ANTIBACTERIAL ACTIVITY OF THE METABOLIC BY-PRODUCTS OF A VEILLONELLA SPECIES AND BACTEROIDES-FRAGILIS

A Veillonella species and Bacteroides fragilis were isolated from the cecal contents of adult chickens. When growth on an agar medium supple mented with 0.4% glucose and adjusted to pH 6.5, mixed cultures contai ning Veillonella and B. fragilis inhibited the growth of Salmonella ty phimurium, Salmonella enteritidis, Escherichia coli 0157:H7 and Pseudo monas aeruginosa. Decreasing the glucose concentration of the agar dec reased the inhibitory activity of the mixed culture. Mixed cultures gr own on agar media supplemented with 0.5% glucose and adjusted to pH 6. 5, 7.0 or 7.5 also inhibited the growth of S. typhimurium, S. enteriti dis, E. coli 0157:H7 and P. aeruginosa: However, increasing the pH of the agar decreased the inhibitory activity of the mixed culture. Pure cultures of Veillonella or B. fragilis did not inhibit the growth of S . typhimurium, S. enteritidis, E. coil 0157:H7 or P. aeruginosa on any of the agar supplemented with different concentrations of glucose or on any of the agar adjusted to different pH levels. The inhibitory act ivity of the mixed culture was correlated with the concentration of vo latile fatty acids that were formed as B. fragilis metabolized glucose to produce succinate and acetate and as the succinate produced by B, fragilis was decarboxylated by Veillonella to produce propionate.