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Year : 2014  |  Volume : 17  |  Issue : 2  |  Page : 119-123
Evaluation of the presence of Enterococcus Faecalis in root cementum: A confocal laser scanning microscope analysis

1 Department of Conservative and Endodontics, A. B. Shetty Memorial Institute of Dental Science, Mangalore, Karnataka, India
2 Department of Conservative and Endodontics,S.N H.K.E.'S Dental College, Gulbarga, Karnataka, India

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Date of Submission23-Jun-2013
Date of Decision11-Oct-2013
Date of Acceptance21-Dec-2013
Date of Web Publication1-Mar-2014


Aim: The aim of this study is to address the cause of persistent infection of root cementum by Enterococcus faecalis.
Materials and Methods: A sample of 60 human single-rooted teeth were divided into three groups. Group I (control group) had no access opening and one-third of the apical root cementum was sealed using varnish. Group II had no preparation of teeth samples. In group III, apical root cementum was exposed to organic acid and roughened using diamond point to mimic apical resorption. After access opening in groups II and III, all teeth samples were sterilized using gamma irradiation (25 kGy). E. faecalis broth was placed in the root canal and apical one-third of the tooth was immersed in the broth for 8 weeks with alternate day refreshment followed by biomechanical preparation, obturation and coronal seal. Apical one-third of all teeth samples were again immersed in the broth for 8 weeks with alternate day refreshment to mimic secondary infection. The samples were observed under a confocal microscope after splitting the teeth into two halves.
Results: E. faecalis penetrated 160 μm deep into the root cementum in group III samples and only showed adhesion in group II samples.
Conclusion: Penetration and survival of E. faecalis deep inside the cementum in extreme conditions could be the reason for persistent infection.

Keywords: Confocal laser scanning microscope; Enterococcus faecalis; persistent infection; root cementum

How to cite this article:
Halkai R, Hegde MN, Halkai K. Evaluation of the presence of Enterococcus Faecalis in root cementum: A confocal laser scanning microscope analysis . J Conserv Dent 2014;17:119-23

How to cite this URL:
Halkai R, Hegde MN, Halkai K. Evaluation of the presence of Enterococcus Faecalis in root cementum: A confocal laser scanning microscope analysis . J Conserv Dent [serial online] 2014 [cited 2022 Oct 6];17:119-23. Available from:

   Introduction Top

Apical periodontitis is an infection of the area around the root of a tooth, usually caused by bacteria. Although bacterial infection can be substantially reduced by standard intracanal procedures [1] such as intracanal medication and root canal treatment, it is very difficult to render the root canal free of bacteria. This is because bacteria are located in inaccessible areas such as deep inside the dentinal tubules and lateral canals and it is difficult for any intracanal medication to reach these locations. Moreover, bacteria may survive and re-colonize in the areas around the root canal whenever there is opportunity and this may become a primary source of persistent infection. [2] Bacteria are commonly found within dentinal tubules of clinically infected canals. [3] Among these bacteria, Enterococcus faecalis is of interest because it is the most frequently detected species in root-filled teeth with persistent lesions. [4] Some possible factors facilitating the long-term survival of E. faecalis in the root canal system are its ability to invade dentinal tubules, [5] where it can survive for a prolonged period under adverse conditions such as starvation, [6] high pH of calcium hydroxide medication [7] and adhesion of E. faecalis to collagen. Angiotensin-converting enzyme (ACE) and a serine protease (SPR) are the collagen binding proteins produced by E. faecalis. With the help of these proteins, E. faecalis adheres strongly to collagen of dentinal tubule walls. [8] ACE promotes the binding of E. faecalis to type I collagen [9],[10] and in vitro ACE gene expression at 37°C was enhanced in the presence of collagen. [11] In this study, the interaction of E. faecalis with root cementum and its role in persistent infection was investigated.

   Materials and Methods Top

This in vitro study was conducted in the Department of Conservative Dentistry and Endodontics. Teeth sterilization (gamma irradiation at 25 kGy) [12] was performed at Microtol, Bangalore. Data was obtained using an inverted confocal laser scanning microscope (CLSM) (ZEISS LSM 510 META. GmbH, Mannheim, Germany) at the Indian Institute of Science, Bangalore.

