Factors affecting virulence of Shigella flexneri: strain with relaxed control of ribonucleic acid synthesis.

An Escherichia coli-Shigella flexneri hybrid strain which produces an abortive, nonfatal experimental dysentery has inherited relaxed control of ribonucleic acid synthesis from its E. coli parent. This property, coupled with a partial methionine requirement, has been used to explain its long lag phase in vitro, relative to its Shigella parent. It was suggested that such characteristics may contribute to the hybrid's poor survival in the gut resulting in the abortive infection.