Sequential development of pathology and pathogenesis of capsular serotype D of Pasteurella multocida of porcine origin in mouse model

To understand the mechanism of host-pathogen interaction during the progression of Pasteurella multocida capsular serotype D of porcine origin causing pneumonia/septicemia, 36 adult Swiss albino mice were intranasally inoculated with 25 μl of P. multocida serotype D@10⁹ CFU/ml and sacrificed at 6, 12, 24, 48, 72 and 96 hours post inoculation. The infected mice showed varied clinical signs of depression, ruffled fur, ocular discharge, watery to mucoid nasal discharge with labored breathing pronounced during 24-48 HPI and declined thereafter. The leucocytosis, anaemia, low PCV, progressive neutrophilia with lymphocytopenia changes in these infected groups of mice paralleled with the clinical signs. The serum biochemical parameters such as total protein, blood urea nitrogen, creatinine, glucose, SGOT, SGPT and C-reactive protein were significantly increased. The higher level of LPO, lower level of antioxidant enzymes (CAT, SOD and GSH) and higher values of proinflammatory cytokine genes (TNF-α, IL-1β and IL-6) in lungs and spleen of the inoculated mice as compared to control mice suggest towards the establishment of pneumonia and sep-ticemia. The lesions of bronchopneumonia, splenitis, nephritis, hepatitis, enteritis and myocarditis along with the demonstration of bacterial antigens in lungs and spleen well correlated with severity of histopathological lesions at different time points. Apoptotic nuclei were detected in infiltrating leukocytes of the lungs and splenocytes on TUNEL staining. The inflammatory lesions as well as the apoptosis were highest during 24-48 HPI followed by gradual decrease till the end of the experiment. This is the first report on elucidating the pathogenesis of P. multocida capsular serotype D of porcine origin.