Microorganisms from canals of root-filled teeth with periapical lesions

AIM: The objective of the present study was to identify the microbial flora within root canals of teeth with failed root-canal treatment and to determine the association of the various species with clinical features. METHODOLOGY: Sixty root-filled teeth with persisting periapical lesions were selected for this study. During nonsurgical endodontic re-treatment, the root-filling material was removed and the canals were sampled. Microbial sampling, isolation and species determination were performed using advanced microbiological techniques for anaerobic species. The association of microbiological findings with clinical features was investigated. RESULTS: Microorganisms were recovered from 51 teeth. In most cases, one or two strains per canal were found. Of the microbial species isolated, 57.4% were facultative anaerobic species and 83.3% Gram-positive microorganisms. Enterococcus faecalis was the most frequently recovered bacterial species. Obligate anaerobes accounted for 42.6% of the species and the most frequently isolated genera was Peptostreptococcus. which was associated with clinical symptoms (P < 0.01). Significant associations were also observed between: (a) pain or history of pain and polymicrobial infections or anaerobes (P < 0.05): (b) tenderness to percussion and Prevotella intermedia/P. nigrescens (P < 0.05); (c) sinus and Streptococcus spp. (P < 0.001) or Actinomyces spp. (P < 0.01); (d) coronally unsealed teeth and Streptococcus spp. or Candida spp. (both with P < 0.01). CONCLUSION: The microbial flora in canals after failure of root-canal treatment were limited to a small number of predominantly Gram-positive microbial species. Facultative anaerobes, especially E. faecalis, were the most commonly isolated microorganisms, however, polymicrobial infections and obligate anaerobes were frequently found in canals of symptomatic root-filled teeth.     

Microbiological examination of infected dental root canals

OBJECTIVES: The aim of this study was to investigate the root canal microbiota of primary and secondary root-infected canals and the association of constituent species with specific endodontic signs and symptoms. METHODS: Microbial samples were taken from 60 root canals, 41 with necrotic pulp tissues (primary infection) and 19 with failed endodontic treatment (secondary infection). Strict anaerobic techniques were used for serial dilution, plating, incubation and identification. RESULTS: A total of 224 cultivable isolates were recovered belonging to 56 different bacterial species. Individual root canals yielded a maximum of 10 bacterial species. Of the bacterial isolates, 70% were either strict anaerobes or microphilic. The anaerobes most frequently isolated were: Peptostreptococcus micros (35%), Fusobacterium necrophorum (23.3%), Fusobacterium nucleatum (11.7%), Prevotella intermedia/nigrescens (16.7%), Porphyromonas gingivalis (6.7%) and Porphyromonas endodontalis (5%). The root canal microflora of untreated teeth with apical periodontitis was found to be mixed, comprising gram-negative and gram-positive and mostly anaerobic microorganisms and usually containing more than 3 species per canal. On the other hand, facultative anaerobic and gram-positive bacteria predominated in canals with failed endodontic treatment, which harbored 1-2 species per canal. Suggested relationships were found between anaerobes, especially gram-negatives, and the presence or history of pain, tenderness to percussion and swelling (P<0.05). In particular, associations were found between: a) pain (n=29) and P. micros (P<0.01), P. intermedia/nigrescens and Eubacterium spp. (both P<0.05); b) history of pain (n=31) and P. micros (P<0.01) Porphyromonas and Fusobacterium spp. (P<0.05); c) tenderness to percussion (n=29) and Porphyromonas spp. (P<0.01), Peptostreptococcus and Fusobacterium spp. (P<0.001); d) swelling (n=20) and Peptostreptococcus spp. (P<0.01), Porphyromonas and Enterococcus spp. (P<0.05); e) wet canals (n=33) and Porphyromonas and Fusobacterium spp. (P<0.05); f) purulent exudate (n=20) and Porphyromonas, Peptostreptococcus and Fusobacterium spp. (P<0.05); previous endodontic treatment and Enterococcus faecalis, Streptococcus spp., P. micros, F. necrophorum (P<0.05). CONCLUSIONS: Our findings indicate potential complex interactions of species resulting in characteristic clinical pictures which cannot be achieved by individual species alone. They also indicate that the microbiota of primary infected canals with apical periodontitis differs in number and in species from the secondary infected canals by using the culture technique.     

