Abstract: In this study, we isolated and identified lactic acid bacterial (LAB) strains from the gut of healthy elderly people in Xiangyang and Enshi, Hubei and then selected Lactobacillus fermentum strains for analysis by multilocus sequence typing (MLST). Results showed that by cultivable methods, 15 species of LAB were obtained belonging to five genera with Lactobacillus being the single dominant genus. In general, L. fermentum and L. salivarius account for about 55% of the total intestinal LAB strains, indicating that the human intestine can be an important source of L. fermentum. MLST analysis based on eight housekeeping genes showed that 25 L. fermentum strains originating from the elderly gut could be divided into 25 sequence types (ST), indicating high genetic diversity. Selection pressure analysis and phi-test showed that the eight housekeeping genes were purified and selected, and among these only the gene rpoB experienced recombination events. In addition, the evolutionary analysis based on Prim’s algorithm and global optimal BURST (goeBURST) algorithm showed that nearly half of the intestinal L. fermentum strains had the tendency to form one single branch, indicating that they had host specificity. This may be due to adaption to the intestinal environment. These strains were likely to undergo an evolutionary process different from that in fermented food habitat in order to adapt to the intestinal environment.

Key words: elderly gut; lactic acid bacteria; multilocus sequence typing; Lactobacillus fermentum; house-keeping genes