VBNC

VBNC stands for viable but non-culturable. It describes a state in which bacteria remain alive and capable of metabolic activity but do not form colonies on standard culture media. VBNC cells retain membrane integrity and energy production, enabling survival under environmental stress. The VBNC state has been observed in many bacterial species and is of particular concern for environmental monitoring and clinical diagnostics because standard culture-based methods may miss them.

Detection and characterization rely on methods beyond plate counts, such as viability stains that assess membrane integrity, metabolic activity assays, RNA-based indicators, and molecular techniques like RT-qPCR. However, distinguishing VBNC cells from truly dead cells can be challenging, because indicators can yield inconclusive results and culturability tests are negative by definition.

Triggers include nutrient limitation, temperature shifts, salinity and osmotic stress, oxidative stress, disinfectants, and antibiotic exposure. VBNC forms have been documented for pathogens such as Vibrio vulnificus and Vibrio cholerae, Listeria monocytogenes, Campylobacter spp., and Escherichia coli O157:H7. In environmental reservoirs and food processing contexts, VBNC cells may persist longer than culturable cells and potentially resuscitate under favorable conditions, posing public health risks.

Resuscitation mechanisms are not fully understood. Some VBNC bacteria can regain culturability in response to specific signals, nutrients, or host-associated environments. The VBNC concept remains debated: some scientists view VBNC as a reversible survival strategy, while others emphasize its status as a technically undetectable subset of dead cells. Regardless, VBNC has important implications for surveillance, risk assessment, and disinfection strategies.