1. ¹Laboratoire de Microbiologie, Département Environnement Microbiologie et Phycotoxines, IFREMER, Plouzané, France
2. ²Laboratoire Environnement Profond, Département Etude des Ecosystèmes Profonds, IFREMER, Plouzané, France
3. ³Groupe de Culture Cellulaire – EA 3879 Unité de Physiologie Comparée et Intégrative, I3S, site CHU Morvan, Brest Cedex, France
4. ⁴Service d'anatomie pathologique, CHU Brest, Brest Cedex, France
5. ⁵Center for Bioinformatics and Computational Biology, University of Maryland, College Park, MD, USA

Correspondence: Dr D Hervio-Heath, Laboratoire de Microbiologie, Département Environnement Microbiologie et Phycotoxines, IFREMER, 29280 Plouzané, France. E-mail: dhervio@ifremer.fr

Received 22 November 2006; Revised 25 January 2007; Accepted 31 January 2007; Published online 10 May 2007.

Abstract

The objective of this study was to explore the recovery of culturability of viable but nonculturable (VBNC) Vibrio parahaemolyticus after temperature upshift and to determine whether regrowth or resuscitation occurred. A clinical strain of V. parahaemolyticus Vp5 was rendered VBNC by exposure to artificial seawater (ASW) at 4°C. Aliquots of the ASW suspension of cells (0.1, 1 and 10 ml) were subjected to increased temperatures of 20°C and 37°C. Culturability of the cells in the aliquots was monitored for colony formation on a rich medium and changes in morphology were measured by scanning (SEM) and transmission (TEM) electron microscopy. Samples of VBNC cells were fixed and examined by SEM, revealing a heterogeneous population comprising small cells and larger, flattened cells. Forty-eight hours after temperature upshift to 20°C or 37°C, both elongation and division by binary fission of the cells were observed, employing SEM and TEM, but only in the 10-ml aliquots. The results suggest that a portion of VBNC cells is able to undergo cell division. It is concluded that a portion of VBNC cells of V. parahaemolyticus subjected to cold temperatures remain viable. After temperature upshift, regrowth of those cells, rather than resuscitation of all bacteria of the initial inoculum, appears to be responsible for recovery of culturability of VBNC cells of V. parahaemolyticus. Nutrient in filtrates of VBNC cells is hypothesized to allow growth of the temperature-responsive cells, with cell division occurring via binary fission, but also including an atypical, asymmetric cell division.