Original article
Environmental and physico-chemical factors induce
VBNC state in Listeria monocytogenes
Valérie BESNARD, Michel FEDERIGHI, Eric DECLERQ, Florence JUGIAU,
Jean-Michel CAPPELIER*
Unité Mixte de Recherche 1014, Hygiène des Aliments INRA-ENVN, École Nationale
Vétérinaire de Nantes, BP 40706, Route de Gachet, 44307 Nantes, France
(Received 16 August 2001; accepted 12 February 2002)
Abstract – Investigations of bacterial survival in natural environments have indicated that some or-
ganisms lose culturability on appropriate media under certain conditions and yet still exhibit signs of
metabolic activity and thus viability. This reproducible loss of culturability in many bacterial species
led to the description of a “Viable But Non Culturable” (VBNC) state. The purpose of this article is to
determine environmental and physico-chemical factors which induce the VBNC state in a food-borne
pathogen that has become a public concern: Listeria monocytogenes. The factors, i.e. inoculum size,
natural sunlight, temperature (4 oC or 20 oC), NaCl concentration (0% or 7%) and pH (5 or 6) were
studied on 4 strains (LO28, ATCC 19115, Scott A, CNL 895807). The culturability of the starved cell
suspension was determined in each condition tested by the spread plate count, and the cell activity
was determined by the Direct Viable Count technique and CTC-DAPI double staining. A strain effect
was found in different test conditions. For the LO 28 and ATCC 19115 strains, the VBNC state was
very transient in certain conditions. For the other strains tested (Scott A, CNL 895807), the VBNC
state was maintained throughout the observation period. In the dark, the incubation temperature was
the main factor in the production of VBNC forms in L. monocytogenes. However, natural sunlight
rapidly produced the VBNC state in L. monocytogenes cells in microcosm water. We conclude that
because of its ubiquity and the factors studied which are met in the food industry, the presence of
VBNC L. monocytogenes cells could pose a major public healt