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

A new naturally occurring polyketide, pseurotin A ₃ -10,11-acetonide (1), along with two known analogs, pseurotin A (2) and pseurotin A ₃ (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.