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Virulence. 2017 Jan 2;8(1):18-29. doi: 10.1080/21505594.2016.1195538. Epub 2016 Jun 3.

Heterologous expression of Streptococcus mutans Cnm in Lactococcus lactis promotes intracellular invasion, adhesion to human cardiac tissues and virulence.

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a Department of Physiological Sciences , Piracicaba Dental School, University of Campinas , Piracicaba , SP , Brazil.
b Center for Oral Biology, University of Rochester Medical Center , Rochester , NY , USA.
c Department of Oral Biology , University of Florida College of Dentistry , Gainesville , FL , USA.
d Philips Institute for Oral Health Research, Virginia Commonwealth University , Richmond , VA , USA.
e Department of Medicine/Hematology-Oncology Division and Department of Pathology and Laboratory Medicine , University of Rochester Medical Center , Rochester , NY , USA.
f Department of Surgery , Cardiac Division, University of Rochester School of Medicine and Dentistry , Rochester , NY , USA.


In S. mutans, the expression of the surface glycoprotein Cnm mediates binding to extracellular matrix proteins, endothelial cell invasion and virulence in the Galleria mellonella invertebrate model. To further characterize Cnm as a virulence factor, the cnm gene from S. mutans strain OMZ175 was expressed in the non-pathogenic Lactococcus lactis NZ9800 using a nisin-inducible system. Despite the absence of the machinery necessary for Cnm glycosylation, Western blot and immunofluorescence microscopy analyses demonstrated that Cnm was effectively expressed and translocated to the cell wall of L. lactis. Similar to S. mutans, expression of Cnm in L. lactis enabled robust binding to collagen and laminin, invasion of human coronary artery endothelial cells and increased virulence in G. mellonella. Using an ex vivo human heart tissue colonization model, we showed that Cnm-positive strains of either S. mutans or L. lactis outcompete their Cnm-negative counterparts for tissue colonization. Finally, Cnm expression facilitated L. lactis adhesion and colonization in a rabbit model of infective endocarditis. Collectively, our results provide unequivocal evidence that binding to extracellular matrices mediated by Cnm is an important virulence attribute of S. mutans and confirm the usefulness of the L. lactis heterologous system for further characterization of bacterial virulence factors.


Lactococcus lactis; Streptococcus mutans; bacterial pathogenesis; collagen-binding protein; infective endocarditis

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