Free Access
Vet. Res.
Volume 41, Number 1, January-February 2010
Number of page(s) 10
Published online 02 October 2009
How to cite this article Vet. Res. (2010) 41:08
How to cite this article: Vet. Res. (2010) 41:08
DOI: 10.1051/vetres/2009056

The ability to enter into an avirulent viable but non-culturable (VBNC) form is widespread among Listeria monocytogenes isolates from salmon, patients and environment

Toril Lindbäck1, Martin E. Rottenberg2, Sylvie M. Roche3 and Liv Marit Rørvik1

1  Department of Food Safety and Infection Biology, Norwegian School of Veterinary Science, P.O. Box 8146 Dep., N-0033 Oslo, Norway
2  Microbiology & Tumorbiology Center, Karolinska Institute, Stockholm, Sweden
3  INRA, UR 1282, Infectiologie Animale et Santé Publique, IFR136, Agents transmissibles et Infectiologie, F-37380 Nouzilly, France

Received 12 May 2009; accepted 30 September 2009; published online 02 October 2009

Abstract - Media-based bacteriological testing will fail to detect non-culturable organisms and the risk of consuming viable but non-culturable (VBNC) Listeria monocytogenes is unknown. We have here studied whether L. monocytogenes obtained from seafoods, processing environment and clinical cases enter the VBNC state and assessed the virulence of the non-culturable forms of the bacteria. A number of 16 L. monocytogenes strains were starved in microcosm water at 4 °C until loss of culturability. Metabolic activity in the VBNC form was measured as ATP generation using a luciferase assay and membrane integrity was examined using the LIVE/DEAD BacLight assay. All tested L. monocytogenes strains entered the VBNC state after starvation in microcosm water. Ongoing mRNA synthesis of hly in VBNC L. monocytogenes cells re-incubated in culture medium indicated a potential virulence of these forms. Sodium pyruvate and replenishment of nutrient were used in attempts to resuscitate VBNC cells. However, VBNC L. monocytogenes were not resuscitated under these conditions. VBNC L. monocytogenes were tested for virulence in a cell plaque assay and by intraperitoneally inoculation in immunodeficient RAG1-/- mice. Inoculation of VBNC L. monocytogenes in immunodeficient mice did not cause morbidity, and plaque assay on HT-29 cells in culture indicated that the VBNC cells were avirulent. The results indicate that the risk of non-culturable L. monocytogenes in foods, when the VBNC state is induced by starvation, is negligible.

Key words: Listeria monocytogenes / VBNC / ATP / mRNA

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© INRA, EDP Sciences 2009