Within the life sciences switching mechanisms are pervasive at all levels, from molecules to cells and tissues. Their operation can be a key determinant of health or disease. Whilst the existence and importance of switches is widely acknowledged within the biological literature, many life scientists do not deal explicitly with the switching behaviour. Frequently, steady-state behaviour before and after switching is the primary focus. Here methods for analysis of switched systems from control engineering are applied to the modelling and analysis of a riboswitch. The model has been developed by studying the dynamics of the vitamin B12 riboswitch. The simulation results have been validated using in vivo experiments by checking the bacterial growth when using Escherichia coli and Salmonella enterica where the action of the vitamin B12 riboswitch is known to be a determinant of system behaviour. The paper first describes a simple model for the B12-riboswitch regulatory network in E. coli and applies the same analysis when changing the strain to S. enterica. Validation of the simulation results has been undertaken by linking the dynamics of the riboswitch to bacterial growth.