Sortase is a newly discovered transpeptidase that covalently links LPXTGX-containing surface proteins to the gram-positive bacterial cell wall. In this study, the sortase gene (srtA) was isolated from Streptococcus mutans NG8 by PCR. The gene encoded a 246-amino-acid protein, including a 40-amino-acid signal peptide. The srtA gene was insertionally inactivated by a tetracycline resistance cassette. P1, a major surface protein adhesin previously shown to anchor to the peptidoglycan by the LPXTGX motif, was secreted into the culture medium by the srtA mutant. In contrast, the wild-type P1 remained cell wall associated. Complementation of the mutant with srtA restored the P1 surface expression phenotype. P1 produced by the mutant, but not that produced by the wild type and the srtA-complemented mutant, was recognized by an antibody raised against the hydrophobic domain and charged tail C terminal to the LPXTGX motif. These results suggest that the failure to anchor P1 to the cell wall is due to the lack of cleavage of P1 at the LPXTGX motif. The srtA mutant was markedly less hydrophobic than the wild type and the complemented mutant. The srtA mutant failed to aggregate in the presence of saliva or salivary agglutinin and adhered poorly to saliva-or salivary agglutinincoated hydroxylapatite. In rats, the srtA mutant colonized the teeth poorly when sucrose was absent. When sucrose was present, the srtA mutant colonized the teeth but less effectively and induced significantly less caries (P < 0.05) than the wild-type strain. In conclusion, the sortase enzyme in S. mutans is responsible for anchoring P1 to the cell surface and plays a role in modulating the surface properties and cariogenicity of S. mutans.The major cell surface protein P1, also known as antigen I/II (ca. 185 kDa), from Streptococcus mutans is an adhesin that interacts with a high-molecular-weight salivary agglutinin and has been implicated in the adherence of the bacterium to the tooth surface (16). Sequence analysis of the P1 gene reveals common features at the C terminus of the protein, as found in several hundreds of surface proteins from many gram-positive coccal bacteria (17). These features include a hydrophilic (wall-associated) region, a highly conserved hexapeptide LPXTGX, a hydrophobic (membrane-spanning) domain, and a charged tail (22,23).In our previous studies, we have demonstrated the requirement of the C-terminal domains in P1 surface localization in S. mutans (10, 11). Site-directed mutagenesis analysis showed that the Thr residue within the LPXTGX motif plays a crucial role in enzymatic cleavage and anchoring of P1 to the cell wall (15).A transpeptidase termed sortase (SrtA) was identified initially in Staphylococcus aureus (27) and recently in Streptococcus gordonii (5), Streptococcus suis (20), Streptococcus pyogenes (2), and Listeria monocytogenes (4, 9). The enzyme is responsible for covalently anchoring protein A to the cell wall (27) and plays a role the pathogenesis of S. aureus (12, 18). Recently, the role of SrtA in virulence...
The purpose of this study was to produce a valid scale for use in measuring the values of dental students and practitioners-the lack of which has impeded research on professionalism in dentistry. Following standard scale development procedures, we had focus groups of dental practitioners (N=23) develop a ninety-nine-item pool of value terms related to dentistry. Next, Canadian dentists (N=449) rated the relevance of each item through an online survey. They also rated the values in a generic values measure, Schwartz's Values Scale. Exploratory and conirmatory factor analyses identiied twenty-ive items representing ive values: Altruism, Personal Satisfaction, Conscientiousness, Quality of Life, and Professional Status. These values correlate with related dimensions from Schwartz's measure; they also correspond to the values in the American Dental Education Association's statement on professionalism. We then administered the new Dental Values Scale to dental students (N=96) to determine the relationship between practitioner and student values. First-year students were higher in Conscientiousness, Altruism, and Personal Satisfaction than practitioners, but these values decreased over time to those held by the dentists. We discuss the implication of these results and the potential value of the new scale for dental education.
The literature increasingly indicates that lasers will have a multitude of applications for dental hard tissue procedures, e.g. preventive therapy, caries removal, laser etching and endodontic therapy. However, it is critical that such laser therapies avoid the production of heat levels which will be damaging to the surrounding vital tissues, such as the dental pulp and periodontal tissues. Our preliminary research on temperature changes across C02 lased dentin indicated that for single preventive therapeutic exposures (1.2 W., 0. 1 sec., 1.0 mm focal spot) the mean temperature rise across 350 j.tm of dentin was 0.57 0C while across 1000 .tm of dentin the mean rise was only 0.18 °C. Further research utilizing multiple preventive therapeutic exposures (1.2 W., 0. 1 sec., 1.0 mm focal spot, 3 x 1.0 sec. intervals) showed mean temperature elevations of 1.56 0C across 350 m of dentin and 0.66 O across 1000 xm of dentin. While these temperature elevations, which would be associated with preventive therapy, are very low and would be biologically acceptable, it must be noted that exposures of higher intensities are required to fuse enamel and porcelain, or remove decay. This current research investigates temperature elevations which occuT during C02 lasing utilizing the following exposure parameters: 8.0 W., 1.0 mm focal spot, 0.1 sec. exposures, 2 or 4 exposures per site pulsed 1.0 sec. apart. Three dentin thicknesses were utilized, i.e. 1000 jim, 1500 p.tm and 2000 .tm. Four sections of each thickness were utilized with four exposure sites per specimen (2 with 2 exposures, 2 with 4 exposures).All dentin sections were prepared from non-carious third molars using a hard tissue microtome. A thermistor was placed on the dentin surface opposite each lased site and temperature changes were recorded for approximately 50 sec. following lasing. Mean temperature elevations ranged from a high of 3.07 C for the 1000 xm section utilizing four exposures to a low of 0.37 0C for the 2000 m section utilizing two exposures. Analysis of Variance (p < .0001) and Duncan's Multiple Range Test (p =.05) indicated significant differences existed among the mean temperature elevations observed. While significant differences in temperature elevation can be observed both by numbers of exposures and by dentin thickness, it would appear that, under the conditions of this study, the temperature changes across CO2 lased dentin are all relatively low. It should be reiterated that the lasing parameters used in this study are far in excess of those necessary for preventive applications and are, in fact, in the range of exposures which will fuse enamel and dental porcelain, or remove dental caries. The modest temperature elevations observed, combined with the relatively severe exposure parameters utilized on thin sections of dentin, demonstrate the effective protective barrier which dentin provides for the dental pulp relative to heat damage from C02 lasing.
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