Chen Yu-jie;Wang Chun-jie;Hou Wen-qian;Wang Xiao-shuo;Gali Bing-ga;Huasai Si-mu-ji-de;Yang Si-qin;Wu A-qi-ma;Zhao Yu-fei;Wu Ying-ga;Chen Ao-ri-ge-le

Inner Mongolia Agr, Coll Vet Med, Hohhot 010018, Peoples R China;Inner Mongolia Agr Univ, Coll Anim Sci, Hohhot 010018, Peoples R China;Inner Mongolia Agr Univ, Vocat & Tech Coll, Baotou 014109, Peoples R China

antibacterial compound;Saccharomyces cerevisiae;Escherichia colt;hydrophobicity;permeation

The effects of antibacterial compounds produced by Saccharomyces cerevisiae in Koumiss on pathogenic Escherichia coli O-8 and its cell surface characteristics were investigated. S. cerevisiae isolated from Koumiss produced antibacterial compounds which were active against pathogenic E. coli O-8 as determined by the Oxford cup method. The aqueous phases from S. cerevisiae at pH=2.0 (S2) and pH=8.0 (S8) were extracted and tested, respectively. The organic acids of S2 and S8 were determined by high performance liquid chromatography (HPLC), and the concentrations of killer toxins were determined by enhanced bicinchoninic acid (BCA) Protein Assay Kit. The minimum inhibition concentration (MIC) and the minimum bactericidal concentration (MBC) of S2 and S8 on E. coli O-8 were determined by the broth microdilution method. The effects of S2 and S8 on the growth curve of E. coli O-8 were determined by turbidimetry, and the hydrophobicities of E. coli O-8 cell surface were determined using the microbial adhesion to solvents method, the permeation of E. coli O-8 cell membrane were determined by the o-nitrophenyl-beta-D-galactoside (ONPG) method. Aqueous phases at pH 2.0 and 8.0 had larger inhibition zones and then S2 and S8 were obtained by freeze-drying. The main component in S2 was citric acid and it was propanoic acid in S8. Other organic acids and killer toxins were also present. Both the MICs of S2 and S8 on E. coli O-8 were 0.025 g mL(-1), the MBCs were 0.100 and 0.200 g mL(-1), respectively. The normal growth curve of E. coli O-8 was S-shaped, however, it changed after addition of S2 and S8. E. coli O-8 was the basic character, and had a relatively hydrophilic surface. The hydrophobicity of E. coli O-8 cell surface and the permeation of E. coli O-8 cell membrane were increased after adding S2 and S8. The present study showed that S2 and S8 inhibit the growth of pathogenic E. coli O-8 and influence its cell surface characteristics.