Effects of prolonged exposure to alkaline pH on Enterococcus faecalis survival and specific gene transcripts.
BACKGROUND
The persistence of Enterococcus faecalis in treated root canals has been attributed to its resistance to the high pH of antimicrobial agents used during treatment, but the specific mechanisms are not clear. We investigated the survival and gene expression of E. faecalis maintained in alkaline media.


METHODS
E. faecalis JH2-2 was maintained in media at pH 7, 10, 11 and 12 at either 25 degrees C or 37 degrees C for 1 week (168 h). At 24, 48, 72, 120 and 168 h, cell viability was determined in parallel with real-time quantitative polymerase chain reaction analyses of stress response genes (dnaK, fba, ftsZ, GroEL, napA, pbp5, tsf and tuf).


RESULTS
After 1 week the E. faecalis showed survival levels of 100% in pH 7, 1% in pH 10, 0.001% in pH 11 and 0.00001% in pH 12 media. At 37 degrees C increased levels of gene transcripts occurred between 72 and 120 h in pH 7 media for ftsZ and dnaK, and in pH 10 media for ftsZ, pbp5, dnaK, napA, tsf, fba and GroEL. No increase in transcripts was observed at 37 degrees C in media at pH 11 or pH 12, nor at 25 degrees C in any media.


CONCLUSIONS
Transcripts of ftsZ, a gene involved in cell division, increased by 37-fold after 120 h at pH 10 at 37 degrees C. Overall, the greatest increase in levels of gene transcripts occurred in cultures maintained in pH 10 media at 37 degrees C. These data may assist in understanding the survival strategies of E. faecalis following prolonged exposure to alkaline pH levels.
Appelbe
O K
OK
Department of Cariology, Restorative Sciences and Endodontics, The University of Michigan, School of Dentistry, MI 48109, USA.
Sedgley
C M
CM
D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics*; D002126:Calcium Hydroxide / Q000494:pharmacology; D003598:Cytoskeletal Proteins / Q000096:biosynthesis / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics* / Q000502:physiology*; D013293:Enterococcus faecalis / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D015870:Gene Expression; D006360:Heat-Shock Proteins / Q000096:biosynthesis / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D050296:Microbial Viability / Q000235:genetics*; D016133:Polymerase Chain Reaction / Q000379:methods; D012387:Root Canal Filling Materials / Q000494:pharmacology
D001426:Bacterial Proteins; D003598:Cytoskeletal Proteins; C071525:FtsZ protein, Bacteria; D006360:Heat-Shock Proteins; D012387:Root Canal Filling Materials; D002126:Calcium Hydroxide