Cell wall chemical composition of Enterococcus faecalis in the viable but nonculturable state

The viable but nonculturable (VBNC) state is a survival mechanism adopted b y many bacteria (including those of medical interest) when exposed to adver se environmental conditions. In this state bacteria lose the ability to gro w in bacteriological media but maintain viability and pathogenicity and som etimes are able to revert to regular division upon restoration of normal gr owth conditions. The aim of this work was to analyze the biochemical compos ition of the cell wall of Enterococcus faecalis in the VBNC state in compar ison,vith exponentially growing and stationary cells. VBNC enterococcal cel ls appeared as slightly elongated and were endowed with a wall more resista nt to mechanical disruption than dividing cells. Analysis of the peptidogly can chemical composition showed an increase in total cross-linking, which r ose from 39% in growing cells to 48% in VBNC cells. This increase was detec ted in oligomers of a higher order than dimers, such as trimers (24% increa se), tetramers (37% increase), pentamers (65% increase), and higher oligome rs (95% increase). Changes were also observed in penicillin binding protein s (PBPs), the enzymes involved in the terminal stages of peptidoglycan asse mbly with PBPs 5 and 1 being prevalent, and in autolytic enzymes, with a th reefold increase in the activity of latent muramidase-1 in E. faecalis in t he VBNC state. Accessory wall polymers such as teichoic acid and lipoteicho ic acid proved unchanged and doubled in quantity, respectively, in VBNC cel ls in comparison to dividing cells. It is suggested that all these changes in the cell wall of VBNC enterococci are specific to this particular physio logical state. This may provide indirect confirmation of the viability of t hese cells.