The importance of the viable but non-culturable state in human bacterial pathogens

Abstract

Many bacterial species have been found to exist in a viable but non-culturable (VBNC) state since its discovery in 1982. VBNC cells are characterized by a loss of culturability on routine agar, which impairs their detection by conventional plate count techniques. This leads to an underestimation of total viable cells in environmental or clinical samples, and thus poses a risk to public health. In this review, we present recent findings on the VBNC state of human bacterial pathogens. The characteristics of VBNC cells, including the similarities and differences to viable, culturable cells and dead cells, and different detection methods are discussed. Exposure to various stresses can induce the VBNC state, and VBNC cells may be resuscitated back to culturable cells under suitable stimuli. The conditions that trigger the induction of the VBNC state and resuscitation from it are summarized and the mechanisms underlying these two processes are discussed. Last but not least, the significance of VBNC cells and their potential influence on human health are also reviewed.

Rifamycin action on RNA polymerase in antibiotic-tolerant Mycobacterium tuberculosis results in differentially detectable populations

“…Class II phenotypic tolerance is displayed by almost all of the bacteria in a population under conditions that prevent net growth during exposure to the antibiotic (7). Bacteria in the state originally called VBNC (12) are class II persisters, in that they do not replicate in some standard growth condition-in our case, solid media normally permissive to growth-and are phenotypically tolerant to diverse antibiotics (56,57).…”

“…Phenotypic tolerance to bactericidal antibiotics allows the survival of bacterial "persisters"-a population of organisms that remain viable after exposure to an antimicrobial agent at concentrations that kill the vast majority of an isogenic population at the same concentration under standard replicating conditions (7,12,55). Class I persisters are a small minority arising stochastically in a replicating bacterial population (7).…”

“…Working with Vibrio cholerae and Escherichia coli, Colwell et al first described bacterial populations unable to grow on media rendered semisolid with agar but able to grow in other formats or at later times and termed them "viable but nonculturable" (VBNC) (11). VBNC states have since been described for over 80 bacterial species (12). This is scientifically and medically problematic, as the gold standard for bacterial enumeration introduced by Koch over 130 y ago involves plating dilutions of a culture suspension on semisolid growth medium and counting colony-forming units (cfus).…”

Molecular viability testing of viable but non‐culturable bacteria induced by antibiotic exposure

“…In this state, the bacteria cannot be detected using culture‐based methods, but they remain viable and retain virulence under environmental stressors. Two well‐defined dormancy states, the viable but non‐culturable (VBNC) state and persister cells (persisters), have been described in non‐sporulating bacteria, where they often exhibit strong antibiotic tolerances than culturable cells (viable) (Li et al ., 2014; Maisonneuve and Gerdes, 2014). In the VBNC state, bacteria maintain a low metabolic activity and do not divide, which help them cope with chemical stressors such as chlorination (Oliver et al ., 2005) and antibiotic treatments (Ayrapetyan et al ., 2015a).…”

Survey of verotoxin-producing Escherichia coli and faecal coliforms in beef carcasses destined for export at slaughterhouses in Brazil

“…Another hypothesis is a low pathogen's inoculum size, hindering the growth on an agar plate (Vallières et al, 2013). Also, many bacterial species develop a viable but non-culturable (VBNC) state, characterized by a loss of culturability, therefore impairing their detection by conventional plate count techniques (Li et al, 2014;Pienaar et al, 2016;Ding et al, 2017). Nevertheless, Stx1 production was detected VBNC cells, pointing out the potential health risk of VBNC E. coli O157:H7 (Liu et al, 2010).…”