Abstract
Over the last ten years, isogenic tagging (IT) has revolutionised the study of bacterial infection dynamics in laboratory animal models. However, quantitative analysis of IT data has been hindered by the piecemeal development of relevant statistical models. The most promising approach relies on stochastic Markovian models of bacterial population dynamics within and among organs. Here we present an efficient numerical method to fit such stochastic dynamic models to in vivo experimental IT data. A common approach to statistical inference with stochastic dynamic models relies on producing large numbers of simulations, but this remains a slow and inefficient method for all but simple problems. Instead, we derive and solve the systems of ordinary differential equations for the two lower-order moments of the stochastic variables (mean, variance and covariance). For any given model structure, and assuming linear dynamic rates, we demonstrate how the model parameters can be efficiently and accurately estimated by divergence minimisation. We then apply our method to an experimental dataset and compare the estimates and goodness-of-fit to those obtained by maximum likelihood estimation. This flexible framework can easily be applied to a range of experimental systems. Its computational efficiency paves the way for model comparison and optimal experimental design.
- A
- number of animals
- T
- number of tagged strains
- n
- number of organs
- Ni
- number of bacteria in organ i
- mij
- migration rate from organ i to organ j
- ki
- killing rate in organ i
- ri
- replication rate in organ i
- τi
- observation time i
- A, B, C
- matrices
- λ
- vector of transition rates
- B
- Number of bootstrap samples
- θ*
- MDE parameter estimate
- ABC
- approximate Bayesian computation
- IT
- isogenic tagging
- LV
- live vaccine
- MARE
- mean absolute relative error
- MDE
- minimum divergence estimate
- MLE
- maximum likelihood estimate
- qPCR
- quantitative polymerase chain reaction
- WITS
- wildtype isogenic tagged strain