Biological changes of Enterococcus faecalis in the viable but nonculturable state

Abstract

ABSTRACT. Enterococcus faecalis may enter a viable but nonculturable (VBNC) state under adverse conditions. E. faecalis, the major bacterial species present in failed root canal treatments, is thought to survive after endodontic treatment by entering a VBNC state. In this study, we characterized the VBNC state of E. faecalis. We designed 3 different protocols to successfully induce the VBNC state. Approximately one-third of bacteria entered a VBNC state after 15-30 days, and all remained viable for at least 2 months. The morphology, glycometabolism, and adhesion capabilities of VBNC cells differed from those of E. faecalis during the exponential growth phase. Specifically, VBNC E. faecalis cells could not decompose lactose, D-mannitol, or D-sorbitol, although they were able to metabolize sucrose. Transmission electron microscopy showed that the morphology of the VBNC E. faecalis cells changed significantly; the cytoplasmic matrix was unevenly condensed and the overall morphology of the cells became irregular, but the cell membranes remained intact. Although the adhesion ability of the bacteria decreased, VBNC E. faecalis could still adhere to collagen fiber type VBNC state of Enterococcus faecalis I and tooth dentine. The persistence of this adhesion ability may be important in the virulence of VBNC E. faecalis.

Eradication of Enterococcus faecalis Biofilms on Human Dentin

“…The entry of bacteria into a state described as VBNC has been reported repeatedly for a large number of bacterial species, and among them several Gram-positive bacteria, including bacteria that reside in the oral cavity (Hiyari and Bennett, 2011; E et al, 2015). A bacterium in the VBNC state has been defined as a cell which can be demonstrated to be metabolically active, while being incapable of undergoing the sustained cellular division required for growth in or on a medium normally supporting growth of that cell (Koch, 1997).…”

Bactericidal Effect of Triple Antibiotic Paste against Enterococcus faecalis in Dentinal Tubules: An Ex Vivo Study

“…The possible explanation may be that E. faecalis can adapt into a viable, but nonculturable (VBNC), state when exposed to some environmental stresses, and can be resuscitated later in a suitable environment ( 24 ). Previous studies indicated that E. faecalis entered a VBNC state within 2 weeks and remained viable for at least 2 months ( 25 , 26 ). When entering the VBNC state, the E. faecalis shape changed from coccoid to irregular, and it lost its ability to break down lactose, D-mannitol and D-sorbitol ( 24 ).…”

“…When entering the VBNC state, the E. faecalis shape changed from coccoid to irregular, and it lost its ability to break down lactose, D-mannitol and D-sorbitol ( 24 ). Furthermore, the cells can still attach to dentine and Type I collagen fibres, but cannot penetrate the dentinal tubules ( 25 ). These situations might lower the pathogenicity of the bacteria; however, the resuscitated cells can initiate infection after recovery.…”