Modelling host tissue degradation by extracellular bacterial pathogens.

Extracellular bacterial pathogens such as Pseudomonas aeruginosa are able to penetrate into host tissues (given an initial breech in the outer barrier, e.g. a wound) through the action of exo-toxins and degradative exo-enzymes. A mathematical model of this process is presented which, in the absence of significant immune response, predicts the progression of the bacteria into the tissue as a travelling wave whose velocity can be determined explicitly in terms of the model parameters. Simple in vitro experiments in protein-based matrices are performed which yield results consistent with this behaviour. A complementary in vitro experimental system with distinct qualitative behaviour is also studied, giving further insight and confidence in the modelling approach.