Antibacterial activity of selected orchid species of Nepal

Abstract

Orchidaceae, a highly advanced and widely spread family of monocotyledonous plants. Orchids have been found to contain a rich source of natural compounds with significant therapeutic activities against various disease. So this study mainly focused on antibacterial activity to generate natural medicines to substitute synthetic drugs. The orchid plants were collected from various regions of Nepal and subsequent extract preparation and laboratory work conducted at the Annapurna Research Center. A total of fifteen orchid species were selected for the purpose of this study. The different parts of orchids were used for extraction using methanol through a combination of the Percolation and intermittent sonication methods. After that in vitro antibacterial evaluation was conducted using the agar well diffusion technique with different concentration. Out of 15 species, the highest yield was obtained from Habenaria marginata 15%, and the lowest was from Coelogyne stricta 1%. In the qualitative analysis, various reagents were used to quantify tannins, flavonoids, glycosides, phenols and alkaloids. A qualitative phytochemical screening indicate that alkaloids and flavonoids were present in the extracts of all the orchid species that were tested. Both Phenol and Carbohydrate were absence in Coelogyne stricta and Eria graminifolia. The antibacterial activity of the methanol extracts from these plants was evaluated against medically significant bacteria. Enterococcus faecalis, Acinetobacter baumannii, Escherichia coli and Shigella sonnei were Gram negative whereas Staphylococcus aureus was Gram positive bacteria. All 15 plants showed activity against at least one bacterium. The two orchid plants, Coelogyne stricta and Otochilus albus, exhibited broad-spectrum activity by showing a high zone of inhibition against all tested bacteria with zone of inhibition (20mm) and (21mm) against Acinobacter baumannii respectively. Similarly, The MIC values for the tested orchid extracts range from 1.25 mg/ml to 2.5 mg/ml, while the MBC values range from 0.3125 mg/ml to 0.625 mg/ml. So Otochilus albus exhibits strong antibacterial properties against Acinobacter baumannii species, and its corresponding MIC and MBC values provide further evidence of its antibacterial effectiveness. Therefore, it is worthy to conduct additional investigations into this specific species to reveal its potential benefits. Furthermore, there is scope for conducting additional laboratory experiments and research work to develop new pharmaceutical products.

Keywords: Orchids, Phytochemical compounds, Antibacterial activity, MBC, MIC