Streptococcus mutans and Streptococcus sobrinus are major pathogens causing dental caries in humans. A simple and rapid method to detect these species in human saliva simultaneously was developed using the polymerase chain reaction (PCR). Chromosomal DNA was extracted by boiling bacterial cells in lysis solution containing 1% Triton X-100. Oligonucleotide primers specific for portions of the glucosyltransferase genes (gtfB of S. mutans and gtfI of S. sobrinus) were designed. After PCR using two sets of these primers, S. mutans and S. sobrinus were specifically identified. The method was capable of amplifying DNA fragments specific for these species from chromosomal DNA extracted from 1 x 10(3) cells, or from 10 microliters of clinical saliva samples containing 1 x 10(3) colony-forming units of either streptococcal species. A second PCR, using the first PCR product as a template with newly designed internal primers, made it possible to detect 1 x 10(2) colony-forming units of either streptococcal species in 10 microliters of saliva samples. These results indicate that the PCR method developed in this study is useful for detecting S. mutans and S. sobrinus in saliva and that it can be used in epidemiological studies to evaluate the prevalence level of these organisms.

A possible mechanism of acquired acid resistance of lased enamel was proposed on the basis of the investigations of optical properties, compositional and structural changes and permeability of lased and unlased human dental enamel. Lased enamel showed a high positive birefringence, suggesting the formation of ‘microspaces’ in enamel. No new products were found, though a decrease of lattice strain and a slight a-axis contraction were recognized in lased enamel compared with unlased enamel. The contents of water, carbonate and organic substances were reduced in lased enamel. Gradual changes of birefringence were observed in lased enamel during treatment with acid solutions, and this change was attributed to mineralization of the microspaces. The ions released by an acid decalcification would be trapped in the microspaces in lased enamel, whereas such ions diffuse to the surrounding solution in unlased enamel.

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Methyl mercaptan production by oral bacteria is thought to be one of the main causes of oral malodor. We examined the ability of periodontopathic Porphyromonas gingivalis to produce methyl mercaptan from L-methionine and found that the invasive strains W83 and W50 produced large amounts of methyl mercaptan. We cloned and sequenced the mgl gene encoding L-methionine-␣-deamino-␥-mercaptomethane-lyase (METase) from P. gingivalis W83. The structural mgl gene consisted of 1,200 bp and encoded a 43.3-kDa protein. To examine the role of methyl mercaptan in the pathogenesis of P. gingivalis, a METase-deficient mutant of P. gingivalis W83 was constructed. The methionine degradation activity and virulence of the mutant (M1217) and the parent strain (W83) in mice were compared. M1217 showed a marked decrease in the formation of methyl mercaptan from L-methionine and decreased virulence compared with the wild-type strain W83. These results suggest that methyl mercaptan not only is one of the sources of oral malodor, but may also play a role in the pathogenicity of P. gingivalis.Oral malodor is caused mainly by volatile sulfur compounds (VSCs), such as hydrogen sulfide, methyl mercaptan, and dimethyl sulfide (21). Of these VSCs, hydrogen sulfide and methyl mercaptan are predominant in mouth air. Both compounds are highly toxic, especially methyl mercaptan (21). VSCs can increase the permeability of the oral mucosa (16) and decrease protein or collagen synthesis (6,8). It is possible that the presence of methyl mercaptan within a periodontal pocket is involved in the induction or progression of periodontal disease. Coil et al. (2) reported that the increase in the ratio of methyl mercaptan to hydrogen sulfide in human gingival crevicular sites is correlated with deeper pockets or bleeding pockets. Exposure to methyl mercaptan alters protein synthesis in human gingival fibroblasts (7) and inhibits cell migration in periodontal ligament cells (11). These findings suggest that methyl mercaptan not only may be responsible for oral malodor but also may contribute to the pathogenesis of periodontal disease.Methyl mercaptan is produced from L-methionine by the enzymatic action of L-methionine-␣-deamino-␥-mercaptomethane-lyase (METase), which catalyzes the ␣,␥ elimination of L-methionine to produce ␣-ketobutyrate, methyl mercaptan, and ammonia. This enzyme is detected in anaerobic, nonoral microorganisms, such as Pseudomonas, Trichomonas, and Clostridium (4, 5, 9, 13). In addition, Porphyromonas gingivalis, a black-pigmented anaerobe, which is implicated as a major pathogen in adult periodontitis, is known to produce large amounts of methyl mercaptan in human serum (18). However, little is known about P. gingivalis METase and the role of methyl mercaptan in the pathogenesis of this organism. In this study, we cloned the mgl gene homolog encoding METase from the virulent strain P. gingivalis W83 and confirmed its nucleotide sequence. To determine the role of METase in the pathogenicity of P. gingivalis, we constructed a METase-defici...