Cnm is a major virulence factor of invasive S treptococcus mutans and part of a conserved three‐gene locus

Summary Cnm, a collagen‐ and laminin‐binding protein present in a subset of S treptococcus mutans strains, mediates binding to extracellular matrices ( ECM ), intracellular invasion and virulence in the G alleria mellonella model. Antibodies raised against C nm were used to confirm expression and the cell surface localization of C nm in the highly invasive OMZ 175 strain. Sequence analysis identified two additional genes ( cna B and cbp A ) encoding putative surface proteins immediately upstream of cnm . Inactivation of cna B and cbp A in OMZ 175, individually or in combination, did not decrease the ability of this highly invasive and virulent strain to bind to different ECM proteins, invade human coronary artery endothelial cells ( HCAEC ), or kill G. mellonella . Similarly, expression of cna B and cbp A in the cnm − strain UA 159 revealed that these genes did not enhance C nm‐related phenotypes. However, integration of cnm in the chromosome of UA 159 significantly increased its ability to bind to collagen and laminin, invade HCAEC , and kill G. mellonella . Moreover, the presence of antibodies against Cnm nearly abolished the ability of OMZ 175 to bind to collagen and laminin and invade HCAEC , and significantly protected G. mellonella against OMZ 175 infection. We concluded that neither C na B nor C bp A is necessary for the expression of C nm‐related traits. We also provided definitive evidence that C nm is an important virulence factor and a suitable target for the development of novel preventive and therapeutic strategies to combat invasive S . mutans strains.