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

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

In vitroantimicrobial effect of chlorhexidine-impregnated gutta percha points onEnterococcus faecalis

AIM

To evaluate the in vitro antimicrobial effect of chlorhexidine-impregnated gutta percha points, Roeko activ point (Roeko, Langenau, Germany) on Enterococcus faecalis.

METHODOLOGY

Human maxillary premolar roots were prepared with.04 rotary ProFile instruments to a master apical file size 40, autoclave-sterilized and then infected with E. faecalis (ATCC 29212) for 3 weeks. Baseline controls were carried out verifying negligible effects of plain gutta percha cones on E. faecalis. Subsequent to intracanal placement of calcium hydroxide, 'activ points' or saline (positive control) and the 2-week incubation in 54 root specimens, dentine sampling at depths of 100 and 250 micro m was carried out using.04 rotary ProFile instruments at sizes 60 and 90 to assess the quantity of bacteria present. Inactivating agents were used prior to sampling and the colony-forming units (CFU) of E. faecalis were then plate-counted after culturing. Statistical analysis was completed using the paired t-test.

RESULTS

In comparison to the positive control, treatment with calcium hydroxide (P = 0.000 and 0.000) or activ points (P = 0.000 and 0.002) produced significantly lower colony counts of E. faecalis at dentine depths of 100 and 250 micro m, respectively. Calcium hydroxide (2.10 x 102 CFU mL-1) was significantly more effective than activ points (1.58 x 103 CFU mL-1) at 100 micro m (P = 0.013), but not at 250 micro m (P = 0.353). Neither of these two medications was able to eliminate E. faecalis completely.

CONCLUSIONS

Chlorhexidine-impregnated activ points did not possess an in vitro inhibitory activity strong enough to eliminate E. faecalis completely from infected dentinal tubules.

Cytolethal distending toxin of Actinobacillus actinomycetemcomitans. Occurrence and association with periodontal disease

The cytolethal distending toxin (Cdt) of Actinobacillus actinomycetemcomitans, a periodontal pathogen, is a newly described cytotoxin with immunosuppressive properties, capable of causing cell cycle arrest of lymphocytes. The objectives of this study were to investigate the occurrence of A. actinomycetemcomitans with the cdt genotype in the subgingival plaque of periodontitis patients and to determine the association of this bacterial genotype with periodontal disease. A total of 146 subgingival plaque samples from periodontitis patients were assayed by the PCR method using oligonucleotide primers targeting the cdt operon of A. actinomycetemcomitans. Primers targeting the leukotoxin gene A (ltxA) of A. actinomycetemcomitans was used to determine the occurrence of the bacteria in the plaque samples at baseline. At baseline, A. actinomycetemcomitans was detected in 106 out of 146 (73%) diseased sites studied. Among the 106 diseased sites found to harbor A. actinomycetemcomitans, 13 sites were positive for the bacteria with the cdt genotype (12%). Out of the 13 positive sites, 10 sites were obtained from patients diagnosed with aggressive periodontitis (77%). Thus, A. actinomycetemcomitans with the cdt genetic subtype has low occurrence in the subgingival plaque of periodontitis patients. However, a strong association was observed between the presence of the bacteria and aggressive forms of periodontitis. Thus, the cytotoxic and immunosuppressive properties of A. actinomycetemcomitans Cdt may function to cripple the host immunity and contribute to the pathogenesis of aggressive periodontitis.

ADP-ribosylating binary toxin genes of Clostridium difficile strain CCUG 20309

The cdt genes that encode a binary ADP-ribosylating toxin in Clostridium difficile were first characterized from a toxigenic C. difficile strain CD196 in 1997. We report here C. difficile strain CCUG 20309 (ATCC 8864), a strain that produces toxin B but not toxin A, also carry a complete set of cdtA and cdtB genes. These genes were sequenced by cycle sequencing method. The 2 ORFs and the intergenic sequences of these 2 strains have a homology of 99.6%. Interestingly, 9 extra bases were found within the cdtA gene of strain CCUG 20309 which do not affect the downstream region of the ORF. Using the same homologous primers, the highly toxigenic reference strain VPI 10463 was found to carry only parts of the 2 ORFs while a nontoxigenic strain ATCC 8884 does not carry any of the cdt genes. Though it remains to be determined whether these genes are expressed, it is significant that strain CCUG 20309 contains the complete set of cdt genes. We speculate that the putative expressed proteins may contribute to pathogenesis, for example, enterotoxicity, of this unique strain of bacteria.

