Vitamin D Improves Klebsiella-Induced Severe Pneumonia in Rats by Regulating Intestinal Microbiota

Background: In the context of progressively uncontrolled drug resistance of bacteria, the difficulty of treating Klebsiella (KP)- induced pneumonia increases. Searching for drugs other than antibiotics has become an urgent task. Vitamin D (VD), meanwhile, is shown to be capable of treating pneumonia. Therefore, we aimed to explore the effects and mechanisms of VD on KP-infected rats. Methods: Male Sprague Dawley rats were divided into the Control, VD, KP and KP+VD groups. A rat pneumonia model was induced using an intratracheal drop of 2.4x108 CFU/mL KP. VD treatment was performed by gavage using 5 mu g/kg. Subsequently, the survival of the rats was recorded, and the lungs, bronchoalveolar lavage fluid, and feces of the rats were collected 4 days after KP infection. Next, the water content of lung tissues was measured by the wet-to-dry weight ratio. Histopathological changes of lung tissues were observed by Hematoxylin and Eosin staining and the levels of inflammatory factors (TNF-alpha, IL-1 beta, MCP1) were detected using ELISA. The feces of rats in each group were also subjected to 16S rDNA gene analysis of intestinal microbiota. Results: Compared with the KP group, the KP+VD group showed a significant increase in survival, a significant decrease in water content and bacterial counts in the lungs, a significant improvement in lung injury, and a significant decline in the levels of TNF-alpha, IL- 1 beta, and MCP1. According to the 16S rDNA sequencing, VD altered the structure of the intestinal bacterial community in the KP- infected rats and made the species richness similar to that of healthy rats. Additionally, the abundance of Anaeroglobus was significantly increased in the KP+VD group. Conclusion: VD modulates intestinal microbiota to increase the resistance of rats to pneumonia caused by Klebsiella infection.