Histopathological changes of Quercetin on internal organs against Klebsiella pneumoniae in Mice

Background: Quercetin is a natural flavonoid present in fruits and medicinal herbs with antioxidant, anti-inflammatory, and antimicrobial properties. It modulates immune responses and protects tissues from oxidative and infectious insults. Klebsiella pneumoniae is a Gram-negative bacterium and a significant cause of pneumonia and septicemia, and its increasing resistance requires effective natural adjunctive treatments. Aims: The current study evaluated the histopathological impact of quercetin on internal organs in mice experimentally infected with K. pneumoniae. Forty Swiss mice were divided into groups treated with quercetin at 150, 100, and 50 mg/ml once weekly for six weeks, and a control group received PBS. All animals were challenged intraperitoneally with K. pneumoniae (1.5×10⁸ CFU/ml). Seven days later, spleen, liver, lung, and intestine were collected, fixed in 10% formalin, and histologically examined. Results: Pre-challenge quercetin-treated groups showed lymphoid hyperplasia and megakaryocytic activation in the spleen, indicating immune stimulation. Treated mice after infection had reduced splenic hypoplasia, hepatic mild degeneration instead of diffuse necrosis, and preserved alveolar and intestinal architecture. Intestinal villi were truncated but with preserved mucosal integrity and reduced lymphocytic infiltration compared to infected controls. Conclusion: Quercetin exhibited a biphasic immunomodulatory and tissue-protective effect—pre-infection stimulation of immune readiness and post-infection attenuation of inflammation and necrosis. These findings sanction its antioxidant and anti-inflammatory roles and suggest