Alkali-resistant bacteria in root canal systems

Impact of N-acetylcysteine (NAC) and calcium hydroxide intracanal medications in primary endodontic infection: a randomized clinical trial

OBJECTIVES

This RCT investigated the impact of N-acetylcysteine (NAC) and calcium hydroxide [Ca(OH)₂] intracanal medications (ICMs) in primary endodontic infection with apical periodontitis (PEIAP).

MATERIALS AND METHODS

Thirty-six teeth with PEIAP were randomly divided into groups according to the ICM: NAC, Ca(OH)₂ + saline solution (SSL), and Ca(OH)₂ + 2% chlorhexidine-gel (2% CHX-gel) (all, n = 12). Root canal samples (RCSs) were collected before (s1) and after instrumentation (s2) and after 14 days of ICM (s3). Chemomechanical preparation (CMP) was performed with a Reciproc file and 2.5% NaOCl. Checkerboard DNA-DNA hybridization was used to assess 40 target bacteria species.

RESULTS

At s1, bacterial DNA was detected in 100% of RCSs (36/36). All 40 bacterial species were found in PEIAP. The mean number of species per RCS was 17.92 ± 13.18. The most frequent bacteria were S. mitis (65%), E. nodatum (63%), E. faecalis (63%), F. nucl sp vicentii (58%), T. forsythia (58%), and F. periodonticum (56%). CMP reduced the mean number of species per RCS to 6.8 ± 2.36 (p < 0.05). At s3, the intragroup analysis revealed a broader antimicrobial activity for Ca (OH)₂ + 2% CHX-gel and NAC than Ca(OH)₂ + SSL (p < 0.05). NAC eliminated 8/12 bacteria species resistant to both Ca (OH)₂ ICMs, including P. micra, P. nigrescens, T. denticola, A. israelii, P. endodontalis, P. acnes, C. ochracea, and E. corrodens.

CONCLUSIONS

Ca (OH)2 + 2% chlorhexidine gel (2% CHX gel) showed a greater bacterial elimination over the number of bacterial species; however, NAC eliminated 8/12 bacteria species resistant to both Ca (OH)2 ICMs (RBR-3xbnnn).

CLINICAL RELEVANCE

The use of intracanal medication with a broad antimicrobial activity can optimize root canal disinfection. Ca(OH)₂ + 2% CHX gel and NAC showed a broader antimicrobial activity than Ca(OH)₂ + SSL against endodontic pathogens in primary root canal infection.

TRIAL REGISTRATION

Brazilian Registry of Clinical Trials (REBEC), No. RBR-3xbnnn.

Impact of N-acetylcysteine (NAC) and calcium hydroxide intracanal medications in primary endodontic infection: a randomized clinical trial

OBJECTIVES

This RCT investigated the impact of N-acetylcysteine (NAC) and calcium hydroxide [Ca(OH)₂] intracanal medications (ICMs) in primary endodontic infection with apical periodontitis (PEIAP).

MATERIALS AND METHODS

Thirty-six teeth with PEIAP were randomly divided into groups according to the ICM: NAC, Ca(OH)₂ + saline solution (SSL), and Ca(OH)₂ + 2% chlorhexidine-gel (2% CHX-gel) (all, n = 12). Root canal samples (RCSs) were collected before (s1) and after instrumentation (s2) and after 14 days of ICM (s3). Chemomechanical preparation (CMP) was performed with a Reciproc file and 2.5% NaOCl. Checkerboard DNA-DNA hybridization was used to assess 40 target bacteria species.

RESULTS

At s1, bacterial DNA was detected in 100% of RCSs (36/36). All 40 bacterial species were found in PEIAP. The mean number of species per RCS was 17.92 ± 13.18. The most frequent bacteria were S. mitis (65%), E. nodatum (63%), E. faecalis (63%), F. nucl sp vicentii (58%), T. forsythia (58%), and F. periodonticum (56%). CMP reduced the mean number of species per RCS to 6.8 ± 2.36 (p < 0.05). At s3, the intragroup analysis revealed a broader antimicrobial activity for Ca (OH)₂ + 2% CHX-gel and NAC than Ca(OH)₂ + SSL (p < 0.05). NAC eliminated 8/12 bacteria species resistant to both Ca (OH)₂ ICMs, including P. micra, P. nigrescens, T. denticola, A. israelii, P. endodontalis, P. acnes, C. ochracea, and E. corrodens.

