Abstract
The viable but nonculturable (VBNC) state is a unique survival strategy of many bacteria in the environment in response to adverse environmental conditions. VBNC bacteria cannot be cultured on routine microbiological media, but they remain viable and retain virulence. The VBNC bacteria can be resuscitated when provided with appropriate conditions. A good number of bacteria including many human pathogens have been reported to enter the VBNC state. Though there have been disputes on the existence of VBNC in the past, extensive molecular studies have resolved most of them, and VBNC has been accepted as a distinct survival state. VBNC pathogenic bacteria are considered a threat to public health and food safety due to their nondetectability through conventional food and water testing methods. A number of disease outbreaks have been reported where VBNC bacteria have been implicated as the causative agent. Further molecular and combinatorial research is needed to tackle the threat posed by VBNC bacteria with regard to public health and food safety.
Highlights
The cells that form a colony on specific nutrient media are the culturable cells
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 [14]
One study demonstrated that recurrent urinary tract infections in many individuals were caused by uropathogenic E. coli cells which remained in viable but nonculturable cells (VBNC) state [50]
Summary
The cells that form a colony on specific nutrient media are the culturable cells. The cells that are metabolically or physiologically active but cannot be cultured on specific media are the viable but nonculturable cells (VBNC) [1]. Most microorganisms growing in nature have yet to be cultured in the laboratory. Less than 1% of the microorganisms in natural water and soil samples are cultured in viable count procedures [2]. In 1982, Xu and coworkers introduced the term “viable but nonculturable bacterial cells (VBNC)” to distinguish particular cells that could not form colonies on solid media but retained metabolic activity and the ability to elongate after the administration of nutrients [3]. According to Oliver [4], “VBNC can be defined as a metabolically active bacterial cell that crossed a threshold in this way, for known or unknown reasons, and became unable to multiply in or on a medium normally supporting its growth.” Most of the bacteria that enter VBNC state are gram-negative species belonging to the gamma subclass of the proteobacteria branch, except for Rhizobium, Agrobacterium, and Helicobacter-Campylobacter species [5]
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