Establishment of Zophobas morio larvae as a model for Mycobacterium marinum pathogenesis and treatment assessments

Mycobacterial infection models are important in pathogenesis and treatment research, yet current models have substantial limitations – be them financial, ethical, technical or other. Here we propose the use of the relatively little explored larva Zophobas morio as a convenient model for Mycobacterium marinum infections – both as a tool for M. marinum research per-se, and as a surrogate for M. tuberculosis research. We demonstrate dose-responsive mortality in M. marinum-inoculated larvae, and the lack of mortality in attenuated strains such as an amino-acid auxotroph and an ESX-1 deleted mutant. Use of luminescent bacteria enabled measurement of bacterial proliferation using simple luminescence readings, and fluorescent bacteria could be demonstrated in-vivo by fluorescent microscopy. The efficacy of antibiotics could be demonstrated and compared across antibiotics using simple mortality experiments. Z. morio are cheap, pose relatively few ethical considerations, and are easy to grow, maintain, inoculate and treat by antibiotics. This in-vivo model provides a substantial addition to the toolbox of mycobacterial researchers.