The human pathogen Mycobacterium tuberculosis and the fish pathogen Mycobacterium marinum trigger the same core set of late immune response genes in zebrafish larvae

Zebrafish is a natural host of various Mycobacterium species and a surrogate model organism for tuberculosis research. Mycobacterium marinum (M. marinum) is evolutionarily most closely related to M. tuberculosis and shares the majority of virulence genes. Although zebrafish is not a natural host of the human pathogen, we have previously demonstrated successful robotic infection of zebrafish embryos with M. tuberculosis and performed drug treatment of the infected larvae. In the present study we examined for how long M. tuberculosis can be propagated in zebrafish larvae and tested a time series of infected larvae to study the transcriptional response via Illumina RNAseq. Granuloma-like structures carrying fluorescently labeled M. tuberculosis could be detected up to 9 days post infection. The continued presence of viable M. tuberculosis in the zebrafish larvae was further confirmed using the molecular bacterial load assay. The infected larvae showed a clear and specific transcriptional immune response with a high similarity to the response of zebrafish larvae infected with the surrogate species M. marinum. We conclude that M. tuberculosis can be propagated in zebrafish larvae for at least one week after infection and provide further evidence that M. marinum is a good surrogate model for M. tuberculosis. Overall design: To study the effect of Mycobacterium tuberculosis (Mtb) infection on gene expression in zebrafish larvae, early embryos were robotically injected into the yolk with Mtb H37rv (Berlin strain) in PVP or with PVP alone. Embryos/larvae were harvested at 0, 1, 2, 3, 4, 5, 6, 8 and 9 days post fertilization (dpf) and used for total RNA extraction. RNA samples derived from 0, 3, 4, 5, 6, and 8 dpf samples were used for Illumina RNA sequencing. Differential gene expression analysis was performed by comparing Mtb-infected samples with PVP-infected control samples (in triplo; except for 8 dpf, which was in duplo).