Antibiotic resistance gene transfer between Streptococcus gordonii and Enterococcus faecalis in root canals of teeth ex vivo

Multiple bacterial species coexisting in infected root canals might interact, but evidence for interspecies gene transfer is lacking. This study tested the hypothesis that horizontal exchange of antibiotic resistance can occur between different bacterial species in root canals. Transfer of the conjugative plasmid pAM81 carrying erythromycin resistance between 2 endodontic infection-associated species, Streptococcus gordonii and Enterococcus faecalis, was investigated in an ex vivo tooth model. Equal numbers of each species (one with pAM81 and the other plasmid-free) were combined in prepared root canals of sterilized teeth and incubated at 37 degrees C. At 24 and 72 hours, bidirectional interspecies antibiotic resistance gene transfer was evident in microorganisms recovered from teeth; average transfer frequencies from S. gordonii to E. faecalis were 10(-3) transconjugants per donor and from E. faecalis to S. gordonii were 10(-6) and 10(-7) transconjugants per donor at 24 and 72 hours, respectively. Microbial accumulations were observed on root canal walls with scanning electron microscopy. Horizontal genetic exchange in endodontic infections might facilitate adoption of an optimal genetic profile for survival.     

Bacterial examination of endodontic infections by clonal analysis in concert with denaturing high-performance liquid chromatography

BACKGROUND/AIMS: The aim of this study was to examine the diversity of bacterial species in the infected root canals of teeth associated with endodontic abscesses by cloning and sequencing techniques in concert with denaturing high-performance liquid chromatography. METHODS: Samples collected from five infected root canals were subjected to polymerase chain reaction (PCR) with universal 16S ribosomal DNA primers. Products of these PCRs were cloned and sequenced. Denaturing high-performance liquid chromatography (DHPLC) was used as a screening method to reduce the number of clones necessary for DNA sequencing. RESULTS: All samples were positive for the presence of bacteria and a range of 7-13 different bacteria were found per root canal sample. In total, 48 different oral clones were detected among the five root canal samples. Olsenella profusa was the only species present in all samples. Porphyromonas gingivalis, Dialister pneumosintes, Dialister invisus, Lachnospiraceae oral clone, Staphylococcus aureus, Pseudoramibacter alactolyticus, Peptostreptococcus micros and Enterococcus faecalis were found in two of the five samples. The majority of the taxa were present in only one sample, for example Tannerella forsythia, Shuttleworthia satelles and Filifactor alocis. Some facultative anaerobes that are frequently isolated from endodontic infections such as E. faecalis, Streptococcus anginosus and Lactobacillus spp. were also found in this study. CONCLUSION: Clonal analysis of the microflora associated with endodontic infections revealed a wide diversity of oral species.     

Antimicrobial susceptibility of Enterococcus faecalis isolated from canals of root filled teeth with periapical lesions

