Electron microscopic examination of the morphology of normal Escherichia coli MC4100 and Shigella flexneri cells and their htpR‐defective recombinants has shown the presence in the latter of noncrystalline granules after growth at 37 °C. The defect of the htpR gene leads to some changes in ultrastructure of bacterial colonies and the intensification of the processes of development and aging of colonies as integral structures. These phenomena are manifested by early formation of intercellular contacts and thick surface films as well as the enhanced destruction of microorganisms. The recombinant Shigella strain grown at 30 °C retained its ability to provoke keratoconjunctivitis.