study, two gram-negative standard test bacteria, six gram-positive standard test bacteria, ninemulti-resistant bacteria,and yeastwere used. The results obtained in the evaluation of the antimicrobial activity of the essential oils are shown in Table 1.

Table 1

Antimicrobial activity of the essential oils of S. rupestris and S. amanica

The essential oils of S. rupestris and S. amanica showed greater activity against the gram-positive than gram-negative bacteria. The essential oils of S. rupestris inhibited all the gram-positive bacteria, except Staphylococcus epidermidis MU 30. The essential oils of S. amanica were active against all the gram-positive bacteria, except S. epidermidis MU 30 and Staphylococcus aureus MU 38. However, in the gram-negative bacteria, the two essential oils inhibited only the growth of Cryseomonasluteola MU 65 and Stenotrophomonasmaltophilia MU 64. The essential oils were not effective against Candida albicans.

This study documents the in vitro antimicrobial activity of S. rupestris and S. amanica for the first time. The essential oils are shown to be effective against gram-positive bacteria, including multidrugresistant strains. These plants need to be studied on a larger scale to elucidate their mechanism of action and may be usefulas an alternative antimicrobial agent for multidrug resistant bacteria in the future.