AIM: To test, in vitro, the susceptibility to different antibiotics of Enterococcus faecalis isolates from canals of root filled teeth with periapical lesions. METHODOLOGY: Twenty-one E. faecalis isolates, from canals of root filled teeth with persisting periapical lesions, were tested for their antibiotic susceptibilities. The following antibiotics were used: benzylpenicillin, amoxicillin, amoxicillin-clavulanic acid, erythromycin, azithromycin, vancomycin, chloramphenicol, tetracycline, doxycycline, ciprofloxacin and moxifloxacin. Minimal inhibitory concentrations (MICs) for the antimicrobial agents were determined using the E-test System (AB BIODISK, Solna, Sweden), and the E. faecalis strains classified as susceptible or resistant according to the guidelines of National Committee for Clinical Laboratory Standards (NCCLS). The strains were also tested for beta-lactamase production with nitrocefin (Oxoid, Basingstoke, UK). RESULTS: All strains were susceptible to penicillins in vitro, however, the MICs of amoxicillin and amoxicillin-clavulanic acid (MIC(90) = 0.75 microg mL(-1)) were lower than for benzylpenicillin (MIC(90) = 3.0 microg mL(-1)). All strains studied were also susceptible to vancomycin and moxifloxacin, whilst 95.2% were susceptible to chloramphenicol. Amongst the isolates, 85.7% were susceptible to tetracycline and doxycycline and 80.9% to ciprofloxacin. The MIC of erythromycin ranged from 0.38 to >256 microg mL(-1); only 28.5% of the strains were susceptible (MIC < or = 0.5 microg mL(-1)). Limited susceptibility was also observed with azithromycin which was active against only 14.2% of isolates. No strains produced beta-lactamase. CONCLUSION: Enterococcus faecalis isolates were completely susceptible, in vitro, to amoxicillin, amoxicillin-clavulanic acid, vancomycin and moxifloxacin. Most isolates were susceptible to chloramphenicol, tetracycline, doxycycline or ciprofloxacin. Erythromycin and azithromycin were least effective.     

Apical periodontitis development and bacterial response to endodontic treatment. Experimental root canal infections in monkeys with selected bacterial strains

In six monkeys, 160 root canals were inoculated with a combination of four bacterial strains belonging to species Streptococcus milleri, Peptostreptococcus anaerobius, Prevotella oralis, and Fusobacterium nucleatum. In two other monkeys, 24 root canals were inoculated with a five-strain combination consisting of these strains and a strain of Enterococcus faecalis. All strains were previously isolated from an infected monkey root canal. After 8-12 months, survival of the strains was recorded bacteriologically, and the reaction in the periapical region was radiographed. From 180 of 184 root canals, one or more of the bacterial strains were reisolated. The two facultative strains were more frequently reisolated than the anaerobic strains. Apical periodontitis was registered in the periapical region of more than 96% of root canals with reisolated bacteria but in none of those without reisolated bacteria. Endodontic treatment was carried out in two sessions with an interval of 14 d without interappointment dressings, and the effect was evaluated bacteriologically before and after each treatment. The chemo-mechanical treatment reduced significantly the number of strains and bacterial cells. The facultative bacteria were more resistant to the treatment than the anaerobic bacteria. The five-strain combination had a higher survival rate than the four-strain combination.     

Bacteria in the apical 5 mm of infected root canals.

Ten freshly extracted teeth which had carious pulpal exposures and periapical lesions contiguous with the root apex were placed inside an anaerobic chamber and the apical 5 mm of the root canals cultured. In addition to anaerobic incubation, duplicate cultures were incubated aerobically. Fifty strains of bacteria from the 10 root canals were isolated and identified. The most prominent bacteria cultured from the 10 root canals were Actinomyces, Lactobacillus, black-pigmented Bacteroides, Peptostreptococcus, nonpigmented Bacteroides, Veillonella, Enterococcus faecalis, Fusobacterium nucleatum, and Streptococcus mutans. Of the 50 bacterial isolates, 34 (68%) were strict anaerobes. This study demonstrates the presence of predominantly anaerobic bacteria in the apical 5 mm of infected root canals in teeth with carious pulpal exposures and periapical lesions.     

