Quantification of natural growth of two strains of Mycobacterium marinum for translational anti-tuberculosis drug development.

The zebrafish infected with Mycobacterium marinum is an attractive tuberculosis disease model, showing similar pathogenesis to Mycobacterium tuberculosis infections in humans. To translate pharmacological findings from this disease model to higher vertebrates, a quantitative understanding of the natural growth of M. marinum in comparison to the natural growth of M. tuberculosis is essential. Here, the natural growth of two strains of M. marinum, E11 and M(USA) , is studied over an extended period using an established model-based approach, the multistate tuberculosis pharmacometric (MTP) model, for comparison to that of M. tuberculosis. Poikilotherm-derived strain E11 and human-derived strain M(USA) were grown undisturbed up to 221 days and viability of cultures (CFU/mL) was determined by plating at different time points. Non-linear mixed effects modelling using the MTP model quantified the bacterial growth, the transfer between fast-, slow-, and non-multiplying states, and the inoculi. Both strains showed initial logistic growth, reaching a maximum after 20-25 days for E11 and M(USA) , respectively, followed by a decrease to a new plateau. Natural growth of both E11 and M(USA) was best described with Gompertz growth functions. For E11, the inoculum was best described in the slow-multiplying state, for M(USA) in the fast-multiplying state. Natural growth of E11 was most similar to that of M. tuberculosis, while M(USA) showed more aggressive growth behaviour. Characterization of natural growth of M. marinum and quantitative comparison with M. tuberculosis brings the zebrafish tuberculosis disease model closer to the quantitative translational pipeline of anti-tuberculosis drug development.