Large surface blebs on Escherichia coli heated to inactivating temperatures.

Large surface blebs were observed with phase-contrast optics on Escherichia coli B/r and B(s-1) heated to temperatures at which colony-forming ability was lost. Characterization of such blebs was consistent with the view that they were formed by a physical process and were bounded by the outer membrane of the cell. A hypothesis for thermal inactivation of E. coli is presented that places membrane damage near the primary lethal event.