Streptococcus mutans, known to be an aetiologic agent of dental caries, also causes infective endocarditis (IE), although a comparison of isolates from the oral cavity and infected heart valve of the same patient has not been reported. In the present study, infected heart valve and dental plaque samples from a patient with IE were analysed. Broad-range PCR with DNA sequencing revealed that 50 clones from the dental plaque isolates were composed of oral streptococci and periodontopathic bacteria, whereas only Streptococcus mutans was detected in 50 clones from the heart valve. Eighteen strains of Streptococcus mutans were isolated from dental plaque and seven from the heart valve, and the biochemical properties of each were in accordance with those of Streptococcus mutans. DNA fingerprinting analysis revealed that all the oral isolates of Streptococcus mutans had similar patterns, which were different from those of the isolates from the infected heart valve. Western blotting using glucosyltransferase (GTF)-specific antiserum showed that the seven strains from the heart valve lacked the three types of intact GTF. In addition, the sucrose-dependent adhesion rates of these isolates were significantly lower than those of the oral isolates (P<0?001). Furthermore, the isolates from the heart valve were less susceptible to erythromycin and kanamycin. These results indicate that the properties of the Streptococcus mutans strains isolated from the infected valve were different from those of typical oral strains, which may be related to the effects of IE. INTRODUCTIONOral streptococci, which are major members of oral flora, frequently cause bacteraemia and infective endocarditis (IE) (Douglas et al., 1993). In 26 studies published between 1993 and 2003, 3784 cases of IE were presented, in which oral streptococci were considered to be involved in 21 %, second highest in frequency to Staphylococcus aureus (Moreillon & Que, 2004). According to a review of 848 IE cases in Japan, the most common type of micro-organism isolated from patient samples was Gram-positive streptococci (93?1 %), among which oral streptococci were frequently detected at a prevalence of 38?6 % (Nakatani et al., 2003). Streptococcus mutans, a major cause of dental caries, has occasionally been isolated from the blood of patients with IE and several case reports regarding the association of Streptococcus mutans and IE have been presented (Vose et al., 1987;Ullman et al., 1988;Gauduchon et al., 2001).The complete genome of Streptococcus mutans strain UA159 has been sequenced and was shown to be composed of approximately 2 million base pairs containing nearly 2000 open reading frames (Ajdić et al., 2002). Among them, three types of glucosyltransferase (GtfB, GtfC and GtfD) and protein antigen c (PAc) are known to be major cell surface proteins. In the case of IE, GtfB, GtfC and GtfD are known to induce the production of cytokines, such as interleukin-6 (IL-6) from monocytes (Shun et al., 2005). Several reports have discussed the association of PAc with IE, a...
Probiotic bacteria such as lactobacilli and bifidobacteria are considered to be non-pathogenic and non-toxigenic on the basis of long years of safe usage. However, some species of lactobacilli are thought to be associated with the development of dental caries. The purpose of the present study was to examine the cariogenicity of the probiotic bacterium Lactobacillus salivarius in rats. Rats were divided into six groups, and infected with L. salivarius LS1952R and/or Streptococcus mutans MT8148R. L. salivarius LS1952R became established in the oral cavity of rats and induced significant level of dental caries even when infected for only 5 days from 18 to 22 days of age. In addition, the caries scores of rats superinfected with both Streptococcus mutans MT8148R and L. salivarius LS1952R from 18 days of age were significantly higher than those infected with either L. salivarius LS1952R or S. mutans MT8148R alone. Since strain LS1952R can adhere to saliva-coated hydroxyapatites, it is concluded that L. salivarius strain LS1952R possesses an inherent cariogenic activity following adherence to the tooth surface.
Streptococcus mutans has been implicated as a primary causative agent of dental caries in humans. Bacterial components associated with the adhesion phase of S. mutans include cell-associated and cell-free glucosyltransferases (GTFs), as well as protein antigen c and proteins that bind glucan. At least four types of S. mutans glucan-binding protein (Gbp) have been identified; GbpA, GbpB, GbpC and GbpD. In the present study, GbpA-, GbpB- and GbpC-deficient mutants (AD1, BD1 and CD1, respectively) were constructed, and their cariogenic properties were evaluated by comparing them to those of their parent strain MT8148. All of the Gbp mutants showed lower levels of dextran binding, while the sucrose-dependent adhesion levels of AD1 and CD1 were lower than in the parental strain. The expression of each GTF was detected in the Gbp mutants, however, they had lower levels of cell-free-GTF activity than the parental strain. On the other hand, in acid tolerance assays, BD1 was the most sensitive among all of the tested strains. These results suggest that GbpA and GbpC in S. mutans have strong relationships with cariogenicity, while GbpB may have another biological function.
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