Bacteroides forsythus prtH genotype in periodontitis patients: occurrence and association with periodontal disease

Bacteroides forsythus has been described as a periodontopathogen and its presence in the subgingival plaque can lead to periodontal disease. Recently, a cysteine protease designated as prtH was isolated and characterized from B. forsythus ATCC 43037. The purpose of this study was to determine the prevalence and the association of the prtH gene of B. forsythus with periodontal disease. A total of 160 subgingival plaque samples were assayed with the polymerase chain reaction method using oligonucleotide primers targeting the prtH and the 16S rDNA genes of B. forsythus. Primers targeting the 16S rDNA gene of B. forsythus were used to determine the occurrence of the bacteria in the subgingival plaque samples at baseline. At baseline, B. forsythus was detected in 78 out of 86 (91%) diseased sites and 33 out of 74 (45%) healthy sites studied. Among the 86 diseased sites examined, 73 sites (85%) were colonized by the bacteria with the prtH genotype. In sites of the periodontally healthy, 7 out of 73 (10%) possessed B. forsythus with the prtH genotype. The results obtained suggested strong association of the prtH gene of B. forsythus with adult periodontitis. Although this bacterial species was detected from about half of the periodontally healthy samples, only a fraction of these subjects possess the bacteria strain with the prtH genetic subtype. We propose the use of the prtH gene as an alternative to the more widely used 16S rDNA gene of B. forsythus, for a more accurate determination of the prevalence of periodontal health and disease in epidemiological studies and clinical screening.

Prevalence of Actinobacillus actinomycetemcomitans in an ethnic adult Chinese population

AIM

The aim of this study was to determine the prevalence and the structure of the leukotoxin promoter region of Actinobacillus actinomycetemcomitans in an ethnic Chinese population.

METHOD

Subgingival plaque samples were collected from 42 patients with moderate to advanced periodontitis and 50 periodontally healthy patients. A. actinomycetemcomitans was detected directly from the crude subgingival plaque by PCR using leukotoxin gene specific primers. The presence of A. actinomycetemcomitans was determined by a single 285 bp PCR amplicon.

RESULTS

A. actinomycetemcomitans was found to be present in the subgingival plaque of 68 out of a total of 92 patients examined (74%). 29 out of the 42 periodontitis patients tested were carriers of A. actinomycetemcomitans (69%). Among the periodontally healthy patients studied, 39 out of 50 subjects possessed the bacteria (78%). PCR analysis of the promoter region of the ltx operon revealed that none of the 42 moderate to advanced periodontitis patients examined harboured A. actinomycetemcomitans strains with the JP2-like promoter of the ltx operon, known to enhance leukotoxin expression. 2 out of the 27 advanced periodontitis patients clinically diagnosed as suffering from rapidly progressive periodontitis were found to be carriers of the mildly toxic strain of A. actinomycetemcomitans with the characteristic 652-like promoter.

CONCLUSIONS

The high prevalence of A. actinomycetemcomitans, regardless of whether the subgingival samples were analysed from patients with healthy or diseased periodontium suggests that this bacterial species is part of the normal oral flora of ethnic Chinese. Our preliminary results also suggested that subjects who harboured the mildly toxic strain of A. actinomycetemcomitans were potentially susceptible to aggressive forms of periodontitis.

Rapid identification of Pseudomonas aeruginosa from ocular isolates by PCR using exotoxin A-specific primers

The purpose of this research was to evaluate the use of PCR for the identification of ocular isolates of Pseudomonas aeruginosa by using primers specific to the exotoxin A gene of the bacteria. Genomic DNA was obtained from ocular microbial isolates of keratitis patients. Primers were designed based on the published sequence of the exotoxin A gene of P. aeruginosa. Using the primers designed, PCR reactions were performed on the DNA samples. The PCR was also examined for its specificity and sensitivity. In addition, a direct PCR using heating method was attempted on P. aeruginosa with no separate DNA extraction step. ATCC strains of P. aeruginosa were included as positive controls. The rest of the bacteria other than P. aeruginosa served as negative controls. A single band was obtained when analysed on agarose gel electrophoresis only from samples that contained genomic DNA of P. aeruginosa. The direct PCR method was also successful with the same band produced from the amplification. The whole process was completed within 4 h. The direct PCR amplification targeting at the exotoxin A gene of P. aeruginosa is potentially a rapid, specific, sensitive and relatively simple method for the identification of ocular isolates of P. aeruginosa.

