The Prophylactic Protection of Salmonella Typhimurium Infection by Lentilactobacillus buchneri GX0328-6 in Mice

Abstract

Salmonellosis is a disease caused by non-typhoid Salmonella, and although some lactic acid bacteria strains have been shown previously to relieve Salmonellosis symptoms, little has been studied about the preventive mechanism of Lentilactobacillus buchneri (L. buchneri) against Salmonella infection in vivo. Therefore, the L. buchneri was fed to C57BL/6 mice for 10 days to build a protective system of mice to study its prevention and possible mechanisms. The results showed that L. buchneri GX0328-6 alleviated symptoms caused by Salmonella typhimurium infection among C57BL/6 mice, including low survival rate, weight loss, increase in immune organ index and hepatosplenomegaly, and modulated serum immunoglobulin levels and intrinsic immunity. Importantly, the L. buchneri GX0328-6 enhanced the mucosal barrier of the mouse jejunum by upregulating the expression of tight junction proteins such as ZO-1, occludins, and claudins-4 and improved absorptive capacity by increasing the length of mouse jejunal villus and the ratio of villus length to crypt depth and decreasing the crypt depth. L. buchneri GX0328-6 reduced the intestinal proliferation and invasion of Salmonella typhimurium by modulating the expression of antimicrobial peptides in the intestinal tract of mice, and reduced intestinal inflammation and systemic spread in mice by downregulating the expression of IL-6 and promoting the expression of IL-10. Furthermore, L. buchneri GX0328-6 increased the relative abundance of beneficial bacteria colonies and decreased the relative abundance of harmful bacteria in the cecum microflora by modulating the microflora in the cecum contents.

Keywords: Lentilactobacillus buchneri; Salmonella typhimurium; Gene expression; Gut microbiota.

Fig. 1

The body weight change (a), survival rate (b), and immune organ index (c) in mice treated or not during 10 days by L. buchneri GX0328-6 and then infected or not with Salmonella typhimurium SM022. The negative control group (CON) and L. buchneri group (LB) were only fed with saline and L. buchneri GX0328-6 respectively for 10 consecutive days; the prophylactic group (LB + SM022) and the positive group (SM022) were given L. buchneri GX0328-6 and saline respectively for 10 consecutive days, and then the mice were fed with Salmonella typhimurium SM022. *P < 0.05, ns had no statistical significance. (one-way ANOVA)

Fig. 2

The levels of immunoglobulin IgG (a), IgM (b), and IgA (c) in mice treated or not during 10 days by L. buchneri GX0328-6 and then infected or not with Salmonella typhimurium SM022, the contents of Salmonella typhimurium in mouse liver (d), spleen (e) and cecum (f) tissues in mice treated or not during 10 days by L. buchneri GX0328-6 and then infected with Salmonella typhimurium SM022 (n = 10) *P < 0.05, **P < 0.01, ****P < 0.0001, ns had no statistical significance (one-way ANOVA)

Fig. 3

The representative liver micrograph of mice treated or not during 10 days by L. buchneri GX0328-6 and then infected with Salmonella typhimurium SM022. The black thin arrow indicates that there are inflammatory cells (10 ×); the red thick arrow indicates necrosis of liver cells (40 ×); the black triangle box indicates the aggregation of red blood cells (40 ×). b is the result of liver inflammation–related cell frequency. ***P < 0.001 (one-way ANOVA)

Fig. 4

The pathological changes (a) of jejunum mucosa in mice, the villus length (b), the crypt depth (c) and the ratio (d) of villus and crypt depth in the jejunum of mice treated or not during 10 days by L. buchneri GX0328-6 and then infected with Salmonella typhimurium SM022. **P < 0.01; ***P < 0.001 (one-way ANOVA)

Fig. 5

mRNA relative expression amounts of inflammation-related cytokines IL-6 (a) and IL-10 (b) and antibacterial peptides Ang4 (c) and REGIII (d) in the jejunum of mice treated or not during 10 days by L. buchneri GX0328-6 and then infected or not with Salmonella typhimurium SM022. (n = 6) *P < 0.05, **P < 0.01, ***P < 0.001 (one-way ANOVA)

Fig. 6

mRNA relative expressions of tight junction proteins (ZO-1, occludins, claudin-4) in the jejunum of mice treated or not during 10 days by L. buchneri GX0328-6 and then infected or not with Salmonella typhimurium SM022. (n = 6) *P < 0.05, **P < 0.01, ***P < 0.001 (one-way ANOVA)

Fig. 7

Effect of L. buchneri GX0328-6 on cecal microbiota of mice infected with Salmonella typhimurium at phyla level (n = 3)

Fig. 8

Effect of L. buchneri GX0328-6 on cecal microbiota of mice infected with Salmonella typhimurium at genus level (n = 3)

Fig. 9

Comparison of relative abundance of significantly different microbial groups at the level of phyla (a, b) and genus (c, d). Mann–Whitney U test was used for statistical analysis, and the error-free rate (FDR) was corrected. It was compared with DFE + PBS mice (n = 3) *P < 0.05 (one-way ANOVA)