Association of Enterococcus faecalis with different forms of periradicular diseases

Data from culture studies have revealed that Enterococcus faecalis is occasionally isolated from primary endodontic infections but frequently recovered from treatment failures. This molecular study was undertaken to investigate the prevalence of E. faecalis in endodontic infections and to determine whether this species is associated with particular forms of periradicular diseases. Samples were taken from cases of untreated teeth with asymptomatic chronic periradicular lesions, acute apical periodontitis, or acute periradicular abscesses, and from root-filled teeth associated with asymptomatic chronic periradicular lesions. DNA was extracted from the samples, and a 16S rDNA-based nested polymerase chain reaction assay was used to identify E. faecalis. This species occurred in seven of 21 root canals associated with asymptomatic chronic periradicular lesions, in one of 10 root canals associated with acute apical periodontitis, and in one of 19 pus samples aspirated from acute periradicular abscesses. Statistical analysis showed that E. faecalis was significantly more associated with asymptomatic cases than with symptomatic ones. E. faecalis was detected in 20 of 30 cases of persistent endodontic infections associated with root-filled teeth. When comparing the frequencies of this species in 30 cases of persistent infections with 50 cases of primary infections, statistical analysis demonstrated that E. faecalis was strongly associated with persistent infections. The average odds of detecting E. faecalis in cases of persistent infections associated with treatment failure were 9.1. The results of this study indicated that E. faecalis is significantly more associated with asymptomatic cases of primary endodontic infections than with symptomatic ones. Furthermore, E. faecalis was much more likely to be found in cases of failed endodontic therapy than in primary infections.     

The antimicrobial effect of calcium hydroxide in root canals pretreated with 5% iodine potassium iodide

Calcium hydroxide (CH) is often used as a routine interappointment dressing during the endodontic treatment of teeth with apical periodontitis. However, it fails to consistently produce sterile root canals. The present study was set up to find out whether an antimicrobial strategy including the use of CH could be made more effective if: 1) canals were pretreated with 5% iodine potassium iodide (IPI), and 2) the dressing period was extended up to 2 months. Fifty human teeth, with radiographically verified apical periodontitis, were microbiologically sampled. After chemomechanical preparation the canals were pretreated with IPI for 3-7 days. Teeth where microorganisms persisted were then treated with CH for 2 months. Following instrumentation and dressing with IPI, 43 bacterial strains were recovered in 22 of the teeth. Samples obtained after the CH dressing period disclosed growth of 13 facultative and two strict anaerobic strains in 10 teeth. Enterococcus faecalis was identified in two specimens. In conclusion, the present study gave no evidence for an increased antimicrobial effect of CH if it was left for longer periods in the root canal. Although pretreatment with IPI from a quantitative point of view did not seem to add antimicrobial power, it might reduce the frequency of persisting strains of E. faecalis.     

The antimicrobial effect of calcium hydroxide in root canals pretreated with 5% iodine potassium iodide

Abstract— Calcium hydroxide (CH) is often used as a routine interappointment dressing during the endodontic treatment of teeth with apical periodontitis. However, it fails to consistently produce sterile root canals. The present study was set up to find out whether an antimicrobial strategy including the use of CH could be made more effective if: 1) canals were pretreated with 5% iodine potassium iodide (IPI), and 2) the dressing period was extended up to 2 months. Fifty human teeth, with radiographically verified apical periodontitis, were microbiologically sampled. After chemomechanical preparation the canals were pretreated with IPI for 3–7 days. Teeth where microorganisms persisted were then treated with CH for 2 months. Following instrumentation and dressing with IPI, 43 bacterial strains were recovered in 22 of the teeth. Samples obtained after the CH dressing period disclosed growth of 13 facultative and two strict anaerobic strains in 10 teeth. Enterococcus faecalis was identified in two specimens. In conclusion, the present study gave no evidence for an increased antimicrobial effect of CH if it was left for longer periods in the root canal. Although pretreatment with IPI from a quantitative point of view did not seem to add antimicrobial power, it might reduce the frequency of persisting strains of E. faecalis .     

