The viable but non-culturable state in pathogenic Escherichia coli: A general review

Abstract

Background: The persistence and pathogenicity of pathogenic bacteria are dependent on the ability of the species to survive in adverse conditions. During the infectious process, the organism may need to pass through certain hostile anatomical sites, such as the stomach. Under various environmental stresses, many bacteria enter into the viable but non-culturable (VBNC) state, where they are 'alive' or metabolically active, but will not grow on conventional media. Escherichia coli bacteria encounter several diverse stress factors during their growth, survival and infection and thus may enter into the VBNC state.

Objectives: This review discusses various general aspects of the VBNC state, the mechanisms and possible public health impact of indicator and pathogenic E. coli entering into the VBNC state.

Method: A literature review was conducted to ascertain the possible impact of E. coli entering into the VBNC state.

Results: Escherichia coli enter into the VBNC state by means of several induction mechanisms. Various authors have found that E. coli can be resuscitated post-VBNC. Certain strains of pathogenic E. coli are still able to produce toxins in the VBNC state, whilst others are avirulent during the VBNC state but are able to regain virulence after resuscitation.

Conclusion: Pathogenic and indicator E. coli entering into the VBNC state could have an adverse effect on public health if conventional detection methods are used, where the number of viable cells could be underestimated and the VBNC cells still produce toxins or could, at any time, be resuscitated and become virulent again.

FIGURE 1

Diagrammatical representation of the EnvZ/OmpR osmoregulatory system in Escherichia coli.

FIGURE 2

The viable but non-culturable state.^{, , , ,}