Models for microbiological colony counts

Concentrations of microorganisms can be estimated from colony counts at different dilutions. However, complications can occur because of colony overlap or inhibition of colony growth. We develop a model of inhibition in which colonies fail to develop if spores are close to spores of other inhibitory species. The model has three parameters, but a limiting case of the model with only two parameters is shown to be more useful in practice. This latter model, which is a generalized linear model, is fitted to colony counts of the fungus Verticillium dahliae and contrasted with a model suggested in an earlier article.