Identification of Enterococcci isolated from canals of root filled teeth with periapical lesions and their antimicrobial susceptibility to different antibiotics

Aim The objective of the present study was to investigate the occurrence of Enterococcus spp. in root filled teeth with periapical lesions and the in vitro antimicrobial susceptibility of the isolates. Methodology Sixty teeth with failed root canal treatment were included in the study. During nonsurgical endodontic retreatment, the root filling material was removed and the canals were sampled and microbiologically examined. Enterococcus ssp. isolates were tested for their antibiotic susceptibilities using the E‐test system (AB BIODISK, Solna, Sweden). The following antibiotics were used: benzylpenicillin, amoxicillin, amoxicillin‐clavulanic acid, erythromycin, azithromycin, vancomycin, chloramphenicol, tetracycline, doxycycline, ciprofloxacin and moxifloxacin. The strains were also tested for β‐lactamase production with nitrocefin (Oxoid, Hampshire, England). Results Microorganisms were recovered from 51 of 60 teeth. Enterococcus faecalis was recovered from 27 of the 51 canals with bacteria, 18 times in pure culture. All strains were susceptible to penicillins; however, the MICs of amoxicillin and amoxicillin‐clavulanic acid (MIC₉₀ = 0.75 µg mL^?1) were lower than that for benzylpenicillin (MIC₉₀ = 3.0 µg mL^?1). All strains studied were also susceptible to vancomycin and moxifloxacin, while 95.2% were susceptible to chloramphenicol. Among 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 µg mL^?1; only 28.5% of the strains were susceptible (MIC ≤ 0.5 µg mL^?1). Limited susceptibility was also observed with azithromycin, which was active against only 14.2% of isolates. No strains produced β‐lactamase. Conclusions Enterococcus faecalis was present in a large number of canals in teeth with failed root fillings and 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. (Supported by the Brazilian agencies FAPESP 00/13686‐8, 00/13689‐7; CNPq 520277/99‐6 and CAPES BEX2449/02‐1).     

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.     

In vitro antimicrobial susceptibility of oral strains of Actinobacillus actinomycetemcomitans to seven antibiotics

BACKGROUND/AIMS: Periodontal infections with Actinobacillus actinomycetemcomitans seem to be refractory to conventional therapy. The aim of the present study was to test the in vitro susceptibilities of A. actinomycetemcomitans strains to a panel of seven orally administrable antibiotics. METHODS: A total of 60 isolates of A. actinomycetemcomitans recovered from 43 individuals with gingivitis or periodontitis were tested. In addition, laboratory strains UP-6 and JP2 were analysed. The E-test was employed in order to determine minimal inhibitory concentrations (MIC) of antibiotics ampicillin/sulbactam, roxithromycin, azithromycin, doxycycline, metronidazole, ciprofloxacin, and moxifloxacin. RESULTS: A. actinomycetemcomitans was highly susceptible to both fluoro-quinolones (MIC90 of 0.006 microgram/mL of ciprofloxacin and 0.032 microgram/mL of moxifloxacin). Good susceptibilities were found for ampicillin/sulbactam and doxycycline (MIC90 of 0.75 microgram/mL and 1 microgram/mL, respectively), and moderate susceptibilities for azithromycin (MIC90 of 3 microgram/mL). Most strains were resistant to metronidazole and roxithromycin. Cluster analysis revealed two larger clusters of A. actinomycetemcomitans strains with the smaller cluster assembling isolates with significantly higher MICs of most antibiotics. CONCLUSIONS: Due to reported favourable pharmacokinetics, the fluoro-quinolone moxifloxacin appeared to be a promising candidate for adjunctive systemic antibiotic therapy in periodontal infections with A. actinomycetemcomitans.     

