Increase in the Culturable Cell Number of Escherichia coli during Recovery from Saline Stress: Possible Implication for Resuscitation from the VBNC State.

The change in colony-forming units (CFUs) in saline-stressed Escherichia coli cultures was examined. Exposure of E. coli cells to high saline stress decreased the number of CFUs significantly. When the culture was relieved from the stressful condition, the number of CFUs returned within 2 hr to the same level as before the stress. This recovery in the number of CFUs seemed to be independent of DNA synthesis and cell division, because the same phenomenon was also observed in the presence of nalidixic acid. However, the total cell number enumerated by microscopy was the same before and after relief from saline stress. This phenomenon was considered to be the result of the resuscitation of cells that had been in the VBNC state during saline stress. Our method, in which we examined CFU recovery in the presence of a DNA synthesis inhibitor, might be useful for further VBNC study.