CONCLUSIONS

Ca (OH)2 + 2% chlorhexidine gel (2% CHX gel) showed a greater bacterial elimination over the number of bacterial species; however, NAC eliminated 8/12 bacteria species resistant to both Ca (OH)2 ICMs (RBR-3xbnnn).

CLINICAL RELEVANCE

The use of intracanal medication with a broad antimicrobial activity can optimize root canal disinfection. Ca(OH)₂ + 2% CHX gel and NAC showed a broader antimicrobial activity than Ca(OH)₂ + SSL against endodontic pathogens in primary root canal infection.

TRIAL REGISTRATION

Brazilian Registry of Clinical Trials (REBEC), No. RBR-3xbnnn.

Feasibility of the crude extracts of Amorphophallus paeoniifolius and Colocasia esculenta as intracanal medicaments in endodontic therapy in comparison to the 940 nm diode laser: An in vitro antimicrobial study

Background/purpose

The elimination and debridement of intracanal bacteria are credited with long-term effectiveness in endodontic therapy. This study aimed to compare the antimicrobial efficacies of Amorphophallus paeoniifolius (Suran), Colocasia esculenta (Aravi) crude extracts as intracanal medicaments with calcium hydroxide (CH), 2% chlorhexidine (CHX) gel, and 940 nm diode laser.

Materials and methods

Fifty-eight intact, single-root, extracted human mandibular premolar teeth were prepared. The samples were sterilized, transferred into microcentrifuge tubes, and inoculated with E. faecalis. The samples were placed in an incubator for three weeks to allow the biofilm to grow. Then the samples were randomly divided into five experimental groups (n = 10), disinfected with Suran, Aravi crude extracts, CH, 2% CHX gel, and a 940 nm diode laser. The negative control group (n = 4) and the positive control group (n = 4). Then the samples were observed under light and scanning electron microscopy to monitor the E. faecalis biofilm. The sampling method was carried out in paper point (intracanal) and Peeso bur (intradentinal). Later the number of colony-forming units was counted and analyzed.

Results

Colony-forming units were significantly reduced in the 2% CHX gel in both sampling methods, while Suran showed lower colony-forming units compared to Aravi and CH. The differences between experimental groups were not statistically significant (P > 0.05) in both sampling methods.

Conclusion

This study showed that the application of Suran and Aravi crude extracts as intracanal medicaments leads to a significant reduction in the number of bacterial colonies compared to CH, 2% CHX gel, and 940 nm diode laser.

Endogenous nitric oxide-generating surfaces via polydopamine-copper coatings for preventing biofilm dispersal and promoting microbial killing

INTRODUCTION

Peri-implantitis is a bacterially induced inflammatory disease which affects the hard and soft tissues around a dental implant. Microbial biofilm formation is an important causative factor in peri-implantitis. The aim of this study is to develop an effective multifunctional surface coating for antimicrobial property and to counteract oral biofilm-associated infections via a single polydopamine copper coating (PDAM@Cu) on titanium implant surface to regulate endogenous nitric oxide (NO) generation.

METHODS

PDAM@Cu coatings were made with different concentrations of CuCl₂ on titanium surfaces with a simple dip coating technique. Coatings were characterised to evaluate Cu concentrations as well as NO release rates from the coatings. Further, salivary biofilms were made on the coatings using Brain Heart Infusion (BHI) media in an anaerobic chamber. Biofilms were prepared with three different mixtures, one of which was saliva only, the second had an addition of sheep's blood, and the third was prepared with NO donors S-nitrosoglutathione (GSNO) and L-glutathione (GSH) in the mixture of saliva and blood to evaluate the effects of endogenously produced NO on biofilms. The effectiveness of coated surfaces on biofilms were assessed using four different methods, namely, crystal violet assay, scanning electron microscopy imaging, 2,3-bis (2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide (XTT) metabolic assay, and live/dead staining.

