Immune Response to Hypervirulent Klebseilla pneumoniae Serotypes K1 And K2 In Animal Models

Background: HypervirulentKlebsiella pneumoniae (HvKp) is a globally emerging pathogen distinguished by severe clinical manifestations, including respiratory and systemic infections. Unlike classical K. pneumoniae (CKp),hvKp is associated with capsular serotypes K1 and K2, hypermucoviscosity, and enhanced virulence factors, posing significant public health risks. Understanding host immune responses tohvKp is critical for elucidating its pathogenicity. Aim: This study aimed to characterize the prevalence of K1/K2 serotypes in clinical isolates from humans and sheep, assess virulence phenotypes, and evaluate cytokine responses (IFN-γ and IL-10) ng/ml in rats infected with HvK pneumonia. Materials and Methods: A total of 300 samples (150 human sputum, 150 sheep nasal swabs) were collected. Isolates were identified using microbiological, biochemical (Vitek-2), and molecular methods (16S rRNA PCR). Hypermucoviscosity was confirmed via the string test. Capsular serotyping (K1/K2) was performed using magA and K2-specific PCR. Forty rats were divided into four groups: control (PBS) and infected (HvKp ATCC® 43816, 1×10⁸ CFU) via IN or SC routes. Serum IFN-γ and IL-10 ng/ml levels were measured post-infection. Results: Among 42 K. pneumoniae isolates (25 human17 sheep), 19.04% harbored K1/K2 serotypes. The string test identified of isolates as hypermucoviscous. Rats infected via the IN route exhibited significantly elevated IFN-γ levels (2.48 ± 0.47 ng/mL vs. control 0.50 ± 0.23 ng/mL, P