Biosurfactins production by Bacillus amyloliquefaciens R3 and their antibacterial activity against multi-drug resistant pathogenic E. coli.

In this work, the anti-Escherichia coli activity of the bioactive substances produced by Bacillus amyloliquefaciens R3 was examined. A new and cheap medium for production of the anti-E. coli substances which contained 20.0 g L(-1) soybean powder, 20.0 g L(-1) wheat flour, pH 6.0 was developed. A crude surfactant concentration of 0.48 mg mL(-1) was obtained after 27 h of 10-L fermentation, and the diameter of the clear zone on the plate seeded with the pathogenic E. coli 2# was 23.3 mm. A preliminary characterization suggested that the anti-E. coli substances produced by B. amyloliquefaciens R3 were the biosurfactins (F1, F2, F3, F4, and F5) with amino acids (GLLVDLL) and hydroxy fatty acids (of 12-15 carbons in length). It was found that all the strains of the pathogenic E. coli showed resistance to several different antibiotics, suggesting that they were the multi-drug resistance and all the strains of the pathogenic E. coli were sensitive to the biosurfactins, indicating that the biosurfactins produced by B. amyloliquefaciens R3 had a broad spectrum of antibacterial activity against the pathogenic E. coli with multi-drug resistant profiles. After the treatment with the purified biosurfactin (F1), the cell membrane of both the whole cells and protoplasts of the E. coli 2# was damaged and the whole cells of the bacterium were broken.