RESULTS

NO release rates could be controlled with different Cu concentration in PDAM@Cu coatings. NO generated from the PDAM@Cu coatings effectively induced dispersal of biofilms shown by the reduction in biofilm biomass as well as reduced biofilm attachment in samples prepared with blood and NO donors. Cu ions released from the PDAM@Cu coatings resulted in killing of the dispersed bacteria, which was evidenced by the live/dead cell staining and reduced metabolic activity noted from the XTT assay. In contrast, samples prepared with saliva showed no significant reduction in biofilms, indicating the important effect of endogenously generated NO on biofilm dispersal.

CONCLUSION

In conclusion, PDAM@Cu coatings with NO generating surfaces have a dual anti-biofilm function, with a synergistic effect on biofilm dispersal from regulated NO generation and bactericidal effects from Cu ions from the coatings.

Occurrence of two NDM-1-producing Raoultella ornithinolytica and Enterobacter cloacae in a single patient in China: probable a novel antimicrobial resistance plasmid transfer in vivo by conjugation

OBJECTIVES

To identify the general features of acquisition of drug-resistance genes in two multi-drug resistant Enterobacteriaceae strains isolated from a single patient in China.

METHODS

The whole-plasmid was sequenced by Illumina Hiseq 4000 and Pacbio RSII procedures. The plasmid conjugation transfer experiment were performed by the mating-out assay. Drug-resistance genes were amplified by PCR assay.

RESULTS

We identified two New Delhi metallo-β-lactamase type 1(NDM-1)-producing isolates, named Raoultella ornithinolytica B1645-1 and Enterobacter cloacae B1645-2, which shared the same sulfonamide-resistant dihydropteroate synthase sul2 gene and aminoglycoside O-phosphotransferase aph(3'')-Ib gene. A novel antimicrobial resistance plasmid pCYNDM01 was first discovered from the multi-drug resistant R. ornithinolytica B1645-1. Interestingly, plasmid pCYNDM01 carried a Gifsy-2 prophage gene. The bla_NDM-1 gene was located on a novel complex class 1 integron with a structure of sul1-qacEΔ1-ΔISAba125-bla_NDM-1-bla_MBL-trpC-ISCR1-catb8-aacA4-IS1-IS6100-dfrA14-intI1. The carrying the bla_NDM-1 gene plasmid pCYNDM01 was transferred to the E. cloacae B1645-2 recipient strain. This 149.44 kb plasmid pCYNDM01 belonged to the IncFII type.

CONCLUSIONS

A novel antimicrobial resistance plasmid pCYNDM01 was first recovered from a multi-drug resistance R. ornithinolytica B1645-1 isolated from China. The novel complex sul1-type class 1 integron might play an essential role in the mobilization of the bla_NDM-1 gene among different enterobacterial species. The occurrence of plasmid pCYNDM01 transfer from R. ornithinolytica to E. cloacae in vitro by conjugation showed that plasmid pCYNDM01 was a self-conjugative plasmid and might cause dissemination of drug-resistance genes within different enterobacterial species from a single patient in vivo by conjugation. The novel variant F-like T4SS of plasmid pCYNDM01 might be as a tool of R. ornithinolytica B1645-1 for resistance genes transfer. The emergence of the two NDM-1-producing Enterobacteriaceae strains should be attracted China attentions and required to prevent its future prevalence.

Antimicrobial effectiveness of etidronate powder (Dual Rinse® HEDP) and two EDTA preparations against Enterococcus faecalis: a preliminary laboratory study

This study aimed to evaluate the antimicrobial and antibiofilm activity of two chelating agents: ethylenediaminetetraacetic acid (EDTA) combined or not with detergents, and etidronic acid combined with sterile saline. The bacterial inhibitory and bactericidal concentrations (MIC and MBC, respectively) were determined on Enterococcus faecalis ATCC 4083 strain. Antimicrobial tests were performed on a biofilm model after treatment with the chelating agents at different times (1, 3, and 5 min) using a biofilm eradication concentration (MBEC) and confocal laser scanning microscope (CLSM) assays. Quantification of cell biomass and percentage of live and dead cells in the biomass was assessed for each group. The normality of the distributions for each variable was assessed using the D'Agostino and Pearson's omnibus normality test. The comparison of bacterial viability among groups and between any two groups was performed using the non-parametric Kruskal-Wallis one-way analysis of variance and the Dunn's test, respectively. No significant between-group difference was observed regarding biomass reduction. On the other hand, EDTA combined with detergents displayed a substantial increase of the dead bacteria ranging between 35 and 43%; whereas, the number of cells killed in the control group and in the other treated groups always ranged between 1 and 6%, at all experimental times. The addition of detergents to EDTA can improve its anti-biofilm activity by reducing EPS production and enhancing the killing of sessile bacterial cells. Clinical relevance EDTA presents a relevant antimicrobial activity when combined with surface-active agents.