Bacteria isolated after unsuccessful endodontic treatment in a North American population

OBJECTIVE: The purpose of this study was to determine the composition of the microbial flora present in teeth after the failure of root canal therapy in a North American population. These results were then compared with those of the previous Scandinavian studies. STUDY DESIGN: Fifty-four root-filled teeth with persistent periapical radiolucencies were selected for retreatment. After removal of the root-filling material, the canals were sampled with paper points, and by reaming of the apical dentin. Both samples were grown under aerobic and strict anaerobic conditions. Then the bacterial growth was analyzed. RESULTS: The microbial flora was mainly of 1 to 2 strains of predominantly gram-positive organisms. Enterococcus faecalis was the most commonly recovered bacterial species. CONCLUSIONS: Bacteria were cultivated in 34 of the 54 teeth examined in the study. E faecalis was identified in 30% of the teeth with a positive culture.     

Identification of Enterococcus faecalis in root-filled teeth with or without periradicular lesions by culture-dependent and-independent approaches

Enterococcus faecalis is the most commonly found species in root-filled teeth evincing recalcitrant periradicular lesions and as a consequence, a role in causation of endodontic treatment failure has been suggested. The purpose of this study was to evaluate the prevalence of this bacterial species in root-filled teeth with or without periradicular lesions. Identification of E. faecalis was carried out by polymerase chain reaction (PCR) or conventional culture procedures. Overall, E. faecalis was detected by species-specific 16S rRNA gene-based PCR in 40/50 teeth (80%), while culture revealed the occurrence of this species in 8/50 teeth (16%). PCR was significantly more effective than culture in detecting this bacterial species (p < 0.001). Of 27 root-filled teeth with no periradicular lesions, E. faecalis was found in 22 cases (81.5%) by PCR and in five cases (18.5%) by culture. Of 23 root-filled teeth with periradicular lesions, E. faecalis was identified in 18 cases (78%) by PCR and in three cases (13%) by culture. Regardless of the identification technique used, no significant difference was observed when comparing the occurrence of E. faecalis in root-filled teeth with and without periradicular lesions (p > 0.05). Although these findings apparently put into question the status of E. faecalis as the main species causing endodontic treatment failure, other related factors still need to be clarified before this assumption turns into certainty.     

New Bacterial Composition in Primary and Persistent/Secondary Endodontic Infections with Respect to Clinical and Radiographic Findings

Introduction

The aim of the present study was to analyze the microbiota of primary and secondary/persistent endodontic infections of patients undergoing endodontic treatment with respect to clinical and radiographic findings.

Methods

Samples from the root canals of 21 German patients were taken using 3 sequential sterile paper points. In the case of a root canal filling, gutta-percha was removed with sterile files, and samples were taken using sterile paper points. The samples were plated, and microorganisms were then isolated and identified morphologically by biochemical analysis and sequencing the 16S rRNA genes of isolated microorganisms.

Results

In 12 of 21 root canals, 33 different species could be isolated. Six (50%) of the cases with isolated microorganisms were primary, and 6 (50%) cases were endodontic infections associated with root-filled teeth. Twelve of the isolated species were facultative anaerobic and 21 obligate anaerobic. Monomicrobial infections were found for Enterococcus faecalis and Actinomyces viscosus. E. faecalis was most frequently isolated in secondary endodontic infections (33%). Moraxella osloensis was isolated from a secondary endodontic infection that had an insufficient root canal filling accompanied by a mild sensation of pain. A new bacterial composition compromising Atopobium rimae, Anaerococcus prevotii, Pseudoramibacter alactolyticus, Dialister invisus, and Fusobacterium nucleatum was recovered from teeth with chronic apical abscesses.

Conclusions

New bacterial combinations were found and correlated to clinical and radiographic findings, particularly to chronic apical abscesses. M. osloensis was detected in root canals for the second time and only in German patients.     

Polymerase chain reaction identification of microorganisms in previously root-filled teeth in a South Korean population

A large body of evidence indicates that microorganisms are the primary causative agents of endodontic treatment failures. This study intended to assess the occurrence of nine putative endodontic pathogens in root-filled teeth associated with periradicular lesions in a South Korean population using a culture-independent molecular approach. Fourteen root-filled teeth with persistent periradicular diseases were selected for retreatment. After removal of the root canal filling, the canals were sampled, and a polymerase chain reaction assay using taxon-specific oligonucleotide primers was used for microbial detection. Bacteria were present in all cases, as revealed by amplification using ubiquitous 16S rDNA primers. The most frequently detected taxon was Enterococcus faecalis (64%), followed by Streptococcus spp. (21%) and Tannerella forsythensis (14%). The results of this study using a highly sensitive identification method are concurrent with those from other geographical locations using diverse identification methods in that E. faecalis is the main species found in cases of root-filled teeth associated with periradicular lesions.     

