Multilocus sequence typing analysis of Streptococcus mutans strains with the cnm gene encoding collagen-binding adhesin.

Streptococcus mutans is one of the oral pathogens associated with infective endocarditis (IE). With respect to bacterial binding ability to the extracellular matrix, the Cnm protein, a cell surface collagen-binding adhesin of S. mutans, is known as one of the possible virulence factors with regard to IE. In this study, we aimed to determine the distribution of the cnm gene, which encodes Cnm, in a large number of clinical isolates of S. mutans from Thai subjects. Then, the cnm-positive strains were classified using a multilocus sequence typing (MLST) scheme, which we constructed previously. In addition, the data were analysed together with our previous MLST data of cnm-positive strains from Japan and Finland in order to evaluate the clonal relationship among S. mutans strains harbouring the cnm gene. The cnm gene was detected in 12.4 % of all 750 Thai isolates, and serotype f showed the highest rate of detection (54.5 %). According to the MLST data, two clonal complex groups were revealed as the important clones related to cnm-positive S. mutans from various origins of isolation. Moreover, the collagen-binding properties of S. mutans strains with the cnm gene were significantly greater than those of strains without the gene, although four cnm-negative strains classified into two sequence types (STs), ST110 and ST136, showed extremely high collagen-binding rates suggesting the presence of additional genes involved with collagen binding in these STs. Taken together, these results provided information on both epidemiological as well as evolutional aspects of S. mutans possessing the cnm gene.