The viable but nonculturable state in bacteria.

It had long been assumed that a bacterial cell was dead when it was no longer able to grow on routine culture media. We now know that this assumption is simplistic, and that there are many situations where a cell loses culturability but remains viable and potentially able to regrow. This mini-review defines what the "viable but nonculturable" (VBNC) state is, and illustrates the methods that can be used to show that a bacterial cell is in this physiological state. The diverse environmental factors which induce this state, and the variety of bacteria which have been shown to enter into the VBNC state, are listed. In recent years, a great amount of research has revealed what occurs in cells as they enter and exist in this state, and these studies are also detailed. The ability of cells to resuscitate from the VBNC state and return to an actively metabolizing and culturable form is described, as well as the ability of these cells to retain virulence. Finally, the question of why cells become nonculturable is addressed. It is hoped that this mini-review will encourage researchers to consider this survival state in their studies as an alternative to the conclusion that a lack of culturability indicates the cells they are examining are dead.