根管治疗失败病例根管内微生物检测及药敏试验

目的通过对根管治疗失败病例根管内微生物进行培养检测，了解失败病例根管内菌群特征，同时对检测出的细菌进行药敏试验，为临床根管治疗提供参考。方法选择86例根管治疗失败病例共86颗惠牙，去除根管内充填物后，对根管内细菌取样，进行培养和鉴定，用琼脂稀释法对根管内分离的优势菌进行药敏试验。结果根管治疗失败病例根管中微生物菌群组成以兼性厌氧菌为优势菌，主要以1-2种革兰阳性菌为主，肠球菌是最常检出的细菌。失败病例根管内检出的兼性及专性厌氧菌对青霉素G、甲醛甲酚、甲硝唑敏感。结论细菌与根管治疗失败密切相关，根管治疗失败病例根管内微生物组成有其独特性。临床应选择敏感性药物进行治疗。     

感染根管中6种厌氧菌与症状或体征的相关性研究

目的：应用16S rRNA—PCR技术测定感染根管内6种细菌的检出率,分析根管内细菌种类与临床症状及体征的关系。方法：采集48例感染根管样本,按照临床症状或体征分为自发痛、叩痛、窦道3组,提取样本细菌基因组DNA,用PCR扩增细菌16S rRNA基因片段的方法检测细菌种类,计算检出率。结果：共检测48例样本,其中35例检测到待检细菌,检出率达72.9%。检出率最高的是牙髓卟啉单胞菌（35.4%）,其次是牙龈卟啉单胞菌（31.2%）和粪肠球菌（29.1%）,咽峡炎链球菌为（18.7%）,有2例能检出古菌,轻链球菌未检出。统计学分析显示,牙龈卟啉单胞菌与自发痛、粪肠球菌与窦道分别存在相关性（P〈0.05）。结论：根管感染是由多种细菌造成的;5种细菌是感染根管的优势菌;感染根管内牙龈卟啉单胞菌和粪肠球菌检出与临床相应症状或体征有相关性。     

Photodynamic therapy for endodontic disinfection

The aims of this study were to investigate the effects of photodynamic therapy (PDT) on endodontic pathogens in planktonic phase as well as on Enterococcus faecalis biofilms in experimentally infected root canals of extracted teeth. Strains of microorganisms were sensitized with methylene blue (25 microg/ml) for 5 minutes followed by exposure to red light of 665 nm with an energy fluence of 30 J/cm2. Methylene blue fully eliminated all bacterial species with the exception of E. faecalis (53% killing). The same concentration of methylene blue in combination with red light (222 J/cm2) was able to eliminate 97% of E. faecalis biofilm bacteria in root canals using an optical fiber with multiple cylindrical diffusers that uniformly distributed light at 360 degrees. We conclude that PDT may be developed as an adjunctive procedure to kill residual bacteria in the root canal system after standard endodontic treatment.     

