Isolation, characterization, and screening of actinomycetes producing bioactive compounds from Egyptian soil

Abstract

Background Unsuitable prescription and the inappropriate use of antibiotics have led to the development of antibiotic resistance in many pathogenic bacteria. So, there is a need to screen for alternative sources, such as actinomycetes, a potent antibiotic producer for antimicrobial activity, with the hope of discovering novel strains proficient to produce antibiotics against the resistant bacteria. Materials and methods In the current work, six actinomycetes were isolated from Egyptian soil, characterized, and then identified by microscopic and macroscopic observations. The bioactive substances were extracted by the solvent extraction method using ethyl acetate. Antimicrobial activity of the obtained extracts was evaluated against some gram-positive and gram-negative bacteria. Fourier-transform infrared spectroscopy analysis and cytotoxic activity of the most active extracts were carried out. Results and conclusion Crude extract of A2 showed 30±0.10-mm mean inhibition zones against gram-positive bacteria Bacillus megaterium. Significantly, the isolate A6 showed the highest mean zone of inhibition of 20.0±0.1, 19.4±0.05, and 19.0±0.10 mm against Pseudomonas aeruginosa, Klebsiella oxytoca, and Escherichia coli, respectively. The isolate A5 only showed the largest antibacterial activity against B. megaterium, with inhibition zone of 69±0.28 mm. Only two isolates (A2 and A6) were chosen for further study based on broad-spectrum activity in comparison with other isolates. The two isolates A2 and A6 were identified as Streptomyces enissocaesilis MT658130 and Streptomyces atrovirens MT658195, respectively, using 16S rRNA. Fourier-transform infrared analysis of the extract of two strains reported the existence of OH, C=C, C-O, S=O, N=C=S, and C-Br as the most efficient groups. Cytotoxic activity of S. enissocaesilis A2 and S. atrovirens A6 extracts against hepatocellular carcinoma (HepG2) cell line showed good cytotoxicity, with 2.97 and 1.48 µg/ml IC50 value, respectively. The results evoked that actinomycete isolates under study have potent biological activities.