Sequence analysis of a new open reading frame located in the pathogenicity locus of Clostridium difficile strain 8864

Strain 8864 is a natural isolate of Clostridium difficile that is toxin B-positive and toxin A-negative. Recent work showed that there is a genetic rearrangement occurring at the pathogenicity locus (PaLoc) of the bacteria. Our investigation in the PaLoc region revealed an open reading frame (tcdF) of 543 bp DNA not reported before. This tcdF could encode a putative polypeptide of 22 kDa. Although no peptide homology was found with other known proteins, we postulate that it could be a novel protein because not only highly consensus ribosome-binding and promoter sequences were found upstream of tcdF, transcript was also identified at the region occupied by tcdF.

Nucleotide and peptide sequences of the open reading frame encoding a truncated toxin A gene of Clostridium difficile strain CCUG 20309

The open reading frame encoding a putative truncated toxin A gene of Clostridium difficile in strain CCUG 20309 (ATCC 8864), a strain that produces toxin B but not toxin A, was sequenced by cycle sequencing method. The coding region contains 2097 base pairs and has a GC content of 26.4%. The deduced polypeptide is 50 kDa and is generally hydrophilic. Although strain CCUG 20309 of C. difficile was reported not to produce toxin A, it is enterotoxic, an inherent property of toxin A in pathogenic strains of C. difficile. It therefore remains to be determined whether a truncated form of toxin A could actually be expressed from the open reading frame by this strain of C. difficile.

The enzymatic domain of Clostridium difficile toxin A is located within its N-terminal region

Clostridium difficile, an anaerobic pathogen encountered in human enteric disease, produces two major virulence factors, toxins A and B, which are members of a clostridial family of large cytotoxins. These are glucosyltransferases, which use a UDP-sugar as co-substrate to glucosylate and inactivate small GTPases of the Rho or Ras families, culminating in cytotoxicity. Clinically, toxin A is perhaps the most important family member, because it causes major tissue damage in the course of disease, leading to a potentially lethal, pseudomembranous colitis. The location of the enzymatic domain of toxin A and mechanistic details of its action are not yet known, so we wished to localize this domain using gene deletion constructions from the full-length gene and by monitoring glucosylation activity of encoded protein products. Toxin A deletions were obtained by successively truncating the C-terminal coding region. These were transformed into E. coli, cell lysates were prepared and they were assayed for their ability to glucosylate Rho A protein, using an in vitro enzymatic assay. We report that the UDP-glucose binding site, the catalytic site for glucose transfer and the Rho A interaction site occur within the first 659 N-terminal amino acids of toxin A, i.e., less than 25% of the length of holotoxin A. Localization of the enzymatic domain of toxin A to these 659 N-terminal amino acids should greatly simplify studies on mechanistic details of this clinically important toxin.

Molecular analysis of the promoter region of the Clostridium difficile toxin B gene that is functional in Escherichia coli

Clostridium difficile is a human pathogen that produces two types of toxins, A and B, that cause a potentially lethal gastrointestinal syndrome termed pseudomembranous colitis. Virtually nothing is known about the mechanism of regulation of toxin production in this organism, and cis-regulatory regions of neither toxin have yet been identified, thus prompting this investigation. A motif homologous with the Shine-Dalgarno sequence of Escherichia coli occurs upstream from the putative initiation codon of toxin B, making this region also a candidate to contain a promoter. Therefore, a subgenomic DNA library of C. difficile in a plasmid vector was first constructed encompassing the 5'-end of the toxin B gene. A 450-bp DNA fragment was excised from the subgenomic DNA library clone and subcloned into a promoter-probe plasmid vector that contains two divergently oriented, promoterless genes to assay for promoter function. This subcloned DNA fragment directed the expression of alkaline phosphatase, a reporter gene product of the promoterless vector, thus indicating the presence of a functional promoter. To locate the promoter more precisely, a series of nested deletions of the toxin B promoter subclone was constructed with exonuclease III. The promoter that facilitates expression of the toxin B gene in E. coli was localised, based on alkaline phosphatase activity. The transcriptional initiation site of toxin B mRNA in E. coli was mapped by primer extension analysis, suggesting two closely associated tandem start sites directed by two similarly spaced promoters within this localised region.