Screening of Antibiotic-Producing Actinomycetes from Marine, Brackish, and Terrestrial Sediments of Samal Island

Abstract

A total of 54 actinomycete isolates were obtained from terrestrial, brackish and marine sediment samples collected from Barangay San Isidro, Babak District, Samal Island. These were then tested for antagonistic activity against four test microorganisms: E. coli EC-7, S. aureus SA-12, C. utilis CU-14 and A. niger AN-20. Results indicated that 14 isolates were active against at least one of the test microorganisms, 13 of which were active against at least one test bacteria, and four against at least one test fungi. From these, it was noted that the terrestrial site was the richest source of antibiotic-producing actinomycetes wherein 52.17% of the terrestrial isolates were antibacterial and 13.04% were antifungal. No marine isolate was found active against the test microorganisms while one brackish isolate was found to be inhibitory. The upper 50% of the bioactive actinomycete isolates were further screened against other strains of the test microorganisms. Three out of the seven isolates exhibited antagonistic activity. Based on the mean diameter of inhibition zones, ti5 was chosen to be the most potent actinomycete isolate. It was subjected to the minimum inhibitory concentration assay, cultural characterization and morphological characterization. The minimum inhibitory concentration of ti5 was determined to be about 20% to 25%. Cultural and morphological characterization suggested that it belongs to the genus Micromonospora. The large number of actinomycetes with persistent antimicrobial activity qualifies Samal Island sediments as a potential source of novel antibiotics.