A bacterial spore comprising a modified prkC protein, wherein the extracellular domain of the modified prkC protein binds an agent which is not bound by the extracellular domain of the wild-type prkC protein, and wherein the agent is a germinant that stimulates germination of the bacterial spore, or a bacterial spore comprising a modified gerA protein, wherein the gerA protein has been modified such that the spore undergoes germination in the presence of a germinant which does not stimulate germination of a bacterial spore comprising wild-type gerA protein.