Molecular characterization of Streptococcus mutans strains containing the cnm gene encoding a collagen-binding adhesin.
OBJECTIVE
Streptococcus mutans, known to be a major pathogen of dental caries, is also considered to cause infective endocarditis. Its 120-kDa Cnm protein binds to type I collagen, which may be a potential virulence factor. In this study, we characterized S. mutans clinical strains focusing on the cnm gene encoding Cnm.


METHODS
A total of 528 S. mutans strains isolated from Japanese, Finnish, and Thai subjects were investigated. Using molecular techniques, the distribution frequency of cnm-positive strains and location of the inserted cnm were analyzed. Furthermore, isogenic mutant strains were constructed by inactivation of the cnm gene, then their biological properties of collagen-binding and glucan-binding were evaluated. Southern hybridization of the genes encoding glucan-binding proteins was also performed.


RESULTS
The distribution frequency of cnm-positive strains from Thai subjects was 12%, similar to that previously reported for Japanese and Finnish subjects. Furthermore, the location of insertion of cnm was the same in all cnm-positive clinical isolates. As for the cnm-inactivated mutant strains constructed from 28 clinical isolates, their collagen-binding activity was negligible. In addition, glucan-binding activity in the cnm-positive clinical isolates was significantly reduced and corresponded to a lack of gbpA encoding glucan-binding protein A.


CONCLUSIONS
Our results indicate that strains with cnm genes, the most crucial factor for the collagen-binding property of S. mutans, are detectable at similar frequencies over several different geographic locations. In addition, the common properties of these strains are a high level of collagen-binding activity and tendency for a low level of glucan-binding activity.
Nakano
K
K
Department of Pediatric Dentistry, Osaka University Graduate School of Dentistry, Suita, Osaka, Japan.
Nomura
R
R
Taniguchi
N
N
Lapirattanakul
J
J
Kojima
A
A
Naka
S
S
Senawongse
P
P
Srisatjaluk
R
R
Grönroos
L
L
Alaluusua
S
S
Matsumoto
M
M
Ooshima
T
T
D018829:Adhesins, Bacterial / Q000235:genetics*; D015139:Blotting, Southern; D002352:Carrier Proteins / Q000235:genetics*; D003094:Collagen / Q000378:metabolism*; D003731:Dental Caries / Q000382:microbiology; D005387:Finland; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D005936:Glucans / Q000378:metabolism; D006801:Humans; D007564:Japan; D016133:Polymerase Chain Reaction; D011485:Protein Binding / Q000235:genetics; D012463:Saliva / Q000382:microbiology; D013295:Streptococcus mutans / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity; D013785:Thailand
D018829:Adhesins, Bacterial; D002352:Carrier Proteins; C488758:Cnm protein, Streptococcus mutans; D005936:Glucans; D003094:Collagen