Yoo, A.Rossi-Fedele, G.Kidd, S.Rogers, A.Zilm, P.2018-05-112018-05-112018Journal of Endodontics, 2018; 44(2):269-2730099-23991878-3554http://hdl.handle.net/2440/112020Extracellular material (ECM) surrounding Enterococcus faecalis may play a role in increasing resistance to environmental stresses. Our aim was to determine ECM levels in response to subminimal inhibitory concentrations of sodium hypochlorite (sub-MIC/NaOCl) or anaerobic growth and determine the impact on biofilm development.From 37 E. faecalis clinical strains, 19 were selected according to their biofilm-producing ability by using a crystal violet biofilm assay: 10 strong, 4 intermediate, and 5 non-biofilm producers. Biofilm assays were subsequently performed on all strains when subjected to sub-MIC/NaOCl. All strains were evaluated for ECM production under aerobic and anaerobic conditions and with sub-MIC/NaOCl. ECM production was assessed by using scanning electron microscopy. Double-blinded independent assessors were used to score levels of ECM production. The esp gene was detected by using polymerase chain reaction. Gelatinase activity was determined by using Todd-Hewitt and gelatin agar.In aerobic conditions, ECM was expressed in all strains. In the presence of sub-MIC/NaOCl, of the 10 strong biofilm producers, 5 increased their ECM production, and 4 showed increased biofilm growth. Two strains had less ECM production and showed decreased biofilm growth. One isolate demonstrated no observable changes. Most non-biofilm producers demonstrated no observable differences in ECM production, although 1 strain increased biofilm growth. ECM production in anaerobic conditions was highly variable. The esp gene (n = 15) and gelatinase activity (n = 7) were evident among the isolates.Clonal diversity among strains of E. faecalis suggests that some strong biofilm producers can upregulate ECM production and increase biofilm growth in response to sub-MIC/NaOCl.en© 2017 American Association of Endodontists.BiofilmEnterococcus faecalisclonal diversityextracellular materialstress responseJournal article003007918510.1016/j.joen.2017.08.0250004248572000132-s2.0-85036619784390134Rossi-Fedele, G. [0000-0002-8287-1226]Kidd, S. [0000-0002-2118-1651]Zilm, P. [0000-0001-7554-9717]