A total of 60 human single-rooted teeth recently extracted for orthodontic reasons were collected for the study. After extraction, the teeth were stored in chlorhexidine solution.

Inclusion criteria

Single-rooted, caries-free teeth were examined under ×20 microscope to rule out any cracks, caries, fractures or craze lines and radiographed to confirm the presence of a single canal.

Exclusion criteria

Teeth that had already undergone root canal treatment or teeth with more than one canal, immature root apices, root caries, restorations, fractures or craze lines, thin curved roots and calcified canals were excluded from the study.

The teeth were cleaned off soft-tissues, calculus and stains using sharp hand scalers and thoroughly washed under running tap water to remove any tissue remnants sticking to the tooth surface. The teeth were stored in normal saline solution at room temperature until further use.

All the 60 specimens were randomly divided into three experimental groups as follows:

Group I (n = 20): (Control group) intact teeth with no access cavity preparation and sealing of the root apex was done using varnish.

Group II (n = 20): Access opening was done to gain access to the root canal.

Group III (n = 20): 1 mm of the root apex was exposed to lactic acid (organic acid) at pH below 5.5 to mimic apical demineralization. Apical root cementum was roughened using diamond point to mimic apical resorption that is seen in apical periodontitis cases, followed by access opening to gain access to the root canal.


For the samples in group I (control group), no access preparation was done and apical 1-2 mm of the teeth was sealed with three coats of varnish followed by gamma irradiation of all the samples to eradicate any bacteria that was previously present. For the specimens in groups II and III, access opening and canal debridement were done. The teeth were then subjected to gamma irradiation, followed by inoculation with the E. faecalis broth within the root canal with the help of a micropipette. Simultaneously, apical one-third of the teeth were submerged in the broth for all the teeth samples and incubated for 8 weeks to allow bacterial growth with alternate day refreshment.

Culturing procedure

Streptomycin-resistant strains of E. faecalis (ATCC 29212) were cultured in tryptone soya bean agar broth prepared by mixing 1.8 g powder in 60 ml of distilled water. The prepared broth was sterilized in an autoclave. The E. faecalis strain was inoculated in the broth and placed in an incubator to allow the bacteria to grow at 37°C for 24-48 h. Gram staining was done to confirm bacterial growth. The E. faecalis broth was inoculated within the root canal of the teeth samples with a micropipette. Furthermore, apical one-third of the teeth were submerged in the broth to mimic primary infection. The whole process was refreshed every alternate day for a period of 8 weeks.

After 8 weeks of culturing, the specimens of groups II and III were subjected to biomechanical preparation followed by obturation up to the working length (Root ZX II, J. Morita, Japan). The teeth were instrumented using Protaper Ni-Ti rotary instrument system in a contra-angle gear reduction handpiece (X-Smart Dentsply) and finally obturated with gutta-percha (single-cone technique) using AH plus sealer. After coronal seal, apical one-third of all the samples were again immersed in the E. faecalis broth for 8 weeks with alternate day refreshment to show secondary infection. After the incubation period of 8 weeks, all the samples were washed using 1 ml phosphate buffered saline to remove non-adherent bacteria. A vertical groove was made on buccolingual surface starting from occluso-apical of the all teeth samples using a tapered fissure diamond point. Then with the help of a chisel, each tooth was split into two halves. After coding the teeth samples, the teeth were stained with a fluorescent dye to observe under an inverted CLSM (ZEISS LSM 510 META. GmbH, Mannheim, Germany). The teeth were stained with 50 μL fluorescein diacetate (FDA, Sigma, St. Louis, MO) and 50 μL of propidium iodide (PI, Sigma). FDA is a non-fluorescent, cell-permeable dye. In viable cells, the dye crosses the cell membrane and gets metabolized by intracellular esterases and converted to fluorescein (green) so the viable cells appears green in color. PI is a non-cell permeable, red fluorescent dye, which adheres to ruptured cell membranes so the dead bacteria appear red in color. [13]

   Results Top

For adhesion, we used scoring criteria of 0 (for no adhesion) and 1 (for adhesion). For penetration measured in μm, we used the depth-measuring tool from the CLSM software. Accordingly, results were subjected to statistical analysis using Median test, ANOVA and Student's t-test. [Figure 1] shows live bacteria (green color) and dead bacteria (red color). [Figure 2] shows depth of penetration of E. faecalis in root cementum.