Advancing antimicrobial strategies for managing oral biofilm infections

Effective control of oral biofilm infectious diseases represents a major global challenge. Microorganisms in biofilms exhibit increased drug tolerance compared with planktonic cells. The present review covers innovative antimicrobial strategies for controlling oral biofilm-related infections published predominantly over the past 5 years. Antimicrobial dental materials based on antimicrobial agent release, contact-killing and multi-functional strategies have been designed and synthesized for the prevention of initial bacterial attachment and subsequent biofilm formation on the tooth and material surface. Among the therapeutic approaches for managing biofilms in clinical practice, antimicrobial photodynamic therapy has emerged as an alternative to antimicrobial regimes and mechanical removal of biofilms, and cold atmospheric plasma shows significant advantages over conventional antimicrobial approaches. Nevertheless, more preclinical studies and appropriately designed and well-structured multi-center clinical trials are critically needed to obtain reliable comparative data. The acquired information will be helpful in identifying the most effective antibacterial solutions and the most optimal circumstances to utilize these strategies.

Novel Approaches to the Control of Oral Microbial Biofilms

Effective management of biofilm-related oral infectious diseases is a global challenge. Oral biofilm presents increased resistance to antimicrobial agents and elevated virulence compared with planktonic bacteria. Antimicrobial agents, such as chlorhexidine, have proven effective in the disruption/inhibition of oral biofilm. However, the challenge of precisely and continuously eliminating the specific pathogens without disturbing the microbial ecology still exists, which is a major factor in determining the virulence of a multispecies microbial consortium and the consequent development of oral infectious diseases. Therefore, several novel approaches are being developed to inhibit biofilm virulence without necessarily inducing microbial dysbiosis of the oral cavity. Nanoparticles, such as pH-responsive enzyme-mimic nanoparticles, have been developed to specifically target the acidic niches within the oral biofilm where tooth demineralization readily occurs, in effect controlling dental caries. Quaternary ammonium salts (QAS) such as dimethylaminododecyl methacrylate (DMADDM), when incorporated into dental adhesives or resin composite, have also shown excellent and durable antimicrobial activity and thus could effectively inhibit the occurrence of secondary caries. In addition, custom-designed small molecules, natural products and their derivatives, as well as basic amino acids such as arginine, have demonstrated ecological effects by modulating the virulence of the oral biofilm without universally killing the commensal bacteria, indicating a promising approach to the management of oral infectious diseases such as dental caries and periodontal diseases. This article aims to introduce these novel approaches that have shown potential in the control of oral biofilm. These methods may be utilized in the near future to effectively promote the clinical management of oral infectious diseases and thus benefit oral health.

Effects of prolonged exposure to moderate static magnetic field and its synergistic effects with alkaline pH on Enterococcus faecalis

Static magnetic field (SMF) has been shown to biologically affect various microorganisms, but its effects on Enterococcus faecalis, which is associated with multiple dental infections, have not been reported yet. Besides, Enterococcus faecalis was found to be resistant to the alkaline environment provided by a major dental antimicrobial, calcium hydroxide. Therefore, the antibacterial activity of prolonged exposure to moderate SMF (170 mT) and its possible synergistic activity with alkaline pH (pH = 9) were evaluated in the study. The ability to form a biofilm under these conditions was examined by crystal violet assay. Real-time quantitative PCR was performed to evaluate the relative expression of stress (dnaK and groEL) and virulence (efaA, ace, gelE and fsrC) related genes. As the results indicated, cell proliferation was inhibited after 120 h of SMF exposure. What's more, the combined treatment of SMF and alkaline pH showed significantly improved antimicrobial action when compared to single SMF and alkaline pH treatment for more than 24 h and 72 h respectively. However, the ability to form a biofilm was also enhanced under SMF and alkaline pH treatments. SMF can induce stress response by up-regulating the expression of dnaK and elevate virulence gene expression (efaA and ace). These responses were more significant and more genes were up-regulated including groEL, gelE and fsrC when exposed to SMF and alkaline pH simultaneously. Hence, combination of SMF and alkaline pH could be a promising disinfection strategy in dental area and other areas associated with Enterococcus faecalis infections.

