In-vitro Anti-food Poisoning Bacteria and Cytotoxic Activities of Bioactive Compounds Produced by Streptomyces sp. A10 Isolated from Fermented Food

Streptomyces sp. A10 was isolated from fermented food, PLA-SOM, collected from Nakhon Si Thammarat province, Thailand and identified by means of MALDI Biotyper, designated as Streptomyces violaceoruber. It could produce bioactive compounds (BCs) that showed spectrum of antibacterial activity against representative of Gram-positive bacteria (Staphylococcus aureus TISTR 517 and Bacillus cereus ATCC 11778) and Gram-negative bacteria (Pseudomonas aeruginosa TISTR 1467 and Salmonella typhimurium TISTR 292) by using cross streak method. Moreover, it could excrete the BCs into medium broth (half-formula of Luria Bertani) within 4 days of incubation period at 30 °C in shaking incubator 200 rounds per minute (RPM). The excreted BCs from cell-free supernatant (CFS) was determined the protein concentration by means of Bradford assay and investigated the antibacterial activity and cytotoxicity against brine shrimp nauplii by using broth microdilution method and brine shrimp lethality bioassay, respectively. Moreover, cell cytotoxicity activity of CFS was also investigated using MTT assay in HepG2 cells. The results demonstrated that the BCs which had protein concentration equal to 254 µg protein/ml showed strong activity against representative of Gram-positive bacteria, moderate activity against representative of Gram-negative bacteria, but Ps. aeruginosa TISTR 1467 is resist to these BCs. The MIC, MBC and LC50 of BCs were in the range of 0.49 - 63.50, 0.49 - 127.00, and 131.58 µg protein/ml, respectively. Moreover, CFS (10-80%) had no cytotoxic effect on HepG2 cells. It implied that BCs may contain the important polypeptide substances that can be used as model for development of novel polypeptide antibiotic or food preservative agents.