Clonality of Fusobacterium nucleatum in root canal infections

Fusobacterium nucleatum is a gram-negative non-spore-forming, non-motile, obligate anaerobic rod that is normally isolated from the oral cavity. Several studies have reported a significant heterogeneity within the F. nucleatum species. The aim of the present study was to analyze the clonal diversity of F. nucleatum strains isolated from intracanal infections and to evaluate the presence of Enterobacterial Repetitive Intergenic Consensus (ERIC)-like sequences in the genome of F. nucleatum. Samples were collected from 13 single-root teeth from adult patients, all having carious lesions, necrotic pulps and radiographic evidence of periradicular bone loss. F. nucleatum was isolated from two different patients (subjects 5 and 7) by culture. Amplification of 19 colonies from subject 5 and 15 colonies from subject 7 using ERIC primers resulted in four clonal types, two per subject. An intense amplicon of approximately 700 bp was generated by ERIC-PCR for all F. nucleatum isolates and F. nucleatum ssp. polymorphum ATCC 10953. The amplification reaction using primer 1254 confirmed the results obtained with the ERIC primer. Our findings indicate that DNA fingerprints provided by ERIC- and Arbitrarily Primed (AP)-PCR may constitute a powerful tool for investigating F. nucleatum clonal diversity.

Direct amplification of rRNA gene sequences for identification of selected oral pathogens in root canal infections

AIM

The purpose of this study was to assess the prevalence of selected oral pathogens in root canal infections and their relationship with symptoms using a highly sensitive technique, the polymerase chain reaction.

METHODOLOGY

Samples were obtained from 91 infected teeth associated with periradicular lesions, including cases of acute periradicular abscesses. DNA was extracted from the samples and analysed for the presence of target microbial species using a PCR-based identification assay.

RESULTS

All samples were positive for the presence of bacteria. Streptococcus anginosus group was detected in 16.7%, Fusobacterium nucleatum in 14.3%, and Bacteroides forsythus in 7.1% of the abscess samples. No pus sample yielded Actinomyces israelii, Actinobacillus actinomycetemcomitans or fungal species. In general, B. forsythus was found in 20% of the cases (16 of 80), S. anginosus in 12% (6 of 50), F. nucleatum in 10% (6 of 60) and A. israelii in 5% (two of 40). A. actinomycetemcomitans was not detected in any case. Fungi were present in only one of 50 cases (2%). There was no correlation between the species and symptoms.

CONCLUSIONS

Direct molecular approaches appear to be a valuable tool for the rapid and reliable diagnosis of infectious diseases, as well as for research purposes. There was no correlation between target microbial species and symptoms.

Antimicrobial activity and flow rate of newer and established root canal sealers

Endodontic sealers that possess both optimum flow ability and antimicrobial properties may theoretically assist in the elimination of microorganisms located in confined areas of the root canal system. The antimicrobial effects and the flow rate of the following sealers were investigated and compared: Kerr Pulp Canal Sealer EWT, Grossman's Sealer, ThermaSeal, Sealer 26, AH Plus, and Sealer Plus. The agar diffusion test was used to assess the antimicrobial activity of the sealers. In the flow assay, the sealers were placed between two glass slabs and a weight of 500 g was placed on the top of the glass. The diameters of the formed discs were recorded. All root canal sealers tested showed some antimicrobial activity against most of the microorganisms. There were no significant differences between the materials tested (p > 0.05). All root canal sealers also flowed under the conditions of this study. Statistical analysis of the results revealed that AH Plus and Kerr Pulp Canal Sealer EWT had flow values significantly superior to the other sealers tested (p > 0.05). Taken together, these findings suggest that these sealers have the potential to help in the microbial control in the root canal system.

Use of rep-PCR to define genetic relatedness among Bacteroides fragilis strains

Bacteroides fragilis, a component of the normal flora and an important anaerobic pathogen in non-intestinal endogenous infections, has recently been associated with enteric diseases. In this study, 41 B. fragilis strains were analysed in relation to their genetic diversity. This collection included two reference strains (ATCC 23745 and 25285), 20 isolates from non-intestinal infections, six from intestinal infections, five from intestinal microflora and eight from an aquatic environment. The fingerprints were generated by using two repetitive sequences (REP and ERIC) as primers to PCR (rep-PCR). A dendrogram was obtained with the Taxotron Program. Three clusters (threshold genotypes I, II and III) were observed when the genetic distance was 0.30. These results confirm previous data found regarding the genotypical diversity of B. fragilis.

Expression of Bacteroides fragilis virulence markers in vitro

Bacteroides fragilis isolates from intestinal and non-intestinal infections, normal flora and the environment were examined for properties linked with interactions among cells in vitro. Different adhesion molecules were detected in agglutination assays with human erythrocytes and tests for auto-agglutination and adherence to human colon carcinoma cells (HT29). There was no correlation between these properties, indicating that independent molecules are involved. Treatment with trypsin, heat or EDTA inhibited agglutination and adherence, suggesting that these molecules are proteins. The lack of correlation with the origin of the strains did not permit any of these activities to be recognised as virulence markers. The expression of fragilysin, a protease associated with damage to intestinal cells and bacterial translocation, was examined. Only those strains from patients with diarrhoea expressed this protease activity in assays with HT29 cells and this was confirmed by specific PCR for the bft gene. The activity of fragilysin as an enterotoxin was confirmed in the rabbit intestinal ligated loop assay. The association of this property only with strains from intestinal infections indicates that it is too early to suggest this protease as a determinant factor of B. fragilis invasiveness.

