Immunological and histopathological effects of hypervirulent Klebsiella pneumoniae in a rat model of respiratory infection | ||
| Microbes and Infectious Diseases | ||
| Articles in Press, Accepted Manuscript, Available Online from 27 September 2025 | ||
| Document Type: Original Article | ||
| DOI: 10.21608/mid.2025.398646.2959 | ||
| Authors | ||
| Ali A. kadhum* ; Hanaa K. Ibraheim; Mohammed H. Khudor | ||
| Department of Microbiology, College of Veterinary Medicine, University of Basrah, Iraq | ||
| Abstract | ||
| Background: Klebsiella pneumoniae is a significant cause of respiratory infections and is associated with high morbidity and mortality rates. Hypervirulent strains (hvKp) pose an increased threat to immunocompromised individuals; however, their specific immunological and pathological impacts remain inadequately characterized. Aim: The study aimed to determine the effects of Hv. Klebsiella pneumoniae on some immune indicators, such as TNF-α and IL-12, and to study the pathology that occurs in infected rats. Methods: Three hundred respiratory samples (150 human sputum and 150 sheep nasal swabs) were collected from clinical settings. Samples were cultured on MacConkey agar, and Klebsiella pneumoniae isolates were identified by Gram staining, VITEK-2, biochemical tests, and 16S rRNA PCR. Hypervirulent strains (hvKp) were confirmed by a positive string test (mucoviscosity ≥5 mm). Forty adult male albino rats were acclimatized for 14 days and divided into four groups: (1) PBS subcutaneously (SC), (2) PBS intranasally (IN), (3) hvKp (1×10⁸ CFU/mL) SC, and (4) hvKp IN. Post-infection, serum TNF-α and IL-12 levels were quantified by ELISA, while lung and spleen tissues were subjected to histopathological examination after H&E staining. Results: Among the 42 confirmed K. pneumoniae isolates (25 humans, 17 sheep), 19% (8/42) were hypervirulent (five humans, three sheep), exhibiting ≥5 mm string formation. Infected rats showed significantly elevated IL-12 levels (IN: 481.4 ± 36.1 pg/mL; SC: 432.1 ± 12.3 pg/mL) versus controls (IN: 334.8 ± 18.6; SC: 295.6 ± 14.2; p<0.01), and increased TNF-α (Infected-IN: 1.86 ± 0.36 pg/mL; Infected-SC: 1.52 ± 0.45 pg/mL vs. controls; p<0.05). Histopathological examination revealed severe lung damage in the infected groups, including alveolar destruction, bronchial narrowing, neutrophilic infiltration, and vascular congestion. Spleens displayed lymphoid follicle hyperplasia, white pulp expansion, and red pulp hyperemia, confirming immune organ involvement. Conclusion: Increased levels of cytokines TNF-α and IL-12 in rats infected with Hv. Klebsiella pneumniae as well as the occurrence of clear tissue changes in the infected lung, destruction of alveolar sacs and interstitial tissues within the lung, and secretions within the alveoli. The spleens of rats injected with bacteria had immune effects, represented by the appearance of white pulp, irregularity, and enlargement of the lymph follicles. | ||
| Keywords | ||
| Hypervirulent Klebsiella pneumoniae; TNF-α; IL-12; Lung pathology; Rat model | ||
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