Infections Associated With Streptococcus Constellatus in Children

Streptococcus constellatus is a viridans Streptococcus belonging to the Anginosus group. It was associated with abscesses in 37 children, 80% of whom had acute appendicitis with perforation and abscess formation in 50%. None of the children was <3 years of age.

Antibacterial Properties of Chitosan Nanoparticles and Propolis Associated with Calcium Hydroxide against Single- and Multispecies Biofilms: An In Vitro and In Situ Study

INTRODUCTION

The aim of this study was to evaluate the efficacy of chitosan nanoparticles (CNPs) and ethanolic propolis extract (EPE) incorporated into a calcium hydroxide paste (Ca[OH]₂) to kill bacterial biofilms.

METHODS

Human root canal dentin was infected with Enterococcus faecalis for 21 days and also intraorally for 48 hours followed by incubation in brain-heart infusion for 48 hours to standardize biofilm growth. Ca(OH)₂ pastes associated or not with CNPs or EPE were tested on biofilms for 7 and 14 days. Distilled water was used for control purposes. After the treatment procedures, microbiological analysis was performed to determine the reduction in E. faecalis colonies. Confocal microscopy was used to determine the percentage of cell viability in polymicrobial biofilms before and after the exposure to the experimental intracanal medications.

RESULTS

All experimental pastes were able to significantly reduce the E. faecalis colony-forming units (CFU) after 7 or 14 days (P < .05). However, the CFU reduction was significantly improved when CNPs were incorporated into the Ca(OH)₂ paste (P < .05). The multispecies biofilms treated with Ca(OH)₂ showed similar percentages of bacterial viability to the control regardless of the exposure time (P > .05). The viable cell count significantly dropped in the Ca(OH)₂/CNPs groups for both 7 and 14 days (P < .05), whereas the Ca(OH)₂/EPE groups were only effective in eliminating bacteria during the first 7 days of treatment (P < .05).

CONCLUSIONS

Incorporating CNPs into pastes of Ca(OH)₂ could potentially be beneficial when using interappointment intracanal medications because of their ability to kill bacteria in short- and long-term exposure.

Raoultella spp.-clinical significance, infections and susceptibility to antibiotics

The genus Raoultella belongs to the family of Enterobacteriaceae. Raoultella spp. are Gram-negative, aerobic, non-motile rods. This genus can be distinguished from the genus Klebsiella, in that genus use histamine as the only source of carbon in the medium. Also, Raoultella grow at 4 °C and do not produce gas from lactose at 44.5 °C. Raoultella sp. is known to inhabit natural environments (water, soil, plants). The reservoir of Raoultella is the gastrointestinal tract and upper respiratory tract. Raoultella spp. are opportunistic bacteria, which usually cause infections of the biliary tract, pneumonia and bacteraemia in oncologic and with lower immunity patients. Raoultella planticola and Raoultella ornithinolytica are the most frequently encountered human pathogens among the genus Raoultella. In this review, the current knowledge on Raoultella infections is summarized.

Correlation between Enterococcus faecalis and Persistent Intraradicular Infection Compared with Primary Intraradicular Infection: A Systematic Review

INTRODUCTION

The relationship between Enterococcus faecalis and pulpal or periradicular diseases has been studied for many years; however, whether E. faecalis is correlated with persistent intraradicular infections (teeth after failed endodontic treatments) compared with primary intraradicular infections remains controversial. The objective of this systematic review was to compare the prevalence of E. faecalis in primary and persistent intraradicular infections.

