Various medicinal plants are common in use in Nepal for the treatment of different diseases. Nowadays, drug resistance has emerged as a major problem for various infections, in such case plants can be used as alternative for the production of new antimicrobial agents. Thuja (in Nepali: dhupi) is a small evergreen genus of the Cupressaceae family. This species is widely cultivated as a common ornamental plant in Nepal and India. This study examined the antibacterial activity of Thuja leaves extract on gram positive (Staphylococcus aureus and Streptococcus spp.) and gram-negative bacteria (E. coli and Pseudomonas aeruginosa). Thuja leaves were collected from different localities of Dharan, and dried under shade for 10 days. They were then grinded using mechanical grinder. Leaf extract (oleoresin) was obtained by soxhlet extraction technique using mixture of Ethyl acetate, Ethanol and chloroform in the ratio 40:30:30 as the solvent. The antibacterial activity of Thuja oleoresin was tested using both Agar well diffusion as well as disc diffusion technique. Minimum Inhibitory Concentration(MIC) was determined by agar well diffusion on MHA plates. Thuja oleoresin showed distinct antibacterial activity towards all four isolates on both agar well and disc diffusion methods. MIC for Pseudomonas aeruginosa and Streptococcus spp. was found to be 12.5 µl whereas for E. coli and Staphylococcus aureus, MIC was 25 µl. Thus from our results, it is concluded that Thuja leaves have antibacterial effects and can be a potential source for production of antibacterial drugs.

Realizing an increasing need for a novel antibiotic, this study was carried out to screen antibacterial metabolites producing actinomycetes from 15 soil samples collected from Taplejung. Antibacterial metabolites producing actinomycetes were confirmed by primary screening and secondary screening. Macroscopic, microscopic, and biochemical characteristics were used for presumptive identification of probable actinomycetes genera. The potential isolate was cultured in starch casein broth for production of possible antibacterial compound. The antibacterial compound was extracted from fermented broth using organic solvents like ethyl acetate, n-butanol, chloroform, dichloromethane, and methanol. Among 24 isolates, only one (T18) showed antibacterial activity against both Gram-positive (Staphylococcus aureus and Bacillus subtilis) and Gram-negative (Escherichia coli, Salmonella Typhi and Pseudomonas aeruginosa) test-bacteria. The isolate was considered as Streptomyces spp based on microscopy and various biochemical, and physiological characteristics. Extracted antibacterial metabolite showed antibacterial activity with a MIC value of 1.2 mg/mL against E. coli (ATCC 25922). The chromatogram in Thin Layer Chromatography showed only one spot exhibited by extract with Rf value 0.87 suggested that the isolate produced a compound that was completely different from the spot with Rf value 0.94 produced by gentamicin (standard). This study revealed the distribution of the potent antibacterial metabolite producing actinomycetes in the soils of Taplejung.