Abstract: Objective: To study the laxative effect of Lactiplantibacillus plantarum P9 on functional constipation in mice and its effect on the gut microbiota. Methods: One hundred Balb/c male mice were randomly divided into five groups of 20 mice each: blank, model, low-dose P9 (dried bacterial powder with a viable cell count of 2.0 × 1011 CFU/g, 0.42 mg/(kg mb·d)), medium-dose P9 (0.84 mg/(kg mb·d)), and high-dose P9 (2.5 mg/(kg mb·d)). The mice in the three dose groups were gavaged with L. plantarum P9 suspension in sterile deionized water at 10 mL/(kg mb·d) for 15 days, while those in the blank and model groups were gavaged with an equal volume of distilled water. On day 16 of the experiment, loperamide at 4 mg/(kg mb·d) was applied by gavage to induce functional constipation in mice. Ten mice with constipation were randomly selected for defecation test, where the time of the first black stool and the weight of black stool at 6 h were measured. The remaining 10 mice were measured for the rate of ink advancement, and the composition of the cecal flora was determined by 16S rRNA high-throughput sequencing. After the end of the defecation test, the remaining mice in the model and P9 intervention groups were continuously gavaged with loperamide at 4 mg/(kg mb·d) to establish a mouse model of functional constipation, while those in the blank group was given an equal volume of distilled water. The mice in the P9 intervention groups were administered with L. plantarum P9 at 1 h after modeling, whereas those in the blank and model groups were given an equal volume of distilled water by gavage for six days. The histopathological changes of the colon were observed by hematoxylin-eosin (HE) staining, and serum motilin (MTL), gastrin (GAS), acetylcholine (AchE), and nitric oxide (NO) levels were determined. Results: Compared with the model group, the medium dose of L. plantarum P9 significantly shortened the time the first black stool in mice with functional constipation (P < 0.05), and the medium and high doses of L. plantarum P9 significantly increased the volume of black stool excretion at 6 h (P < 0.01 and P < 0.001). The low, medium and high doses of L. plantarum P9 significantly increased the rate of ink advancement in mice (P < 0.01, P < 0.05, and P < 0.001), and augmented the serum levels of MTL, GAS and AchE. The low dose of L. plantarum P9 significantly increased the level of GAS (P < 0.001), the high dose of L. plantarum P9 significantly increased the level of MTL (P < 0.01), the low and medium doses of L. plantarum P9 significantly increased the level of AchE (P < 0.05), and the low and medium doses of L. plantarum P9 significantly decreased the level of NO (P < 0.05). The damaged intestinal barrier was repaired and the richness and diversity of the gut microbiota were significantly increased at all doses of L. plantarum P9. Conclusion: L. plantarum P9 has a good laxative effect, and its mechanism may be related to improving intestinal motility, regulating gastrointestinal serum neurotransmitters and increasing the richness and diversity of the gut microbiota.

Key words: Lactiplantibacillus plantarum P9; functional constipation; laxative effect; gut microbiota; 16S rRNA