EN
Population dynamics in batch and continuous culture of Shigella flexneri 3b lysogenic for plaque-less phage X and sensitive to this phag lb serovars have been determined. The abrupt change in the fraction of lysogens resulting from the death, especially of sensitive cells, was observed. The death should result of spontaneous liberation of phage X as concluded from the growth dynamics of the sensitive strain infected with the phage containing bacteria-free filtrate of 3b lysogen. Basing on experimental data mathematical modelling of the dynamics with the use of the differential equation set has been proposed. In the models a qualitative relation between the strains and the phage, estimation of growth parameters and estimated growth curves are given.