Evaluation of root canal microorganisms isolated from teeth with endodontic failure and their antimicrobial susceptibility

Studies of the microbiota from the canals of teeth with failure of endodontic therapy have revealed that it differs markedly from that of untreated necrotic dental pulps. This study aimed to evaluate the microbiota of 30 root-filled teeth with persisting periapical lesions and to test the antibiotic susceptibility of the most prevalent species. Microbial samples, isolation and speciation were done using advanced microbiologic techniques for anaerobic species. A total of 55 bacterial species were isolated, 80% were gram-positives and 58% facultative anaerobic microorganisms. The bacterial genera most frequently recovered were Enterococcus, Streptococcus, Peptostreptococcus and Actinomyces. Antibiotic sensitivity of Enterococcus faecalis and Peptostreptococcus spp. was accomplished with the E-test system. All species studied were susceptible to benzylpenicillin, amoxicillin, amoxicillin combined with clavulanate. However, 20% of the E.faecalis strains were resistant to erythromycin and 60% to azithromycin. It was concluded that microbial flora in canals after endodontic failure comprised predominantly facultative anaerobes and gram-positive species. E.faecalis was the species most frequently isolated and showed erythromycin and azithromycin resistance among the isolates.     

In vitro activity of amoxicillin, clindamycin, doxycycline, metronidazole, and moxifloxacin against oral Actinomyces

Actinomyces spp have been increasingly associated with endodontic infections. However, the antimicrobial susceptibility of this genus has not been studied extensively. The objective of this study was to determine the susceptibility of oral isolates of Actinomyces naeslundii, Actinomyces gerencseriae, Actinomyces israelii, Actinomyces viscosus, and Actinomyces odontolyticus to amoxicillin, clindamycin, doxycycline, metronidazole, and moxifloxacin using in vitro assays. The minimum inhibitory concentration (MIC) of each bacterial isolate was determined by using E-test strips (AB Biodisk, Solna, Sweden). The MIC(90) was 0.19 microg/mL for amoxicillin, 0.25 microg/mL for doxycycline, 0.50 microg/mL for moxifloxacin, and 1.00 microg/mL for clindamycin. However, metronidazole was not active against any of the Actinomyces spp tested (MIC(90)>256 microg/mL).     

Identification and antimicrobial susceptibility of enterococci isolated from the root canal

Enterococci are occurring in opportunistic infections involving the oral cavity. This study has identified enterococcal species in 29 endodontic infections undergoing treatment with Ca (OH)2 dressings. The in vitro antimicrobial susceptibility of 29 isolated enterococcal strains was determined. Enterococcus faecalis was speciated for 26 isolates and Enterococcus faecium for three isolates. In vitro antimicrobial susceptibility testing revealed enterococcal isolates resistant to benzylpenicillin, ampicillin, clindamycin, metronidazole and tetracycline but sensitive to erythromycin and vancomycin. Due to low sensitivity to antimicrobial agents, enterococci may be selected in root canals undergoing standard endodontic treatment and significantly contribute to endodontic treatment failures.     

Virulence, phenotype and genotype characteristics of endodontic Enterococcus spp

BACKGROUND/AIMS: Enterococci have been implicated in persistent root canal infections but their role in the infection process remains unclear. This study investigated the virulence, phenotype and genotype of 33 endodontic enterococcal isolates. METHODS: Phenotypic tests were conducted for antibiotic resistance, clumping response to pheromone, and production of gelatinase, hemolysin and bacteriocin. Genotype analysis involved polymerase chain reaction amplification of virulence determinants encoding aggregation substances asa and asa373, cytolysin activator cylA, gelatinase gelE, gelatinase-negative phenotype ef1841/fsrC, adherence factors esp and ace, and endocarditis antigen efaA. Physical DNA characterization involved pulsed-field gel electrophoresis of genomic DNA, and plasmid analysis. RESULTS: Potential virulence traits expressed included production of gelatinase by Enterococcus faecalis (n=23), and response to pheromones in E. faecalis culture filtrate (n=16). Fourteen strains produced bacteriocin. Five strains were resistant to tetracycline and one to gentamicin, whereas all were susceptible to ampicillin, benzylpenicillin, chloramphenicol, erythromycin, fusidic acid, kanamycin, rifampin, streptomycin and vancomycin. Polymerase chain reaction products encoding efaA, ace, and asa were detected in all isolates; esp was detected in 20 isolates, cylA in six isolates, but asa373 was never detected. The gelatinase gene (gelE) was detected in all isolates of E. faecalis (n=31) but not in Enterococcus faecium (n=2); a 23.9 kb deletion sequence corresponding to the gelatinase-negative phenotype was detected in six of the eight E. faecalis isolates that did not produce gelatinase. Pulsed-field gel electrophoresis and plasmid analyses revealed genetic polymorphism with clonal types evident. Plasmid DNA was detected in 25 strains, with up to four plasmids per strain and a similar (5.1 kb) plasmid occurring in 16 isolates. CONCLUSIONS: Phenotypic and genotypic evidence of potential virulence factors were identified in endodontic Enterococcus spp., specifically production of gelatinase and response to pheromones.     

