Protective Effect of Escherichia coli Nissle 1917 on Salmonella typhimurium Infection by Regulating Intestinal Flora

Salmonellosis is a global foodborne pathogen with zoonotic importance that seriously threatens livestock breeding and human health. Due to the implementation of an anti-resistance policy, probiotics as an alternative to antibiotics have attracted widespread attention. In this study, the widely used probiotic Escherichia coli Nissle 1917 (EcN) was selected to study its protective effect on mice infected with Salmonella typhimurium. Two mice groups (n = 15) were treated with either EcN and PBS. Flow cytometry showed that the frequency of mature dendritic cells in the Peyer's patch was significantly increased compared to the PBS group. Previous administration of EcN protected against challenge with Salmonella typhimurium infection as an increased survival rate of the mice, a decreased degree of pathological changes, and the number of live bacteria in the spleen and liver were recorded compared to the control group. The results of 16S rRNA high-throughput sequencing of fecal microbial flora showed that EcN could reduce the abundance of microorganisms in the intestine and reduce the proportion of Lactobacillus, while Ruminococcaceae sp., Rikenella sp. and Bifidobacterium sp. disappeared. In contrast, the abundance of Bacteroides increased, which reduced the effect of Salmonella typhimurium on the distribution of intestinal microorganisms. Our results demonstrated that EcN has a protective effect against Salmonella typhimurium infection and may act as a candidate probiotic bacterium to apply in the future.