Bacteroides fragilis isolates compared by AP-PCR

Bacteroides fragilis is a component of the normal intestinal flora and an important pathogen in nonintestinal endogenous infections. It has been associated with enteric infections and has already been detected in polluted water. In order to evaluate the genetic diversity of B. fragilis, a total of 31 isolates and two reference strains were examined. This collection included strains from nonintestinal infections [12], intestinal infections [5], intestinal microflora [10], aquatic environments [4], and the reference strains ATCC 25285 and ATCC 23745. DNA fingerprints were detected using two separate PCR reactions with different arbitrary primers. The computer-assisted system Taxotron (Institut Pasteur, Dr P. Grimont) was used to analyze the profiles obtained and dendrograms were generated. By using a distance of 0.65 as the threshold, two clusters (hereafter referred to as genotypes I and II) were defined. Strains of differents origins could be distributed into both genotypes. We were unable to detect any obvious correlation between a given genotype and the specific disease or the source of the corresponding strains.

Electrophoretic characterization of exposed outer membrane proteins in environmental and human Bacteroides fragilis strains

Bacteriodes fragilis isolated from aquatic environment, from infectious process and from human feces were compared as to their outer membrane protein electrophoretic profiles after staining with Coomassie blue and reacting with antibodies prepared against whole-cell antigens of a reference strain from a clinical source. A marked homogeneity was found among the strains with these methodologies. The profiles of all strains obtained after radio-iodination of the intact cell showed qualitative similarity when compared with the profiles obtained by the other methods. Thus, these data allow us to suggest the designation of the peptides observed in the autoradiograms as surface-exposed proteins. Differences observed in the autoradiograms in the expression of bands mainly detected at a molecular weight of 28 in the commensal strain 118,310 defined previously as avirulent, in addition to a distinction in the titres of agglutination with the sera tested and lower reactivity in the immunoblotting assays, suggest a relationship of the B. fragilis surface architecture with the virulence potential as well as with the origin of the strain.

Influence of stress conditions on Bacteroides fragilis survival and protein profiles

Bacteroides fragilis strains isolated from different sources, i.e. 1 strain (AA1) from an aquatic environment, 1 strain from normal flora (118310) and the type strain (ATCC 25285) originally isolated from clinical material, were analysed for both cell envelope proteins composition and surviving under oxidative stress starvation. All strains examined showed a similar survival response when cultured in drinking water with a ten-fold decrease in viable counts per day during the 7 days of analysis. The outer membrane protein (OMP) profiles of all strains were quite similar during the stress period as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). However, the periplasmic proteins of the strain 118310 showed two protein bands at 48 and 58 kDa, respectively, that were absent in the strains AA1 and ATCC 25285 during the incubation period in potable water. Whole cells and periplasmic 35S-labelled proteins from bacteria cultured in drinking water showed a significant increase in proteins at 16, 18, 24, 26, 35, 48, and 58 kDa and 18, 22, 24, 48, 58, and 70 kDa, respectively, in all strains when compared to cells grown in BHI-PRAS media as detected by autoradiography following SDS-PAGE. These data suggest that B. fragilis may have a synthesis mechanism that allows them to adapt to adverse environments.

Whole-cell and periplasmic protein banding patterns of environmental and human Bacteroides fragilis strains

In order to investigate the relationship among virulent and avirulent Bacteroides fragilis strains, SDS-PAGE of whole-cell proteins (WP) and periplasmic proteins (PP) were used to establish a protein profile of strains isolated from human infections, fecal flora and environmental water. Despite different sources of the strains, no significant differences were observed as determined by the WP SDS-PAGE analysis. In contrast, the proteins obtained from the bacterial periplasm showed differences in the electrophoretic protein profile. Two distinct PP profile patterns were obtained. Pattern A included 6 out of the 8 virulent strains and pattern B, 6 out of 8 avirulent strains. Interestingly, an environmental strain that was capable of inducing abscesses in mice, had a PP profile highly similar to that of the virulent strains from human infections. These data indicate that PP from B. fragilis may be useful to characterize differences among virulent and avirulent strains. Moreover, strains isolated from environmental water may also be a source of exogenous infections by B. fragilis.

Surface vesicles: a possible function in commensal relations of Bacteroides fragilis

Surface vesicles (SV) defined by electron microscopy as outer membrane (OM) extrusions were detected in Bacteroides fragilis strains from distinct sources. A partial identity between SV and OM electrophoretic protein profiles, in addition to the microscopic analysis, may suggest the designation of OMSV. Sialidase activity, a virulence determinant, was associated with these sub-cellular structures in all the strains, but in an inverse relation to the vesicle quantity per cell. A commensal strain, previously defined as avirulent in an animal model, presented the lowest vesicle-associated sialidase activity and the greatest SV expression as opposed to what happened with clinical and environmental strains. These results seem to suggest that these surface components have a function in commensal stages of B. fragilis.