[Protective effect and mechanism of Bifidobacterium bifidum TMC3115 on long-term colitis in mice which exposed to antibiotic in early life]

Objective: To explore the protective effect and mechanism of Bifidobacterium bifidum TMC3115 of improving the gut microbiota disorder caused by antibiotic exposurein early life, and the possible protection of inflammatory bowel disease in adulthood in mice.

Methods: 80 newborn mice were randomly divided into 3 groups, a blank control group(n=40), a ceftriaxone exposure group(n=20), a Bifidobacterium bifidum TMC3115 intervention group(n=20). After birth, they were respectively treated with saline, ceftriaxone(100 mg/kg), and ceftriaxone(100 mg/kg) + TMC3115(1×10~9CFU/d) for 3 weeks. After 3 weeks, half of each group was randomly sacrificed, and the rest were normally fed to 6 weeks. At 6 weeks, the blank control group was randomly divided into a negative control group(n=10) and a colitis model group(n=10). The negative control group drunk pure water freely, and the other three groups were added 3% DSS to the drinking water for 4 days to induce colitis. At 6 weeks and 4 days, the remaining mice were sacrificed. The weight change, spleen coefficient, gut microbiota analysis based on second-generation sequencing and serum tumor necrosis factor-α(TNF-α), interleukin-6(IL-6), and interleukin-10(IL-10)levels of the mice at 3 weeks and after DSS intervention were recorded. In addition, the colon length and inflammation pathology score of the mice after DSS intervention were also measured.

Results: At 3 weeks, compared with the control, antibiotic exposure in the early life inhibited the weight gain and reduced the diversity and uniformity of the gut microbiota of the mice(P<0.05). The intervention of TMC3115 under antibiotic exposure during this period increased the relative abundance of Bifidobacterium in the intestines(P<0.05), and the effect still existed after DSS stimulation in adulthood, laying the foundation for TMC3115 to exert long-term benefits. After DSS stimulation in adulthood, mice showed significant weight gain inhibition, colon length shorteningand inflammation pathology scoreincrease compared with the negative control(P<0.05), showed the inflammatory bowel disease(IBD)model was successfully constructed. The relative abundance of beneficial bacteria such as Lactobacillus in the Bifidobacterium bifidum TMC3115 intervention group increased compared with the ceftriaxone exposure group(P<0.05), while the relative abundance of harmful bacteria such as Staphylococcus, Clostridium, and Desulfovibrio decreased(P<0.05). Furthermore, the mice exposed to antibiotic in early life produced a stronger immune response, but the mice which received TMC3115 intervention at the same time had a significant decrease in serum TNF-α and IL-6 levels and increase in IL-10 level compared with the mice which only interfered with antibiotics(P<0.05).

Conclusion: Antibiotic exposure in early life is a negative factor for long-term inflammatory bowel disease, and TMC3115 has preventive significance for long-term inflammatory bowel disease under the background of antibiotic exposure. The mechanism of TMC3115 may be to adjust the gut microbiota and balance the immune system.