Phenotypic and genotypic identification of enterococci isolated from canals of root-filled teeth with periapical lesions

The objectives of the present study were to identify enterococcal species isolated from the canals of root-filled teeth with periapical lesions using biochemical and molecular techniques, and to investigate the genetic diversity of the isolates. Twenty-two Enterococcus strains, isolated from the canals of root-filled teeth with persisting periapical lesions, were identified to species level using rapid ID 32 STREP galleries and partial 16S rDNA sequencing. To subtype the strains, genomic DNA from the isolates was analyzed by pulsed field gel electrophoresis (PFGE) after digestion with SmaI. Intragenic regions of two genes, ace and salA, were sequenced for further differentiation of the isolates. All strains were identified as Enterococcus faecalis by both commercial kit and partial 16S rDNA sequencing. PFGE with SmaI of 22 isolates demonstrated 18 macrorestriction profiles, whereas 13 distinct genotypes were identified after analysis of the ace and salA composite sequences. Most of the isolates from distinct patients had different PFGE profiles. Moreover, in two cases, different E. faecalis strains were found in different root-filled teeth from the same mouth. E. faecalis was the only enterococcal species isolated from the canals of root-filled teeth with periapical lesions. Genetic heterogeneity was observed among the E. faecalis isolates following PFGE and sequence-based typing method. Furthermore, the genetic diversity within root canal strains was similar to previous reports regarding E. faecalis isolates from different clinical and geographic origins.     

Prevalence, phenotype and genotype of oral enterococci

This study investigated the prevalence, phenotype and genotype of oral enterococci. Enterococci were detected in oral rinse samples from 11% of 100 patients receiving endodontic treatment and 1% of 100 dental students with no history of endodontic treatment ( P  = 0.0027). All enterococcal isolates were identified as Enterococcus faecalis . Viable counts ranged from 1 × 10 to 6 × 10³ colony forming units per mL of oral rinse sample. Potential virulence traits expressed by oral E. faecalis strains included production of hemolysin ( n  = 4) and gelatinase ( n  = 4), and response to pheromones in E. faecalis culture filtrate ( n  = 1). Six strains produced bacteriocin. All strains were susceptible to ampicillin, benzylpenicillin, gentamicin and vancomycin. There was no evidence of metal-ion resistance. One isolate produced hemolysin, gelatinase and bacteriocin, was resistant to several antibiotics, and responded to the pheromone cPD1. Pulsed-field gel electrophoresis and plasmid analysis showed that oral E. faecalis exhibited widespread genetic polymorphism, with plasmids detected in seven strains.     