Microbial analysis of canals of root-filled teeth with periapical lesions using polymerase chain reaction

The objective of the present study was to investigate the presence of nine bacterial species in root-filled teeth associated with periapical lesions using a polymerase chain reaction analysis and to correlate these species with clinical features of the cases. DNA was extracted from 45 canal samples of root-filled teeth with periapical lesions. A PCR assay using species-specific primers of 16S rDNA and the downstream intergenic spacer region was used for microbial detection. Enterococcus faecalis was the most prevalent species, detected in 77.8% of the study teeth, followed by Peptostreptococcus micros, detected in 51.1%. Porphyromonas gingivalis, Porphyromonas endodontalis, Prevotella intermedia, and Prevotella nigrescens were detected in 35.6%, 22.2%, 11.1%, and 11.1% of the sampled teeth, respectively. Moreover, PCR detected Filifactor alocis in 26.7%, Treponema denticola in 24.4%, and Tannerella forsythia in 4.4% of the samples. T. denticola and P. micros were statistically associated with tenderness to percussion (p < 0.05). P. nigrescens was associated with the presence of spontaneous pain and abscess (p < 0.05). P. endodontalis and P. nigrescens were associated with purulent exudates (p < 0.05). Synergistic relationship was also observed between some species. The results of this study indicated that E. faecalis was the most frequently identified test species by PCR in teeth with failing endodontic treatment.     

Incidence and antimicrobial susceptibility of Porphyromonas gingivalis isolated from mixed endodontic infections

AIM: To investigate the prevalence of Porphyromonas gingivalis in root canals of infected teeth with periapical abscesses and to investigate the antimicrobial susceptibility of this species to some frequently prescribed antibiotics. METHODOLOGY: Samples were obtained from 70 root canals of abscessed teeth. Microbial sampling, isolation and bacterial identification were accomplished using appropriate culture methods for anaerobic species. The antimicrobial susceptibility of the 20 strains of P. gingivalis isolated was determined by using the E-test. The antimicrobial agents tested were amoxicillin, amoxicillin + clavulanate, azythromycin, benzylpenicillin, cephaclor, clindamycin, erythromycin, metronidazole and tetracycline. RESULTS: A total of 352 individual strains, belonging to 69 different species, were isolated. Eighty three percent of the strains were strict anaerobes and 47.5% of the isolated bacteria were Gram-negative. Porphyromonas gingivalis was found in 20 root canals and was most frequently found in symptomatic cases. Statistically, the presence of P. gingivalis was related to purulent exudates and pain on palpation (both P < 0.05). All P. gingivalis strains were sensitive to amoxicillin, amoxicillin + clavulanate, cephaclor, clindamycin, benzylpenicyllin, metronidazole and tetracycline. The lowest range of minimum inhibitory concentration (MIC) (0.026-0.125 microg mL(-1)) was observed against amoxicillin + clavulanate and clindamycin. The lowest MIC 90 was observed against clindamycin (0.064 microg mL(-1)). One strain was resistant to erythromycin and eight strains were resistant to azythromycin. CONCLUSION: Porphyromonas gingivalis pathogen is isolated with frequency from root canals of infected teeth with periapical abscesses. Amoxicillin, as well as amoxicillin-clavulanic acid and benzylpenicillin were effective against P. gingivalis.     

Molecular analysis of the root canal microbiota associated with endodontic treatment failures

Introduction:  The failure of endodontic treatment is usually caused by persistent/secondary intraradicular infections and Enterococcus faecalis has been considered to be the main pathogen involved. Nevertheless, the breadth of bacterial diversity involved with endodontic treatment failures remains to be consistently explored by culture-independent approaches.
Methods:  This study determined the intraradicular microbiota of root-canal-treated teeth with post-treatment apical periodontitis using 16S ribosomal RNA gene clone library analysis.
Results:  Bacteria were present in all cases, confirming the infectious etiology of post-treatment disease. Seventy-four bacterial taxa belonging to six phyla were found in the nine cases investigated. Of these, 55% were identified as as-yet-uncultivated phylotypes, which also made up a significant proportion of the microbiota in many cases. Twenty-five new phylotypes were identified. Most teeth harbored a mixed consortium, with a mean number of 10 taxa per case. Only 11 taxa were found in more than one case, revealing a high interindividual variability in the composition of the microbiota.
Conclusion:  The current findings revealed new candidate endodontic pathogens, including as-yet-uncultivated bacteria and taxa other than E. faecalis , which may participate in the mixed infections associated with post-treatment apical periodontitis.