Viable but Nonculturable Gastrointestinal Bacteria and Their Resuscitation

Viable but nonculturable (VBNC) bacteria are deeply dormant phenotypic variants that are characterized by a loss of culturability in conventional culture media, yet retain some viability markers [1]. Thus, low metabolic activity, nutrient uptake, membrane integrity, and respiration are all detectable in these dormant cells. In 1982, the VBNC state was first described for Escherichia coli and Vibrio cholerae [2]. Shortly afterwards, VBNC Salmonella enteriditis were found to regain culturability when placed under favourable conditions [3]. Since then, more than 100 bacterial species (including approximately 30 gastrointestinal bacteria) and some fungi have been reported to enter the VBNC state (see Dong et al. [4] and Li et al. [5] for excellent reviews). Among them are many food-borne, toxin-producing bacteria, such as Aeromonas hydrophila, Bacillus cereus, Campylobacter jejuni, E. coli O157:H7, Lactobacillus acetotolerans, Listeria monocytogenes, S. enterica, Shigella flexneri, V. cholerae, but also probiotic bacteria, such as Bifidobacterium animalis, Bf. longum and Bf. lactis [6].