Antimicrobial profiles of periodontal pathogens isolated from periodontitis patients in The Netherlands and Spain

BACKGROUND AND AIM: Antimicrobial resistance of periodontal pathogens towards currently used antibiotics in periodontics has been investigated in a previous study. Microbial resistance in the periodontal microflora was more frequently observed in Spanish patients in comparison with Dutch patients. The aim of the present study was to compare antimicrobial susceptibility profiles of five periodontal bacteria isolated from periodontitis patients in Spain and in The Netherlands. MATERIAL AND METHODS: Subgingival plaque samples from adult patients with periodontitis were collected and cultured on selective and non-selective plates. Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia, Fusobacterium nucleatum and Micromonas micros were isolated and used for minimal inhibitory concentration tests using the Epsilometer (E-test) technique. Eight different antibiotics were tested on all bacterial isolates. MIC50 and MIC90 values for each antibiotic and each species were determined and the percentage of resistant strains was calculated. RESULTS: Significantly higher MIC values were noted in Spanish strains of F. nucleatum for penicillin, ciprofloxacin, of P. intermedia for penicillin, amoxicillin and tetracycline, of M. micros for tetracycline, amoxicillin and azithromycin, and of P. gingivalis for tetracycline and ciprofloxacin. Based on breakpoint concentrations, a higher number of resistant strains in Spain were found in F. nucleatum for penicillin, amoxicillin and metronidazole, in Prevotella intermedia for tetracycline and amoxicillin, and in A. actinomycetemcomitans for amoxicillin and azithromycin. Resistance of P. gingivalis strains was not observed for any of the antibiotics tested both in Spain and The Netherlands. CONCLUSIONS: Differences exist in the susceptibility profiles of periodontal pathogens isolated from periodontitis patients in Spain and in The Netherlands. This implicates that antibiotic susceptibility testing is necessary to determine efficacy of antimicrobial agents. Also, clinical studies with antibiotics should take these differences into account. The information from the present study indicates that it may not be possible to develop uniform protocols for usage of antibiotics in the treatment of severe periodontitis in the European Union.     

Antibiotic susceptibility of anaerobic bacteria from the human oral cavity

Anaerobic, agar-dilution, minimal inhibitory concentrations (MICs) of 18 antibiotics are given for the numerically important bacterial groups from the human oral cavity. Strains are divided into susceptibility categories using the guidelines for interpretation of MICs suggested by the National Committee for Clinical Laboratory Standards. These guidelines are based on data on antibiotic concentrations attainable in serum following various dosage regimens. MICs are also compared with attainable gingival fluid levels where these are known. The highest percentages of strains were susceptible to tetracycline, with 89% of the 139 strains tested susceptible to serum levels and 97% conditionally susceptible to attainable gingival fluid levels. Ninety-eight percent of strains were conditionally susceptible to attainable gingival fluid levels of minocycline, but many strains, including Actinobacillus actinomycetemcomitans, were only moderately susceptible to attainable serum levels of this tetracycline analogue. Carbenicillin was effective against most groups of organisms, with the important exception of A. actinomycetemcomitans, at serum levels attainable with oral formulations of carbenicillin. Only 2% of the total strains tested were resistant to penicillin, while 33% of strains were categorized as moderately susceptible. Clindamycin was active against many strains of Gram-negative bacteria but was not active against A. actinomycetemcomitans, some Bacteroides, Eikenella corrodens, or the anaerobic vibrios. Metronidazole was active against A. actinomycetemcomitans, all five groups of oral Bacteroides tested, and against Capnocytophaga species. Chloramphenicol was active against A. actinomycetemcomitans, but not against most of the other groups of oral organisms. Nearly all groups contained strains non-susceptible to serum levels attainable with the usual doses of erythromycin, spiramycin, vancomycin, kanamycin, neomycin, streptomycin, doxycycline, oxytetracycline, or chlortetracycline; several strains were resistant to maximum attainable serum levels of each of these antibiotics except doxycycline.     

