Enterococcus faecalis- the root canal survivor and 'star' in post-treatment disease

Occurrence, population structure, and antimicrobial resistance of enterococci in marginal and apical periodontitis

Subgingival plaque samples and root canal samples were collected from 2,839 marginal periodontitis (MP) patients and 21 apical periodontitis (AP) patients. Enterococcus species were identified by a series of phenotypic and genotypic tests. Antimicrobial susceptibility assays were performed by an agar disk diffusion test. Multilocus sequence typing (MLST), eBURST, and minimum spanning tree were used for enterococcal genetic clustering and population analysis. Enterococcus faecalis was recovered from 3.7% MP patients and 9.5% AP patients, and Enterococcus faecium was recovered from 0.04% MP patients. Enterococci were detected more often in older male patients. E. faecalis isolates of MP were found resistant to tetracycline (49.1%), erythromycin (8.5%), trimethoprim (2.8%), and gentamicin (1.9%), while one AP isolate was resistant to tetracycline. A total of 40 sequence types (STs) were resolved in 108 E. faecalis isolates. Comparison with E. faecalis international MLST database revealed that 27 STs were previously found, 13 STs were novel, and several major clonal complexes in the database were also found in MP isolates. The tetracycline-resistant isolates distributed mainly in the major clonal complexes and singletons, whereas the erythromycin-resistant isolates were more dispersed. Although the rate of occurrence of enterococci recovered in the MP and AP samples was low, 50% of these isolates are resistant to at least one antimicrobial agent, which is most often tetracycline. This implies that subgingival E. faecalis might represent a reservoir of resistance to tetracycline and erythromycin. The subgingival E. faecalis isolates show high genetic diversity but are grouped, in general, with the known isolates from the international database.

Efficacy of sodium hypochlorite and chlorhexidine against Enterococcus faecalis--a systematic review

The efficacy of the sodium hypochlorite (NaOCl) and chlorhexidine (CHX) on Enterococcus faecalis was evaluated by systematic review and meta-analysis. The search strategies included search in electronic biomedical journal databases (MEDLINE, EMBASE, CENTRAL) and handsearching records, using different matches of keywords for NaOCl, CHX and Enterococcus faecalis. From 41 in vivo studies, 5 studies met the inclusion criteria. In a sample containing 159 teeth, E. faecalis was detected initially in 16 (10%) teeth by polymerase chain reaction (PCR) and 42 (26.4%) teeth by microbial culture techniques. After root canal disinfection, this species was observed in 11 (6.9%) teeth by PCR and 12 (7.5%) teeth by culture. Risk differences of included studies were combined as generic inverse variance data type (Review Manager Version 5.0 _ Cochrane Collaboration, http://www.cc-ims.net, accessed 15 May 2008), taking into account the separate tracking of positive and negative cultures/PCR. The level of statistical significance was set at p<0.05. In conclusion, NaOCl or CHX showed low ability to eliminate E. faecalis when evaluated by either PCR or culture techniques.

EDTA treatment diminishes the antibacterial and anti-adherence effect of calcium hydroxide on Enterococcus faecalis: an in vitro study

This study sought to understand the cell surface characteristics, viability and biofilm-forming potential ofEnterococcus faecaliscells sequentially exposed to EDTA and calcium hydroxide, as in endodontic treatment. Bacterial cells exposed to EDTA and calcium hydroxide were assayed for cell viability, membrane integrity, cell surface hydrophobicity and surface charge, while alteration in the surface topography ofE. faecaliscells was examined using atomic force microscopy (AFM). The bacterial adherence potential to type I collagen was also examined to assess the biofilm-forming capacity ofE. faecaliscells exposed to EDTA and calcium hydroxide. It was found that calcium hydroxide treatment reduced the viability ofE. faecalis. However, prior exposure to EDTA significantly reduced the antibacterial effect of calcium hydroxide (P&lt; 0.05). Calcium hydroxide treatment resulted in impaired cell wall morphology, observed as increased surface roughness and pore formation under AFM. However, these topographical changes induced by calcium hydroxide were significantly reduced in EDTA pretreated cells (P&lt; 0.05). Calcium hydroxide treatment caused reduction in hydrophobicity and adherence ofE. faecalisto type I collagen. These effects due to calcium hydroxide were also significantly altered in EDTA-pretreated cells (P&lt; 0.001). The findings from this study showed that the antibacterial and anti-adherence effect of calcium hydroxide was diminished by prior exposure ofE. faecaliscells to EDTA.

Leakage of food-borne Enterococcus faecalis through temporary fillings in a simulated oral environment

AIM

To evaluate the hypothesis that food-borne viable Enterococcus faecalis cells could enter the root canal space via coronal leakage.