In group I (control group) no access cavity was prepared and at the same time apical one-third of the teeth were sealed with varnish. Results showed no adhesion [Table 1], [Figure 1]a and no penetration of E. faecalis into the root cementum in any of the samples [Table 2], [Figure 2]a.

In group II [14] few samples showed adhesion, mean of adhesion is 0.55 [Table 1], [Figure 1]b but no penetration was seen in any of the samples [Table 2], [Figure 2]b. This means that if an intervention like root canal treatment was done at early stage of infection when no apical changes like demineralization or resorption had taken place, there would be lesser chances of E. faecalis penetration and persistent infection or re-infection.

In group III, apical one-third of the teeth were exposed to acid and apical cementum was roughed to mimic apical periodontitis. In this group, all the samples showed adhesion [Table 1], [Figure 1]c and highest values of penetration was up to 160 μm deep in root cementum [Table 2], [Figure 2]c. This means that delay in treatment leads to changes in apical environment such as apical demineralization and apical resorption, which helps E. faecalis to penetrate deep into cementum and in favorable conditions chances of persistent infection or re-infection also increases. A comparison of values shows high significant difference (P < 0.01) between groups I and III and groups II and III and significant difference (P < 0.05) between groups I and II [Table 1] and [Table 2].
Figure 1: (a) Confocal image showing group I (control group), absence of Enterococcus Faecalis. (b) Group II samples showed adhesion of E. faecalis to root cementum. Red color shows dead E. faecalis and green shows live E. faecalis under confocal laser scanning microscope (CLSM). (c) Group III samples showed penetration of E. faecalis into root cementum. Red color shows dead E. faecalis and green shows live E. faecalis under CLSM

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Figure 2: (a) Depth measuring confocal image showing, group I (control group) absence of Enterococcus Faecalis. (b) Group II samples showing adhesion of E. faecalis up to 1 μm deep under confocal laser scanning microscope (CLSM). (c) Group III samples showed presence of E. faecalis up to 160 μm deep in root cementum under CLSM

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Table 1: Mean and SD of adhesion for three groups. Comparisons between groups with median test

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Table 2: Mean and SD of penetration for three groups. F value calculated by one way ANOVA and comparisons between groups with Student's t-test

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   Discussion Top

In this study, E. faecalis was chosen as the test organism because of its ability to penetrate the root dentin in vitro[12] and it is found up to 90% in persistent infection. [11] E. faecalis has unique properties such as production of ACE and SPR that are collagen binding proteins, which help E. faecalis to adhere strongly to mainly type I and IV collagen present in the root dentin. [12] E. faecalis is a very virulent microorganism, which can survive in alkaline pH and during long starvation periods and then becomes viable in the presence of serum. [7],[15],[16] E. faecalis can survive long periods without any nutrient availability because it can derive nutrients from hyaluronan, which is converted by enzyme hyaluronidase and also derive energy sources from dentinal fluid even in a well-sealed root canal system. Under stress, E. faecalis produces aggregation substance (AS), which helps in bacterial adhesion. [17] Lipoteichoic acids protect E. faecalis against lethal conditions, cytolysin, AS-48 and bacteriocin, which inhibits other bacterial growth. Cytolysin destroys cells such as erythrocytes, PNM cells, macrophages and kills gram-positive microorganisms. [18],[19] Due to this effect there is a shift from gram-positive to gram-negative bacteria. [20] Persistent E. faecalis can cause an inflammatory reaction and may start periradicular damage. [15] The adhesion of E. faecalis to type I and IV collagen [12] is the basis of the present study because apical one-third of the root is made of cellular cementum primarily composed of type IV collagen.

Adhesion is the first step in colonization [12] and our study confirms adhesion and invasion by E. faecalis up to 160 μm into the root cementum [Figure 2]c. However, a previous study showed E. faecalis penetration only up to 150 μm deep into the root dentin. [21] Deeper penetration of E. faecalis in our study is due to the change in apical environment such as demineralization and apical resorption. In group I, there was no invasion or adhesion of E. faecalis as it is a control group. In group II, only few samples showed adhesion, mean of adhesion is 0.55 [Table 1] and no samples showed penetration. On the other hand in group III, all samples showed adhesion [Table 1] and highest penetration into root cementum up to 160 μm [Table 2]. This shows that if early treatment is done after primary infection as in group II, there are less chances of penetration of E. faecalis and re-infection or persistent infection. Whereas in group III, there was delay in treatment at early stages of infection, leading to change in apical environment like demineralization of root cementum and root cementum resorption. These apical changes helped E. faecalis to penetrate deep into the root cementum, thereby increasing the chances of persistent infection or re-infection.

