Polyketides from a soil -derived Streptomyces sp. CSDX076 and their antimicrobial activities

A new naturally occurring polyketide, pseurotin A3-10,11-acetonide (1), along with two known analogs, pseurotin A (2) and pseurotin A3 (3), was isolated from the culture broth of Streptomyces sp. CSDX076. The structures of these compounds were determined by extensive 1D and 2D nuclear magnetic resonance (NMR), ultraviolet (UV), and high-resolution electrospray ionization mass spectrometry (HRESIMS) spectroscopic analyses. All isolated compounds (1-3) were evaluated for antimicrobial activity against a panel of seven pathogenic strains using disc diffusion and broth microdilution methods. Notably, compound 1 exhibited moderate activity against Brucella melitensis with a minimum inhibitory concentration (MIC) of 8.0 μg/mL, while compound 2 showed weak activity against Staphylococcus epidermidis (MIC = 128.0 μg/mL); compound 3 was inactive against all tested strains. This study reports, for the first time, the antibacterial effects of these compounds against the respective pathogens.