METHODOLOGY

In a simulated oral environment under mastication the capacity of a calcium sulphate-based temporary filling material (Cavit W) to prevent leakage of E. faecalis from a cheese through the endodontic access cavity into the pulp chamber was assessed. Standardized class I access cavities were prepared in human maxillary molars. These were filled with Cavit of either 2 or 4 mm thickness (n=16, each). Empty access cavities served as positive, teeth filled with a light-curing composite material acted as negative controls (n=8, each). A cheese containing viable E. faecalis cells was placed on the occlusal aspects of test and control teeth, which were subsequently subjected to 680 mastication loads per day for 1 week in a masticator device perfused with artificial saliva at 37 degrees C. Leakage of E. faecalis from the cheese into the pulp chamber was assessed by culture on a kanamycin aesculin azide agar and compared between groups using Fisher's exact test.

RESULTS

All of the positive controls showed pure growth of E. faecalis. In addition, one of the negative control teeth leaked. The 4 mm application of Cavit prevented leakage of E. faecalis significantly better than the corresponding 2 mm application: 1 of 16 specimens compared with 6 of 16 specimens had leakage, respectively (P<0.05).

CONCLUSIONS

The current results substantiate the suspicion that food-derived microbiota could enter the necrotic root canal system via microleakage.

Effects of prolonged exposure to alkaline pH on Enterococcus faecalis survival and specific gene transcripts

INTRODUCTION

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.

CONCLUSION

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.

Photophysical, photochemical, and photobiological characterization of methylene blue formulations for light-activated root canal disinfection

Tissue-specific modification of treatment strategy is proposed to increase the antimicrobial activity of light-activated therapy (LAT) for root canal disinfection. Methylene blue (MB) dissolved in different formulations: water, 70% glycerol, 70% poly ethylene glycol (PEG), and a mixture of glycerol:ethanol:water (30:20:50) (MIX), is analyzed for photophysical, photochemical, and photobiological characteristics. Aggregation of MB molecules, as evident from monomer to dimer ratio, depends on the molar concentrations of MB, which is significantly higher in water compared to other formulations. MIX-based MB formulation effectively penetrates the dentinal tubules. Although, the affinity of MB for Enterococcus faecalis (gram positive) and Actinomycetes actinomycetemcomitans (gram negative) was found to be high in the water-based formulation, followed by MIX, the MIX-based formulation significantly enhanced the model substrate photooxidation and singlet oxygen generation compared to MB dissolved in other formulations. Finally, the efficacy of LAT is evaluated on biofilms produced by both organisms under in vitro and ex vivo conditions. A dual-stage approach that applies a photosensitization medium and an irradiation medium separately is tested. The MIX-based photosensitization medium in combination with dual-stage approach demonstrates thorough disinfection of the root canal with bacterial biofilms. This method will have potential application for root canal disinfection.

Comparative analysis of virulence determinants and mass spectral profiles of Finnish and Lithuanian endodontic Enterococcus faecalis isolates

INTRODUCTION

Putative virulence factors of Enterococcus faecalis have been proposed by several workers and, by analogy, these have been linked to strains of endodontic origin. However, their distribution within the cell population is unknown. In the present study, isolates were taken from the dental root canals of two defined human populations, Lithuanian and Finnish, and examined for a range of virulence properties. In addition, surface-associated molecules and intracellular proteins were compared using matrix-assisted laser desorption-ionization/mass spectrometry (MALDI-TOF-MS) and ProteinChip capture/MS (SELDI-TOF-MS), respectively.

METHODS

Twenty-three Lithuanian and 35 Finnish dental root canal isolates were included. The esp, gelE, ace and efaA genes were detected by polymerase chain reaction, and cytolysin and gelatinase phenotypes were determined by hydrolysis of horse blood agar and gelatine agar, respectively. Protein extracts and surface-associated molecules of whole cells were analysed by SELDI-TOF-MS and MALDI-TOF-MS, respectively.

RESULTS

Presence of esp (n = 15), cytolysin (n = 9), ace (n = 55) and efaA (n = 58) was not statistically different in the two samples, whereas gelE and gelatinase production was detected more frequently in the Finnish material (chi-squared, P < 0.01). Analysis of protein profiles by SELDI-TOF-MS showed clustering of cytolysin-producing strains, whereas MALDI-TOF-MS generated profiles that clustered according to the samples' origin and, furthermore, to atypical quinupristin-dalfopristin susceptibility.

CONCLUSION

A high prevalence of virulence factors was demonstrated in both population types. SELDI-TOF-MS and MALDI-TOF-MS proved useful in distinguishing between different E. faecalis phenotypes and they may be useful technologies for elucidating the eco-distribution of E. faecalis in humans.