In our study, we cultured for 8 weeks twice because 1 st 8 weeks showed primary infection followed by biomechanical preparation and obturation giving the impression of normal root canal treatment done to subside primary infection. The next 8 weeks of E. faecalis culturing was done to show secondary infection. Group II showed only adhesion but no penetration [Figure 1]b and [Figure 2]b, whereas group III showed deeper penetration. This means irrespective of the primary or secondary infection, what matters most is the apical changes in environment like demineralization or apical resorption, which help E. faecalis to penetrate deep into root cementum and is the cause for re-infection or persistent infection, as confirmed by the samples in group III.

We used gamma irradiation to sterilize the teeth because it does not alter collagen characteristics of the teeth. E. faecalis produces collagen binding protein, [12] with the help of which it adheres strongly to collagen. Other methods of sterilization of teeth samples are by autoclaving, using hot air oven, etc. The disadvantage of autoclave is that it collapses the collagen strands and use of hot air oven makes teeth dehydrated and more brittle. [12]

In our study, data was collected using a CLSM as it has advantages over other methods such as histological samples, which cannot distinguish between viable and dead bacteria. Scanning electron microscope has the disadvantage of multiple steps for sample preparation making it time consuming and also it cannot differentiate between dead and viable bacteria. Fluorescence probe has the disadvantage that it cannot distinguish between viable and dead bacteria and also it cannot show distribution of bacteria. The CLSM (ZEISS LSM 510 META GmbH, Mannheim, Germany) analysis has advantage over other methods to visualize bacteria. [13] Our study confirms that CLSM can give a clear picture about viability and spatial distribution of bacteria.

We used FDA (FDA, Sigma, St. Louis, MO) and PI (PI, Sigma) dyes. FDA is a non-fluorescent cell-permeable dye, which in viable cells crosses the cell membrane, gets metabolized by intracellular esterases and is converted to fluorescein (green). Viable cells appear green in color. PI is non-cell permeable fluorescent dye, which gets adhered to ruptured cell membranes and dead cells appear red in color. [13] Our research confirms the ability of E. faecalis to infect the root cementum.

We used an organic acid (lactic acid) for demineralization of root cementum because the end product of sucrose metabolism is lactic acid. [22]

   Conclusion Top

Demineralization and apical resorption at root cementum plays a significant role in penetration of E. faecalis into root cementum. The severity of infection is directly proportional to depth of penetration of E. faecalis into root cementum. The progress of the disease plays a critical role in the adhesion and penetration of E. faecalis to root cementum.

   Acknowledgment Top

I affirm that I/We have no financial affiliation (e.g., employment, direct payment, stock holdings, retainers, consultant ships and patent licensing arrangements or honoraria), or involvement with any commercial organization with direct financial interest in the subject or materials discussed in this manuscript, nor have any such arrangements existed in the past 3 years. Any other potential conflict of interest is disclosed."

