Abstract
Under stress conditions, many species of bacteria enter into starvation mode of metabolism or a physiologically viable but non-culturable (VBNC) state. Several human pathogenic bacteria have been reported to enter into the VBNC state under these conditions. The pathogenic VBNC bacteria cannot be grown using conventional culture media, although they continue to retain their viability and express their virulence. Though there have been debates on the VBNC concept in the past, several molecular studies have shown that not only can the VBNC state be induced under in vitro conditions but also that resuscitation from this state is possible under appropriate conditions. The most notable advance in resuscitating VBNC bacteria is the discovery of resuscitation-promoting factor (Rpf), which is a bacterial cytokines found in both Gram-positive and Gram-negative organisms. VBNC state is a survival strategy adopted by the bacteria, which has important implication in several fields, including environmental monitoring, food technology, and infectious disease management; and hence it is important to investigate the association of bacterial pathogens under VBNC state and the water/foodborne outbreaks. In this review, we describe various aspects of VBNC bacteria, which include their proteomic and genetic profiles under the VBNC state, conditions of resuscitation, methods of detection, antibiotic resistance, and observations on Rpf.
Highlights
The viable but non-culturable (VBNC) state is a unique survival strategy adopted by many bacteria in response to adverse environmental conditions
We describe various aspects of VBNC bacteria, which include their proteomic and genetic profiles under the VBNC state, conditions of resuscitation, methods of detection, antibiotic resistance, and observations on resuscitation-promoting factor (Rpf)
When the VBNC concept was proposed some 30 years ago, many issues related to its importance were raised, since there was no demarcation between dying cells and adaptive strategy made by the bacteria to cope with stressful conditions [1]
Summary
The viable but non-culturable (VBNC) state is a unique survival strategy adopted by many bacteria in response to adverse environmental conditions. Vibrio cholerae transformed into coccoid cells in an aquatic microcosm after incubation for 60 days at 4°C [7] In this form, the bacteria remain in the VBNC state and cannot be cultured by conventional laboratory methods. The VBNC Staphylococcus aureus displayed mutational inactivation of catalase (KatA) or superoxide dismutase (SodA) encoded by the genes katA and sodA, respectively These genetic changes rendered the bacterial cells highly susceptible to seawater stress at 4°C, thereby preventing their resuscitability [28]. Several enteric pathogens induced artificially to the VBNC state by exposure to cold conditions were resuscitated by co-culturing them with several eukaryotic cell lines [49]. The reason for this has been attributed to the presence of trace quantities of 5-hydroxymethylfuran-2-carboxylic and furan-2-carboxylic acids in agars [55]
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