The use of calcium hydroxide, antibiotics and biocides as antimicrobial medicaments in endodontics

Bacteria have been implicated in the pathogenesis and progression of pulp and periapical diseases. The primary aim of endodontic treatment is to remove as many bacteria as possible from the root canal system and then to create an environment in which any remaining organisms cannot survive. This can only be achieved through the use of a combination of aseptic treatment techniques, chemomechanical preparation of the root canal, antimicrobial irrigating solutions and intracanal medicaments. The choice of which intracanal medicament to use is dependent on having an accurate diagnosis of the condition being treated, as well as a thorough knowledge of the type of organisms likely to be involved and their mechanisms of growth and survival. Since the disease is likely to have been caused by the presence of bacteria within the root canal, the use of an antimicrobial agent is essential. Many medicaments have been used in an attempt to achieve the above aims but no single preparation has been found to be completely predictable or effective. Commonly used medicaments include calcium hydroxide, antibiotics, non-phenolic biocides, phenolic biocides and iodine compounds. Each has advantages and disadvantages, and further research is required to determine which is best suited for root canal infections.

Antimicrobial efficacy of ozonated water, gaseous ozone, sodium hypochlorite and chlorhexidine in infected human root canals

AIM

To determine the antimicrobial efficacy of ozonated water, gaseous ozone, sodium hypochlorite and chlorhexidine in human root canals infected by Enterococcus faecalis.

METHODOLOGY

Thirty human maxillary anterior teeth were prepared and inoculated with E. faecalis for 60 days. Eppendorf tubes were connected to the coronal portion of the teeth. Urethane hoses were attached to the tubes and to the entrance of a peristaltic pump. The exit of the apparatus corresponded to the apical portion of the root canals. The test irrigating solutions were ozonated water, gaseous ozone, 2.5% sodium hypochlorite (NaOCl), 2% chlorhexidine that circulated at a constant flow of 50 mL min(-1) for 20 min. Samples from the root canals were collected and immersed in 7 mL Letheen Broth (LB), followed by incubation at 37 degrees C for 48 h. Bacterial growth was analysed by turbidity of the culture medium and subculture on a specific nutrient broth. A 0.1 mL inoculum obtained from LB was transferred to 7 mL of brain heart infusion and incubated at 37 degrees C for 48 h. Bacterial growth was checked by turbidity of the culture medium carried out in triplicate.

RESULTS

No solution used as an irrigant over a 20-min contact time demonstrated an antimicrobial effect against E. faecalis.

CONCLUSION

The irrigation of infected human root canals with ozonated water, 2.5% NaOCl, 2% chlorhexidine and the application of gaseous ozone for 20 min was not sufficient to inactivate E. faecalis.

Coaggregation interactions between oral and endodontic Enterococcus faecalis and bacterial species isolated from persistent apical periodontitis

Interactions between Enterococcus faecalis and other species found in root canal infections might be important for the development and persistence of periapical disease. The aim of this study was to investigate the coaggregation interactions between E. faecalis clinical isolates and species previously shown to survive and induce apical periodontitis in monkeys: Peptostreptococcus anaerobius, Prevotella oralis, Fusobacterium nucleatum, and Streptococcus anginosus. Intergeneric coaggregation assays were conducted in duplicate with observations scored immediately at 0 h, 1 h and 24 h after mixing of combinations of strains. All E. faecalis strains (n = 53) coaggregated with F. nucleatum; E. faecalis did not coaggregate with P. anaerobius or S. anginosus. One strain, E. faecalis E1, coaggregated with P. oralis, with aggregates visible at 1 h. Coaggregation interactions between E. faecalis and F. nucleatum observed in this study suggest a potential role for this combination in endodontic infections.

Root Canal Irrigants

Local wound debridement in the diseased pulp space is the main step in root canal treatment to prevent the tooth from being a source of infection. In this review article, the specifics of the pulpal microenvironment and the resulting requirements for irrigating solutions are spelled out. Sodium hypochlorite solutions are recommended as the main irrigants. This is because of their broad antimicrobial spectrum as well as their unique capacity to dissolve necrotic tissue remnants. Chemical and toxicological concerns related to their use are discussed, including different approaches to enhance local efficacy without increasing the caustic potential. In addition, chelating solutions are recommended as adjunct irrigants to prevent the formation of a smear layer and/or remove it before filling the root canal system. Based on the actions and interactions of currently available solutions, a clinical irrigating regimen is proposed. Furthermore, some technical aspects of irrigating the root canal system are discussed, and recent trends are critically inspected.