   References Top

1.Byström A, Sundqvist G. Bacteriologic evaluation of the efficacy of mechanical root canal instrumentation in endodontic therapy. Scand J Dent Res 1981;89:321-8.  Back to cited text no. 1
2.Haapasalo M, Orstavik D. In vitro infection and disinfection of dentinal tubules. J Dent Res 1987;66:1375-9.  Back to cited text no. 2
3.Ando N, Hoshino E. Predominant obligate anaerobes invading the deep layers of root canal dentin. Int Endod J 1990;23:20-7.  Back to cited text no. 3
4.Molander A, Reit C, Dahlén G, Kvist T. Microbiological status of root-filled teeth with apical periodontitis. Int Endod J 1998;31:1-7.  Back to cited text no. 4
5.Orstavik D, Haapasalo M. Disinfection by endodontic irrigants and dressings of experimentally infected dentinal tubules. Endod Dent Traumatol 1990;6:142-9.  Back to cited text no. 5
6.Hartke A, Giard JC, Laplace JM, Auffray Y. Survival of Enterococcus faecalis in an oligotrophic microcosm: Changes in morphology, development of general stress resistance, and analysis of protein synthesis. Appl Environ Microbiol 1998;64:4238-45.  Back to cited text no. 6
7.Evans M, Davies JK, Sundqvist G, Figdor D. Mechanisms involved in the resistance of Enterococcus faecalis to calcium hydroxide. Int Endod J 2002;35:221-8.  Back to cited text no. 7
8.Hubble TS, Hatton JF, Nallapareddy SR, Murray BE, Gillespie MJ. Influence of Enterococcus faecalis proteases and the collagen-binding protein, Ace, on adhesion to dentin. Oral Microbiol Immunol 2003;18:121-6.  Back to cited text no. 8
9.Nallapareddy SR, Singh KV, Duh RW, Weinstock GM, Murray BE. Diversity of ace, a gene encoding a microbial surface component recognizing adhesive matrix molecules, from different strains of Enterococcus faecalis and evidence for production of ace during human infections. Infect Immun 2000;68:5210-7.  Back to cited text no. 9
10.Nallapareddy SR, Qin X, Weinstock GM, Höök M, Murray BE. Enterococcus faecalis adhesin, ace, mediates attachment to extracellular matrix proteins collagen type IV and laminin as well as collagen type I. Infect Immun 2000;68:5218-24.  Back to cited text no. 10
11.Nallapareddy SR, Murray BE. Ligand-signaled upregulation of Enterococcus faecalis ace transcription, a mechanism for modulating host-E. faecalis interaction. Infect Immun 2006;74:4982-9.  Back to cited text no. 11
12.Chivatxaranukul P, Dashper SG, Messer HH. Dentinal tubule invasion and adherence by Enterococcus faecalis. Int Endod J 2008;41:873-82.  Back to cited text no. 12
13.Zapata RO, Bramante CM, de Moraes IG, Bernardineli N, Gasparoto TH, Graeff MS, et al. Confocal laser scanning microscopy is appropriate to detect viability of Enterococcus faecalis in infected dentin. J Endod 2008;34:1198-201.  Back to cited text no. 13
14.Rahul H, Mithra NH, Kiran H. Root cementum invasion and adhesion by Enterococcus faecalis confocal analysis. Nitte Univ J Health Sci 2012;2:44-9.  Back to cited text no. 14
15.Sedgley CM, Lennan SL, Appelbe OK. Survival of Enterococcus faecalis in root canals ex vivo. Int Endod J 2005;38:735-42.  Back to cited text no. 15
16.Nerwich A, Figdor D, Messer HH. pH changes in root dentin over a 4-week period following root canal dressing with calcium hydroxide. J Endod 1993;19:302-6.  Back to cited text no. 16
17.Shungu DL, Cornett JB, Shockman GD. Morphological and physiological study of autolytic-defective Streptococcus faecium strains. J Bacteriol 1979;138:598-608.  Back to cited text no. 17
18.Basinger SF, Jackson RW. Bacteriocin (hemolysin) of Streptococcus zymogenes. J Bacteriol 1968;96:1895-902.  Back to cited text no. 18
19.Miyazaki S, Ohno A, Kobayashi I, Uji T, Yamaguchi K, Goto S. Cytotoxic effect of hemolytic culture supernatant from Enterococcus faecalis on mouse polymorphonuclear neutrophils and macrophages. Microbiol Immunol 1993;37:265-70.  Back to cited text no. 19
20.Jackson RW. Bacteriolysis and inhibition of gram-positive bacteria by components of Streptococcus zymogenes lysin. J Bacteriol 1971;105:156-9.  Back to cited text no. 20
21.Sen BH, Piskin B, Demirci T. Observation of bacteria and fungi in infected root canals and dentinal tubules by SEM. Endod Dent Traumatol 1995;11:6-9.  Back to cited text no. 21
22.Cross SE, Kreth J, Wali RP, Sullivan R, Shi W, Gimzewski JK. Evaluation of bacteria-induced enamel demineralization using optical profilometry. Dent Mater 2009;25:1517-26.  Back to cited text no. 22

Correspondence Address:
Rahul Halkai
Department of Conservative and Endodontics, A. B. Shetty Memorial Institute of Dental Science, Mangalore, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0972-0707.128039

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