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Molecular and clinical analyses of the gene
encoding the collagen-binding adhesin of
Ryota Nomura,1Kazuhiko Nakano,1Naho Taniguchi,1
Jinthana Lapirattanakul,1Hirotoshi Nemoto,1Lisa Gro ¨nroos,2
Satu Alaluusua2,3and Takashi Ooshima1
1Department of Pediatric Dentistry, Osaka University Graduate School of Dentistry, Suita, Osaka,
2Department of Oral and Maxillofacial Diseases, Helsinki University Central Hospital, Helsinki,
3Department of Pediatric and Preventive Dentistry, Institute of Dentistry, University of Helsinki,
Received 25 October 2008
Accepted 3 December 2008
Streptococcus mutans is a known pathogen of dental caries and its major cell surface antigens
have been widely investigated. Recently, an approximately 120 kDa Cnm protein with binding
properties to type I collagen was identified, and its encoding gene (cnm) cloned and sequenced.
In the present study, we sequenced cnm from 47 different clinical S. mutans strains and found
that the nucleotide alignment of the collagen-binding domain was well conserved. We devised a
PCR method for identifying the cnm gene, examined the prevalence of cnm-positive S. mutans
strains in various mother–child groups, and assessed the significance of such strains for
transmission and dental caries. The detection rate of cnm-positive strains was significantly lower
in strains isolated from Japanese children in the 2000s (8.0%) as compared to those isolated in
the 1980s (15.8%) (P,0.05). Furthermore, the presence of S. mutans possessing cnm in
salivary specimens collected from 55 S. mutans-positive mother–child pairs was 40 and 32.7%
in the mothers and children, respectively. The frequency of cnm-positive children whose mothers
were also positive was 72%, which was significantly higher than that of cnm-positive children
with negative mothers (P,0.0001, odds ratio 17.5). In addition, clinical parameters indicating
dental caries were significantly increased in children with cnm-positive S. mutans in saliva
(n513), as compared to those with cnm-negative S. mutans (n515) and S. mutans-negative
children (n520) (P,0.01). These results indicate that cnm-positive S. mutans strains are closely
correlated with dental caries, while vertical transmission in cnm-positive mother–child pairs was
Streptococcus mutans, known to be a major pathogen of
dental caries, is classified into four serotypes (c, e, f and k)
based on the chemical composition of the serotype-specific
rhamnose glucose polymers (Hamada & Slade, 1980; Nakano
et al., 2004a). The distribution frequency of those serotypes
among clinical oral isolates has been investigated, which
showed that the majority, approximately 70–80%, were
than 5% of the strains classified as serotype f or k (Hirasawa
& Takada, 2003; Shibata et al., 2003; Nakano et al., 2004b).
The major cell surface protein antigens of S. mutans, which
include three types of glucosyltransferases (Aoki et al.,
1986; Pucci et al., 1987; Hanada & Kuramitsu, 1989), a
190 kDa protein antigen (PA) (Okahashi et al., 1989) and
four types of glucan-binding proteins (Gbps) (Banas et al.,
1997; Mattos-Graner et al., 2001; Sato et al., 1997; Shah &
Russell, 2004), have been widely investigated in studies
related to its virulence for dental caries. Recently, the
120 kDa Cnm protein encoding the collagen-binding
adhesin of S. mutans was characterized, and its encoding
gene was cloned and sequenced (Sato et al., 2004). The
distribution frequency of the cnm gene in 102 S. mutans
strains in our previous study was shown to be 21.4%, with
cnm-positive strains showing a predominant distribution
among strains with the minor serotypes f and k, which
The GenBank/EMBL/DDBJ accession numbers for the cnm sequences
of the 47 clinical isolates reported in this paper are AB465259–
Journal of Medical Microbiology (2009), 58, 469–475
007559G2009 SGMPrinted in Great Britain 469
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