Intratracheal Aerosolization of Nocardia farcinica in Mice Optimizes Bacterial Distribution and Enhances Pathogenicity Compared to Intranasal Inoculation and Intratracheal Instillation

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Nocardia, an easily missed but potentially fatal opportunistic pathogen, can lead to serious infections like lung and brain abscesses. Intranasal inoculation (IN) is the traditional approach for constructing a Nocardia-induced pneumonia mice model, while it usually only results in limited local bacterial infection in the lungs. To comprehensively assess infection dynamics across distinct pulmonary inoculation routes in mice models, this study compared the pathogenicity of three different Nocardia farcinica pneumonia models established via IN, intratracheal aerosolization (ITA), and intratracheal instillation (ITI). C57BL/6J mice were infected with N. farcinica through IN, ITA and ITI with comparative analyses of bacterial distribution in lungs, survival rate, weight, bacterial load, inflammatory cytokines, histopathological characteristics and transcriptome differences. The findings suggest that ITA N. farcinica infections caused severer clinical symptoms, higher mortality, pulmonary bacterial load, levels of inflammatory cytokines in bronchoalveolar lavage fluid, and more significant histopathological damage to lungs than IN and ITI. Furthermore, ITA resulted in better lung bacterial distribution and delivery efficiency than ITI and IN. Transcriptome analysis of lungs from N. farcinica infected mice via IN, ITA and ITI revealed significant differential gene expression, whereas ITA route resulted in a larger fold change. ITA provides a more consistent and severe model of N. farcinica pneumonia in mice than IN and ITI, which can make the bacteria more evenly distributed in the lungs, leading to more severe pathological damage and higher mortality rates. In conclusion, ITA is an optimal route for developing animal models of N. farcinica pneumonia infections.

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