Abstract: Potassium diformate (KDF) is one of the representatives of acidifiers, which was approved for use as a feed additive by the European Union in 2001 and by China in 2005. Currently, there are more studies showing that KDF can improve the growth performance of animals. However, there are less researches to provide direct evidence of the prevention effect of KDF to infectious disease. The aim of this study was to evaluate the preventive effect of KDF on pathogenic bacteria in vitro and in vivo through bacterial inhibition assay and mouse infection model, and to detect the effect of KDF on intestinal flora of mice in order to investigate the mechanism of KDF action. First, detection of the minimum inhibitory concentration (MIC) of KDF against common pathogenic bacteria in the farm. Subsequently, C57/BL6 female mice aged 3-4 weeks and weighing 12-15 g were selected and examined for changes in body weight, tissue load, inflammatory cytokine levels and cecum pathology after infection with Salmonella Typhimurium in KDF treatment group (n=6) and control mice (n=6). The effects of feeding KDF on the cecum flora of mice were analyzed using 16S rRNA sequencing technology. The results showed that the MIC of KDF was 3.125 mg·mL^-1 for pathogenic bacteria such as Salmonella and Escherichia coli, and 6.25 mg·mL^-1 for bacteria such as Staphylococcus aureus and Pasteurella. In vivo, KDF pretreatment significantly reduced the bacterial loads in the blood and cecum (P<0.05), significantly reduced the levels of inflammatory cytokines IL-6, IL-12 and TNF-α in the blood (P<0.05), and alleviated the pathological changes in the cecum. Simultaneously, KDF significantly reduced the diversity of the intestinal flora of the cecum (P<0.01), which allowed the differential species presence. In addition, the species richness of the cecum flora of mice in the KDF treatment group decreased. At the phylum level, the relative abundance of the Proteobacteria was significantly higher in the KDF group (P<0.001). At the family level, the relative abundance of the Mogibacteriacceae was markedly lower in the KDF group (P<0.05). At the genus level, the relative abundance of the Akkermansia, Blautia, Lactobacillus and Eubacterium were increased. In summary, KDF showed significant inhibitory effects against common pathogenic bacteria in vitro, and prevents infection with the Salmonella in mice in vivo. The intestinal flora of mice changed significantly after KDF supplementation, and the increase in the abundance of beneficial genera such as Akkermansia, Blautia, Lactobacillus and Eubacterium may have a positive effect on the intestinal health of the animals.

Key words: potassium diformate, intestinal bacterial infection, prevention, Salmonella, intestinal flora