Antibiotic susceptibility of cocultures in polymicrobial infections such as peri-implantitis or periodontitis: an in vitro model

Background: Although polymicrobial infections, such as peri‐implantitis or periodontitis, were postulated in the literature to be caused by synergistic effects of bacteria, these effects remain unclear looking at antibiotic susceptibility. The aim of this study is to compare the antibiotic susceptibilities of pure cultures and definite cocultures. Methods: Laboratory strains of Aggregatibacter actinomycetemcomitans (Aa) (previously Actinobacillus actinomycetemcomitans), Capnocytophaga ochracea (Co), and Parvimonas micra (Pm) (previously Peptostreptococcus micros) were cultivated under anaerobic conditions, and their susceptibilities to 10 antibiotics (benzylpenicillin G, ampicillin, amoxicillin, ampicillin/sulbactam, amoxicillin/clavulanic acid, minocycline, metronidazole, linezolid, azithromycin, and moxifloxacin) were tested using the Epsilometertest. Cocultures, each consisting of two or three bacteria, were treated analogously. Results: All four cocultures showed lower susceptibilities to azithromycin and minocycline than to pure cultures. The coculture Aa‐Co showed a lower susceptibility to moxifloxacin as did the coculture Aa‐Pm to benzylpenicillin G; the coculture Co‐Pm showed a lower susceptibility to amoxicillin, amoxicillin/clavulanic acid, metronidazole, and benzylpenicillin G. However, the coculture Co‐Pm showed a higher susceptibility to ampicillin, linezolid and moxifloxacin as did Aa‐Pm and Aa‐Co‐Pm to linezolid. Conclusions: In addition to established in vitro assays, it was demonstrated that antimicrobial cocultures caused antibiotic susceptibilities that differed from those of pure cultures. Bacterial cocultures frequently showed lowered susceptibilities to antibiotics.     

Resistance profile survey of 50 periodontal strains of Actinobacillus actinomyectomcomitans.

BACKGROUND: Antibiotic resistance has been increasingly described among bacterial species colonizing periodontal pockets, particularly in Prevotella and Porphyromonas spp. strains producing beta-lactamases, and frequently associated with resistance to tetracycline and erythromycin. These resistance genes may be carried on motile genetic elements, or transposons, capable of interspecies and intergeneric transmission among bacterial strains colonizing a same ecological niche. The aim of this prospective study was to determine the resistance profile of Actinobacillus actinomycetemcomitans and the prevalence of A. actinomycetemcomitans strains producing beta-lactamases in periodontal pockets. METHODS: Fifty strains of A. actinomycetemcomitans were isolated from 42 patients with adult periodontitis. No patient had periodontal or antibiotic therapy in the previous 6 months. Bacterial samples were collected from periodontal pockets > or =5 mm, appropriately diluted, inoculated onto selective medium (chocolate blood agar with bacitracin 75 microg/ml and vancomycin 5 microm/ml) and incubated for 5 days at 37 degrees C in air with 5% CO2. After conventional identification, susceptibility testing to 11 antibiotics was performed by the broth dilution method, in trypticase soy broth supplemented with yeast extract, hemin, and 0.1% NaHCO3 to maintain microaerophilic conditions in the microtitration plate wells by CO2 formation. RESULTS: No strain demonstrated resistance to amoxicillin, amoxicillin-clavulanic acid combination, pristinamycin, or ciprofloxacin at the breakpoint, but 40% of the strains were slightly resistant to penicillin G, and 4% were resistant to erythromycin, 90% to spiramycin, 18% to clarythromycin, 4% to tetracycline, 72% to metronidazole, and 12% to ornidazole. Amoxicillin, followed by tetracycline and erythromycin, was the most effective antibiotic on A. actinomycetemcomitans. The phenotypic research of a beta-lactamase was negative for all the strains tested. CONCLUSIONS: In this work, most A. actinomycetemcomitans strains were resistant to metronidazole, but the amoxicillin-metronidazole association may be of interest against subgingival anaerobic and capnophilic mixed flora. Pristinamycin and ciprofloxacin appeared as effective alternative monotherapies against A. actinomycetemcomitans. The threat of beta-lactam antibiotic resistance related to beta-lactamase production is currently not a problem with A. actinomycetemcomitans as it has been reported in oral anaerobes.     

