Screening of anti-mycobacterial compounds in a naturally infected zebrafish embryo model

Mycobacterium tuberculosis is a deadly human pathogen that latently infects a third of the worlds population, resulting in approximately 1.5 million deaths per year. Due to the difficulties and expense of carrying out animal drug trials using M. tuberculosis and rodents, infections of the zebrafish Danio rerio with M. marinum have been used as a surrogate. However the methods so far described require specialised equipment and a high level of operator expertise. We investigated a natural infection model where zebrafish embryos are infected through incubation in media containing M. marinum. Using bioluminescently labelled M. marinum, we have characterised the nature of infection and established a model for interventional drug therapy. We have used a selection of traditional and experimental compounds to validate this model for anti-mycobacterial drug discovery. We observed that only three of the six treatments tested (Delamonid, SN30527 and rifampicin) retarded the growth of M. marinum in vitro. In contrast, five of the six treatments (Pretomanid, Delamanid, SN30488, SN30527 and rifampicin) retarded the growth of M. tuberculosis in vitro. Importantly, these same five treatments significantly reduced the bioluminescent signal from naturally infected zebrafish embryos. Overall this study has demonstrated that zebrafish embryos naturally infected with bioluminescent M. marinum M can be used for the rapid screening of anti-mycobacterial compounds with readily available equipment and limited expertise. The result is an assay that can be carried out by a wide variety of laboratories for minimal cost and without high levels of zebrafish expertise.