Inability of Escherichia coli to Resuscitate from the Viable but Nonculturable State

Abstract

After induction of the viable but nonculturable (VBNC) state in Escherichia coli populations, we have analysed abiotic and biotic factors suggested to promote the resuscitation process. The response to the stressing conditions implied the formation of three subpopulations, culturble VBNC and non viable. In most adverse situations studied, VBNC subpopulation did not represent the dominant fraction. Moreover, this fraction did not remain stable, decreasing along the time. This fact seems to indicate that in most of cases, the VBNC is not a successful phenotype. Our working resuscitation protocol is based on combination of methods of dilution and inhibition of remaining culturable cells in order to unequivocally distinguish between regrowth and resuscitation. Reversion of abiotic factors inducing nonculturability as well as prevention of additional oxidative stress did not provoke resuscitation of VBNC cells. Participation of biotic factors was studied by addition of cell free supernatants from cultures (E. coli STCC 416, Pseudomonas fluorescens CHA0 or Enterococcus faecalis pMW158GFP) with different growth phase. In cases, regardlees of the origin of cell free supernatants, the resuscitation was unsuccessful. These results indicate that the E. coli STCC 416 is not able to resuscitate from the VBNC state. Previously we have stated that VBNC cells release into the surrounding médium molecules which could aid the survival of persisting culturable cells. Combining the E. coli survival and resuscitation processes, the formation of a VBNC subpopulation could be considered as an intentional process, designed for the benefit of the population as a whole