Antibacterial activity of an ethyl acetate extract from Streptomyces albus culture supernatant against Staphylococcus aureus
Abstract The increasing resistance of Staphylococcus aureus highlights the urgent need for new antibacterial alternatives. In this context, Streptomyces, a genus of actinobacteria widely recognized for its biosynthetic potential, represents a promising source of bioactive compounds. This study evaluated the antibacterial activity of a crude ethyl acetate extract obtained from the culture supernatant of Streptomyces albus against S. aureus strains. The extract was produced by submerged fermentation followed by liquid–liquid extraction with ethyl acetate. Antibacterial activity was assessed using the agar diffusion method, as well as by determining the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC). Two clinical strains (IC 3792 and IC 2141) and one reference strain (ATCC 29213) were evaluated. The extract produced inhibition zones ranging from 18.00 ± 1.0 mm to 22.33 ± 0.58 mm. MIC and MBC analyses demonstrated both inhibitory and bactericidal activity. Notably, strain IC 2141 exhibited an MIC of 625 µg/mL and a corresponding MBC, resulting in an MBC/MIC ratio ≤ 2, indicative of a bactericidal effect. These findings demonstrate that the crude extract obtained from S. albus exhibits antibacterial activity, including against strains with reduced susceptibility to conventional antibiotics. Overall, soil-derived actinobacteria represent a promising source of bioactive compounds, reinforcing the relevance of microbial bioprospecting in the development of new therapeutic strategies to address increasing bacterial resistance.