"How Dead is Dead?"

Hans-Curt Flemming

University of Duisburg-Essen of Germany

September 18, 2008
1:00 p.m., 403B Engineering Hall

This is a surprisingly difficult question, considering microorganisms.  However, a valid and reliable answer is essential, in the first place in the entire medical context, in particular for all disinfection measures.  It is equally essential for aspects of food and beverage, drinking and recreational water safety as well as for the production of pharmaceuticals, cosmetics and many technical processes.  When microorganisms are declared “dead” – how dead are they really?

All depends upon the methods applied for verification of “death”.  It is well known, that the most common technique – cultivability – only reveals a more or less minor fraction of actually viable microorganisms.  How about the rest?

Viability can be demonstrated by a range of culture-independent methods which may reveal remaining cell integrity and physiological activity on various levels, resulting in the recovery of cells which no longer grow on media designed for their detection.  The state of microorganisms after transition from cultivable to non cultivable is characterized by various descriptions such as injured, dormant or “viable-but-non-cultivable” (VBNC).  Inactivation of microorganisms can lead various levels of stress response, may induce repair mechanisms and eventually lead to a state from which cells may recover until final “death” can be confirmed – which obviously depends genuinely on the method applied.

Close this window to return to Calendar page.