Antibiotic Susceptibility of Periodontal Enterococcus faecalis

Background: Enterococcus faecalis may contribute to periodontal breakdown in heavily infected subgingival sites, particularly in patients responding poorly to mechanical forms of periodontal therapy. Because only limited data are available on the antimicrobial sensitivity of enterococci of subgingival origin, this study evaluates the in vitro antibiotic susceptibility of E. faecalis isolated from periodontitis patients in the United States. Methods: Pure cultures of 47 subgingival E. faecalis clinical isolates were each inoculated onto specially prepared broth microdilution susceptibility panels containing vancomycin, teicoplanin, and six oral antibiotics of potential use in periodontal therapy. After incubation in ambient air for 18 to 20 hours, minimal inhibitory drug concentrations were determined using applicable Clinical and Laboratory Standards Institute criteria and interpretative guidelines. The organisms were additionally evaluated for in vitro resistance to metronidazole at 4 μg/mL. Results: Periodontal E. faecalis exhibited substantial in vitro resistance to tetracycline (53.2% resistant), erythromycin (80.8% resistant or intermediate resistant), clindamycin (100% resistant to 2 μg/mL), and metronidazole (100% resistant to 4 μg/mL). In comparison, the clinical isolates were generally sensitive to ciprofloxacin (89.4% susceptible; 10.6% intermediate resistant) and 100% susceptible in vitro to ampicillin, amoxicillin/clavulanate, vancomycin, and teicoplanin. Conclusions: Tetracycline, erythromycin, clindamycin, and metronidazole revealed poor in vitro activity against human subgingival E. faecalis clinical isolates, and would likely be ineffective therapeutic agents against these species in periodontal pockets. Among orally administered antibiotics, ampicillin, amoxicillin/clavulanate, and ciprofloxacin exhibited marked in vitro inhibitory activity against periodontal E. faecalis, and may be clinically useful in treatment of periodontal infections involving enterococci.     

Susceptibility of Porphyromonas gingivalis in biofilms to amoxicillin,doxycycline and metronidazole

The susceptibility of Porphyromonas gingivalis to amoxicillin, doxycycline and metronidazole was determined by a standardized method taking into account the biofilm mode of growth of subgingival bacteria. The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of 48-h biofilms of P. gingivalis established on membrane filters in a Modified Robbins Device were determined by agar dilution. The results were compared to (i) conventional MIC determinations, (ii) the susceptibility of planktonic cultures with cell numbers equal to those of the biofilms, and (iii) results for detached biofilm cells. The MICs of the biofilms of the six reference strains and clinical isolates containing 107-8 cells/filter were much higher than the conventional MIC values. However, the MIC of planktonic cultures of equal cell numbers also increased, indicating that an inoculum effect is part of the explanation of the increased resistance of biofilms. Still, the MBCs of biofilms were 2-8 times, and those for doxycycline up to 64 times, greater than the MBC values for planktonic cultures.     

A preliminary study investigating the survival of tetracycline resistant Enterococcus faecalis after root canal irrigation with high concentrations of tetracycline

AIM: To compare the ability of two Enterococcus faecalis strains to survive exposure to an irrigation solution containing a high concentration of tetracycline in the root canals of bovine teeth. METHODOLOGY: The root canals of twelve bovine incisor root sections were chemo-mechanically prepared using commercially available drills, sodium hypochlorite and ethylenediamine tetra-acetic acid. The root sections were divided into two groups and inoculated with either a tetracycline sensitive or resistant strain of E. faecalis. The strains are isogenic, however one contains a conjugative transposon related to Tn916 which confers resistance to tetracycline, and the other strain is sensitive to the antibiotic. After 26 days of incubation the root canals were irrigated using one of three solutions (sterile distilled water, 50% ethanol or tetracycline at a concentration of 30 mg mL(-1)). The roots were sampled by grinding dentine and canal contents and the debris collected were incubated in broth to assess growth. RESULTS: Irrigation with sterile distilled water or 50% ethanol did not remove all of the cells present. The tetracycline containing solution was efficient in preventing any growth of sensitive E. faecalis, however the resistant strain was able to survive a 5 min exposure at 30 mg mL(-1). CONCLUSIONS: The presence of the Tn916-like conjugative transposon containing the tetracycline resistance gene tet(M) allowed an E. faecalis strain to survive irrigation using a solution containing an extremely high concentration of tetracycline in a root canal model.     

