A Microbiological Paradox: Viable but Nonculturable Bacteria with Special Reference to Vibrio cholerae

The observation that directly-detectable bacterial cells are unable to grow on bacteriological culture media under certain conditions raises questions regarding the viability of these cells. Various terminologies have been used to describe substrate-responsive and metabolically-active bacterial cells that cannot be cultured. The currently-accepted term is "viable but nonculturable." During the past 15 years, the viable but nonculturable phenomenon has been actively investigated. Bacterial pathogens in the viable but nonculturable state can maintain virulence and produce disease. These organisms may escape detection if bacteriological culture methods are solely used. Thus, methods for direct detection of specific pathogens in food, water and environmental samples are preferable. Viable but nonculturable Vibrio cholerae have been extensively studied, and several sensitive and reliable direct-detection kits have been developed. Viable but nonculturable forms of bacteria are now recognized as a common phenomenon, observable in many bacterial species, which suggests that standard bacteriological laboratory protocols for assessing microbiological safety of food and drinking water are less reliable than direct detection methods.