Enterococcus faecalis-mediated biomineralized biofilm formation on root canal dentinein vitro

Enterococcus faecalis is the most predominant bacteria in teeth with failed root canal therapy and is found to survive harsh conditions prevailing in the root canals of endodontically treated teeth. This study aims to investigate the interaction between E. faecalis and root canal dentine substrate. Towards this end, tooth specimens were prepared and divided into two groups. The tooth specimens in group 1 were incubated with E. faecalis for periods of 2-, 4-, and 6-week intervals and the chemical composition of the biofilm was determined using X-ray diffraction and Fourier transform infrared (FTIR) spectroscopy. The tooth specimens in group 2 were incubated with E. faecalis for a period of 6 weeks and the topography and ultrastructure of the biofilm were examined using scanning electron microscopy (SEM), light microscopy, and laser confocal scanning microscopy. The sediments formed from the bacterial interaction on the dentine (in group 1) were also examined by SEM and FTIR. These experiments highlighted different stages in the interaction of E. faecalis with root canal dentine. Further, a bacterial-induced apatite reprecipitation on mature biofilm was also observed. This ability of E. faecalis to form such calcified biofilm on root canal dentine may be a factor that contributes to their persistence after endodontic treatment.

Apical extrusion of intracanal bacteria following use of two engine-driven instrumentation techniques

AIM

To evaluate the number of bacteria extruded apically from extracted teeth ex vivo after canal instrumentation using the two engine-driven techniques utilizing nickel-titanium instruments (ProTaper and System GT).

METHODOLOGY

Forty extracted single-rooted human mandibular premolar teeth were used. Access cavities were prepared and root canals were then contaminated with a suspension of Enterococcus faecalis and dried. The contaminated roots were divided into two experimental groups of 15 teeth each and one control group of 10 teeth. Group 1, ProTaper group: the root canals were instrumented using ProTaper instruments. Group 2, System GT group: the root canals were instrumented using System GT instruments. Group 3, control group: no instrumentation was attempted. Bacteria extruded from the apical foramen during instrumentation were collected into vials. The microbiological samples from the vials were incubated in culture media for 24 h. Colonies of bacteria were counted and the results were given as number of colony-forming units. The data obtained were analysed using the Kruskal-Wallis one-way analysis of variance and Mann-Whitney U-tests, with alpha = 0.05 as the level for statistical significance.

RESULTS

There was no significant difference as to the number of extruded bacteria between the ProTaper and System GT engine-driven systems (P > 0.05).

CONCLUSIONS

Both engine-driven nickel-titanium systems extruded bacteria through the apical foramen.

What We Leave Behind In Root Canals After Endodontic Treatment: Some Issues and Concerns

The benefits of using sodium hypochlorite (NaOCl) and ethylenediaminetetraacetic acid (EDTA) as endodontic irrigants, and calcium hydroxide as an inter-appointment medicament, are well known to dentists. Many steps undertaken during endodontic treatment and retreatment are rather mechanical in nature, and less attention is committed to understanding the biological issues underlying endodontic treatment and retreatment. It should be noted that dentine is the fundamental substrate in endodontic treatment, and its properties and characteristics are the key determinant of nearly all disease and post-disease processes in the teeth. In this article the effects and counter-effects of NaOCl and EDTA on root canal dentine, and some other related issues are reviewed. This information will enable clinicians to use the beneficial effects of these chemicals, while necessary steps are considered to reduce their harmful effects on dentine substrate.

The Role of Environmental Changes on Monospecies Biofilm Formation on Root Canal Wall by Enterococcus faecalis

Biofilm mode of growth is a strategy in microorganisms to survive harsh growth conditions. Although previous studies have established the ability of Enterococcus faecalis to survive postendodontic environmental conditions, the effect of such conditions on the ultrastructural and physiochemical features of E. faecalis biofilm has received less attention. This study aims to evaluate the effect of different growth conditions on the characteristics of E. faecalis biofilm on root canal, and the penetration of E. faecalis into dentinal tubules. Forty-five intact noncarious human maxillary molars were experimented under nutrient-rich, nutrient-deprived, aerobic, and anaerobic conditions for a period of 21 days. Scanning Electron Microscopy with Energy Dispersive X-ray microanalysis, Laser Confocal Scanning Microscopy and Light microscopic examinations were carried out. The microscopic analysis highlighted a distinct variation in the ultrastructure of the biofilms formed under different experimental conditions. The EDX microanalysis showed a significant increase in the levels of Calcium (Ca) in the biofilm structures formed under anaerobic nutrient-deprived condition (p < 0.001). The depth of bacterial penetration was significantly greater in nutrient-rich condition (p < 0.001). This study demonstrated distinct ultrastructural and physiochemical properties of the biofilms formed and dentinal tubular penetration of E. faecalis under different conditions.