Viable But NonCulturable (VBNC)
Microorganisms that do not grow in culture media, but are still metabolically active and capable of causing infections in animals and plants, are said to be in a VBNC state. Traditional laboratory culture conditions and methods cannot meet the requirements of VBNC organisms to resume growth . Semistarved bacteria usually resume growth immediately when appropriate nutrients and conditions are provided. Viable but nonculturable cells will not resume growth even when nutrients are provided . VBNC cells exhibit active metabolism in the form of respiration or fermentation, incorporate radioactive substrates, and have active protein synthesis but cannot be cultured or grown on conventional laboratory media. They have been detected by observing discrepancies between plate count enumeration of bacterial population and direct staining and microscopic counts . These cells may be a problem in the environment if they are pathogens. For example, viable but nonculturable cells of Vibrio cholerae, enteropathogenic E. coli, Legionella pneumophila, and various other bacteria have been shown to regain culturability after they have entered the intestinal tracts of animals .
The VBNC state is defined as a state of dormancy triggered by harsh environmental conditions such as ;nutrient starvation , extreme temperatures , and sharp changes in pH or salinity ; osmotic stress , oxygen availability , and damage to or lack of an essential cellular component including DNA; exposure to food preservatives and heavy metals ;exposure to white light ; activation of lysogenic phages or suicide genes such as sok/hak or autolysins ; and decontaminating processes such as pasteurization of milk and chlorination of wastewater .