METHODS

An exhaustive literature search combined with specified inclusion criteria was performed to collect all studies comparing the prevalence of E. faecalis in root canals with primary and persistent intraradicular infections. Descriptive statistics were applied first because of the high heterogeneity among studies. Subgroup analysis according to different detecting methods (culture and polymerase chain reaction) and sensitivity analysis was then applied. Meta-analysis was conducted with the help of Stata/SE 12.0 (StataCorp, College Station, TX) after excluding studies with uncertain forms of pulpal and periradicular lesions in their primary infection groups.

RESULTS

The systematic review included 10 studies covering 972 teeth. Among them, 2 studies used the culture technique, 6 studies used polymerase chain reaction, and the other 2 used both techniques. The detection rate of E. faecalis by both methods was higher in persistent infections compared with untreated chronic periapical periodontitis as primary infections. The difference was statistically significant (odds ratio = 7.247; 95% confidence interval, 4.039-13.002).

CONCLUSIONS

E. faecalis is more highly correlated with persistent intraradicular infections compared with untreated chronic periapical periodontitis.

Chitosan-decorated calcium hydroxide microcapsules with pH-triggered release for endodontic applications

The treatment of apical periodontitis (AP) remains challenging because traditional root canal therapy (RCT) outcomes are limited by the complexity of the root canal system, drug toxicity, and host immune factors.

Genome Sequence of Enterobacter cancerogenus YZ1

Enterobacter cancerogenus is usually known as an opportunistic human pathogen. Recently, it has attracted great attention for its capability to produce bioemulsifier, degrade xenobiotics, and resist alkalis and antibiotics. Here we report the complete genome of Enterobacter cancerogenus YZ1, isolated from a bran-feeding Coleoptera insect’s frass.

Treatment of root canal biofilms of Enterococcus faecalis with ozone gas and passive ultrasound activation

INTRODUCTION

Biofilms of resistant species such as Enterococcus faecalis pose a major challenge in the treatment of root canals with established periapical disease. This study examined the effects of gaseous ozone delivered into saline on biofilms of E. faecalis in root canals of extracted teeth with and without the use of passive ultrasonic agitation.

METHODS

Biofilms of E. faecalis were established over 14 days in 70 single roots that had undergone biomechanical preparation followed by gamma irradiation. The presence and purity of biofilms were confirmed using scanning electron microscopy and culture. Biofilms were treated with saline (negative control), 1% sodium hypochlorite for 120 seconds (positive control), ozone (140 ppm ozone in air at 2 L/min delivered into saline using a cannula for 120 seconds), saline with passive ultrasonic activation (70 kHz and 200 mW/cm(2) applied to an ISO 15 file held passively within the canal, for 120 seconds), and ozone followed immediately by ultrasonic agitation. After treatment, samples were taken from the biofilm and serially diluted for plate counting.

RESULTS

Analysis revealed that 1% sodium hypochlorite was the most effective disinfecting agent followed by ozone combined with ultrasonic agitation, ozone alone, and finally ultrasonic alone.

CONCLUSIONS

Although none of the treatment regimes were able to reliably render canals sterile under the conditions used, ozone gas delivered into irrigating fluids in the root canal may be useful as an adjunct for endodontic disinfection.

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.

Co-adhesion and biofilm formation by Fusobacterium nucleatum in response to growth pH

Fusobacterium nucleatum is a Gram-negative anaerobic organism considered to play an important role in the progression of periodontal disease and is commonly found in clinical infections of other body sites. Apart from its metabolic versatility, its cell-surface properties enable it to attach to epithelial cells, collagen, gingival epithelial cells and other bacterial genera, but not with other Fusobacteria. The development of periodontitis is associated with a rise in pH in the gingival sulcus to around 8.5, and this is thought to occur by the catabolism of proteins supplied by gingival crevicular fluid. F. nucleatum is commonly isolated from diseased sites and has also been shown to survive in root canal systems at pH 9.0 after Ca(OH)(2) treatment. In order to survive hostile environmental conditions, such as nutrient deprivation and fluctuating temperature and pH, bacteria form biofilms, which are usually made up of multi-species co-aggregates. We have grown F. nucleatum in a chemostat at a growth rate consistent with that of oral bacteria in vivo and report that, at a growth pH of 8.2, F. nucleatum co-adheres and forms a homogeneous biofilm. Cell-surface hydrophobicity was determined in planktonic and co-adhering cells to characterise the interfacial interactions associated with the response to pH. Cell-surface hydrophobicity was found to increase at pH 8.2 and this was also associated with a decrease in the levels of intracellular polyglucose (IP) and an observed change in the bacterial cell morphology. To our knowledge, these results represent the first study in which F. nucleatum has been shown to co-adhere and form a biofilm, which may be important in the organism's persistence during the transition from health to disease in vivo.

