Sensitive bioluminescence imaging of fungal dissemination to the brain in mouse models of cryptococcosis

Abstract

Cryptococcus neoformans is a leading cause of fungal brain infections, but the mechanism of dissemination and dynamics of cerebral infection following pulmonary disease are poorly understood. To address these questions, non-invasive techniques that can study the dynamic processes of disease development and progression in living animal models or patients are required. As such, bioluminescence imaging (BLI) has emerged as a powerful tool to evaluate the spatial and temporal distribution of infection in living animals. We aimed at studying the time profile of the dissemination of cryptococcosis from the lung to the brain in murine models by engineering the first bioluminescent C. neoformans KN99α strain expressing a sequence-optimized red-shifted luciferase. The high pathogen-specificity and sensitivity of BLI was complemented with the three-dimensional anatomical information from micro-computed tomography (CT) of the lung and magnetic resonance imaging (MRI) of the brain. These non-invasive imaging techniques provided longitudinal read-outs on the spatial and temporal distribution of infection following intravenous, intranasal or endotracheal routes of inoculation. Furthermore, the imaging results correlated strongly with the fungal load in the respective organs. By obtaining dynamic and quantitative information about the extent and timing of brain infections for individual animals, we found that dissemination to the brain after primary infection of the lung is likely a late-stage event with a time frame that is variable between animals. This novel tool in Cryptococcus research can aid the identification of host and pathogen factors involved in this process and supports development of novel preventive or therapeutic approaches.