Effects of thymol on ruminal microorganisms

Thymol (5-methyl-2-isopropylphenol) is a phenolic compound that is used to inhibit oral bacteria. Because little is known regarding the effects of thi s compound on ruminal microorganisms, the objective of this study was to de termine the effects of thymol on growth and lactate production by the rumin al bacteria Streptococcus bovis JB1 and Selenomonas ruminantium HD4. In add ition, the effect of thymol on the in vitro fermentation of glucose by mixe d ruminal microorganisms was investigated. Neither 45 nor 90 mug/ml of thym ol had any significant effect on growth or lactate production by S. bovis J B1, but 180 mug/ml of thymol completely inhibited growth and lactate produc tion. In the case of S. ruminantium HD4, 45 mug/ml of thymol had little eff ect on growth and lactate production; however, 90 mug/ml of thymol complete ly inhibited growth of S, ruminantium HD4. Thymol also decreased glucose up take by whole cells of both bacteria. When mixed ruminal microorganisms wer e incubated in medium that contained glucose, 400 mug/ml of thymol increase d final pH and the acetate to propionate ratio and decreased concentrations of methane, acetate, propionate, and lactate. Ln conclusion, thymol was a potent inhibitor of glucose fermentation by S. bovis JB1 and S. ruminantium HD4. Even though thymol treatment decreased methane and lactate concentrat ions and increased final pH in mixed ruminal microorganism fermentations of glucose, concentrations of acetate and propionate were also reduced.