Susceptibility of some oral microorganisms to chlorhexidine and paramonochlorophenol

Since the use of antimicrobial agents is required in endodontic therapies, this study aimed at determining the minimum inhibitory concentrations (MICs) of chlorhexidine digluconate and paramonochlorophenol (PMC) against microorganisms commonly found in endodontic infections. Both agents were tested by agar dilution tests against Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Candida albicans, Prevotella intermedia, Porphyromonas gingivalis, Porphyromonas endodontalis, Prevotella denticola and Prevotella melaninogenica. The MIC of chlorhexidine ranged from 2.67 to 80.00 microg/ml, and the MIC of PMC from 46.67 to 213.33 microg/ml. The highest MIC value of PMC was detected for E. faecalis whereas E. coli was the most susceptible microorganism to this agent. The highest MIC values of chlorhexidine were observed for P. aeruginosa whereas E. coli and P. denticola were the most susceptible microorganisms to this agent. Since the MIC values observed are much lower than the concentrations currently used in the endodontic therapy, it is suggested that both agents are effective in reducing the microbiota in the root canal.     

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.     

Susceptibility of Porphyromonas gingivalis in biofilms to amoxicillin,doxycycline and metronidazole

The susceptibility of Porphyromonas gingivalis to amoxicillin, doxycycline and metronidazole was determined by a standardized method taking into account the biofilm mode of growth of subgingival bacteria. The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of 48‐h biofilms of P. gingivalis established on membrane filters in a Modified Robbins Device were determined by agar dilution. The results were compared to (i) conventional MIC determinations, (ii) the susceptibility of planktonic cultures with cell numbers equal to those of the biofilms, and (iii) results for detached biofilm cells. The MICs of the biofilms of the six reference strains and clinical isolates containing 10^7?8 cells/filter were much higher than the conventional MIC values. However, the MIC of planktonic cultures of equal cell numbers also increased, indicating that an inoculum effect is part of the explanation of the increased resistance of biofilms. Still, the MBCs of biofilms were 2–8 times, and those for doxycycline up to 64 times, greater than the MBC values for planktonic cultures.     

Microbiological analysis of infected root canals from symptomatic and asymptomatic teeth with periapical periodontitis and the antimicrobial susceptibility of some isolated anaerobic bacteria

The purpose of the present study was to investigate the correlation between the composition of the bacterial flora isolated from infected root canals of teeth with apical periodontitis with the presence of clinical signs and symptoms, and to test the antibiotic susceptibility of five anaerobic bacteria mostly commonly found in the root canals of symptomatic teeth against various substances using the E-test. Microbial samples were taken from 48 root canals, 29 symptomatic and 19 asymptomatic, using adequate techniques. A total of 218 cultivable isolates were recovered from 48 different microbial species and 19 different genera. Root canals from symptomatic teeth harbored more obligate anaerobes and a bigger number of bacterial species than the asymptomatic teeth. More than 70% of the bacterial isolates were strict anaerobes. Statistical analysis used a Pearson Chi-squared test or a one-sided Fisher's Exact test as appropriate. Suggested relationships were found between specific microorganisms, especially gram-negative anaerobes, and the presence of spontaneous or previous pain, tenderness to percussion, pain on palpation and swelling amoxicillin, amoxicillin + clavulanate and cephaclor were effective against all the strains tested. The lowest susceptibility rate was presented by Prevotella intermedia/nigrescens against Penicillin G. Our results suggested that specific bacteria are associated with endodontic symptoms of infected teeth with periapical periodontitis and the majority of the anaerobic bacterial species tested were susceptible to all antibiotics studied.