Resistance to acidic and alkaline environments in the endodontic pathogen Enterococcus faecalis

BACKGROUND/AIMS

This study aimed to investigate the biochemical mechanisms employed by the endodontic pathogen Enterococcus faecalis to confer acid- and alkali-resistance and to compare these with the mechanisms of representative oral streptococci.

METHODS

E. faecalis JCM8728, Streptococcus mutans NCTC10449 and Streptococcus sanguinis ATCC10556 were used to assess both acid- and alkali-resistance by examining: (i) growth in complex media; (ii) stability of intracellular pH (pH(in)); (iii) cell durability to leakage of preloaded BCECF (2',7'-bis-(2-carboxyethyl)-5,6-carboxy-fluorescein); and (iv) cell permeability to SYTOX-Green.

RESULTS

Growth was initiated by E. faecalis at pH 4.0-11.0, by S. mutans at pH 4.0-9.0 and by S. sanguinis at pH 5.0-9.0. The pH(in) was similar to the extracellular pH in S. mutans and S. sanguinis at pH 5-10, while the pH(in) of E. faecalis was maintained at approximately 7.5-8.5 when extracellular pH was 7.5-10 and was maintained at levels equivalent to the extracellular pH when pH < 7.5. Cell membranes of E. faecalis were resistant to BCECF leakage when extracellular pH was 2.5-12 and to SYTOX-Green permeability at pH 4-10. The cell membrane durability to extracellular pH in E. faecalis was higher than that observed in the Streptococcus strains.

CONCLUSION

Compared to S. mutans, E. faecalis was found to be equally resistant to acid and more resistant to alkalis. The results suggest that pH-resistance in E. faecalis is attributed to membrane durability against acid and alkali, in addition to cell membrane-bound proton-transport systems. These characteristics may account for why E. faecalis is frequently isolated from acidic caries lesions and from persistently infected root canals where calcium hydroxide medication is ineffective.

Detection of bacteria in endodontic samples by polymerase chain reaction assays and association with defined clinical signs in Italian patients

BACKGROUND/AIMS

The presence of selected bacteria (Enterococcus faecalis, Porphyromonas gingivalis, Prevotella intermedia, Tannerella forsythensis, Treponema denticola) in infected root canals was studied using polymerase chain reaction (PCR) assays, and the association of bacteria with clinical signs of endodontic disease was assessed. The null hypothesis, that no difference could be observed between clinical signs of apical periodontitis and a specific bacterial strain, was tested.

METHODS

Microbial samples were obtained from 62 teeth in 54 patients with endodontic disease. For each tooth, clinical data including patient symptoms were collected. Teeth were categorized by diagnosis as having acute apical periodontitis (AAP, teeth with clinical symptoms but no periapical radiolucency, n=22), chronic apical periodontitis (CAP, teeth with radiolucency but no clinical symptoms, n=15) or exacerbated apical periodontitis (EAP, teeth with symptoms and radiolucency, n=25). Seventy-one percent of cases were primary endodontic infections, and 29% were recurrent ('secondary') endodontic infections (failing cases). PCR assays were used to detect the presence of the selected bacteria.

RESULTS

T. denticola and E. faecalis were each detected in 15 of 62 samples (24%), P. gingivalis in 8 samples (13%), P. intermedia in 5 samples (8%), and T. forsythensis in 4 samples (7%). T. denticola was detected in 56% of teeth with EAP. E. faecalis was found in 60% of teeth with CAP and in 72% of teeth with secondary infection. Statistical analysis demonstrated an association of CAP and secondary endodontic infection with the presence of E. faecalis. (P<0.01). EAP was associated with the presence of T. denticola (P<0.01).

CONCLUSION

T. denticola was associated with symptomatic endodontic disease in the presence of apical bone resorption. E. faecalis was associated with treatment failures. We suggest that these species may play critical roles in endodontic pathology.