VIABILITY AND ACTIVITY IN READILY CULTURABLE BACTERIA - A REVIEW AND DISCUSSION OF THE PRACTICAL ISSUES

In microbiology the terms 'viability' and 'culturability' are often eq uated. However, in recent years the apparently self-contradictory expr ession 'viable-but-nonculturable' ('VBNC') has been applied to cells w ith various and often poorly defined physiological attributes but whic h, nonetheless, could not be cultured by methods normally appropriate to the organism concerned. These attributes include apparent cell inte grity, the possession of some form of measurable cellular activity and the apparent capacity to regain culturability. We review the evidence relating to putative VBNC cells and stress our view that most of the reports claiming a return to culturability have failed to exclude the regrowth of a limited number of cells which had never lost culturabili ty. We argue that failure to differentiate clearly between use of the terms 'viability' and 'culturability' in an operational versus a conce ptual sense is fuelling the current debate, and conclude with a number of proposals that are designed to help clarify the major issues invol ved. In particular, we suggest an alternative operational terminology that replaces 'VBNC' with expressions that are internally consistent.