<scp> <i>Enterococcus faecium B13</i> </scp> Affects Mice Growth by Regulating Gut Microbiota and Metabolites

Gut microbiota can influence the growth performance of animals. In our previous study, <i>Enterococcus faecium B13</i> exhibited promoting growth in piglets. This study aimed to reveal the mechanism underlying the growth promotion. Therefore, B13 was administered to male mice via oral gavage, and the growth performance, gut microbiota, and metabolites were analyzed. Results showed that the weight gain trend in the B13 group was slightly higher than in the control group during 28 days, and the serum triglycerides (TG) level was significantly lower in the B13 group (<i>p</i> < 0.05). Notably, the microbial composition differed between the two groups. The ratio of <i>Firmicutes/Bacteroidetes</i> (F/B) rose in the colon. The <i>Allobaculum</i> and <i>Alloprevotella,</i> which promoted growth and inhibited obesity, were significantly different genera in the ileum and colon, separately. On the 11th day after B13 withdrawal, all differential genera, except for <i>Alloprevotella</i> and <i>RF39</i>, returned to normal levels. A total of 53 differential metabolites were identified by Liquid Chromatograph Mass Spectrometer (LC-MS), with the most significantly altered substances mainly involved in the arachidonic acid metabolic pathway, arginine and ornithine metabolic pathway, arginine and proline metabolic pathway and linoleic acid metabolic pathway. Additionally, Spearman's correlation analysis indicated a significant correlation between the <i>Alloprevotella</i> and the main differential metabolites. All these results suggest that <i>Alloprevotella</i> might play a major role under the conditions of this experiment. This study revealed the possible growth-promoting mechanism of B13 and suggests its potential as a probiotic.