Streptococcus mutans (Sm) has long been recognized as a major pathogen of dental caries, the most common infectious disease in humans. What is much less appreciated is its role in extra-oral infections. Sm is an opportunistic pathogen frequently identified in human bacteremias and is an etiologic agent of infectious endocarditis (IE). IE, a valvular vegetation of the endothelial layer, is a serious cardiovascular disease with often fatal outcomes directly related to dental procedures. There is now strong evidence that Sm is involved in hemorrhagic stroke, which occurs when a blood vessel ruptures in the brain. Additionally, epidemiological and DNA sequencing evidence supports a contributing role of Sm to atherosclerosis. Atherosclerosis is a complex inflammatory disease afflicting medium and large sized arteries and is the leading cause of death in the USA. The commonality of these diseases is that they are diseases of the cardiovascular system. The ability of a pathogen to attach to and invade endothelial tissues has previously been shown to be required for virulence in IE and the ability to invade endothelial cells has been shown to correlate with endocardititis severity. We have previously reported that specific strains of Sm can invade human cardiovascular aortic endothelial cells (HCAEC). New data demonstrate that the HCAEC invasion phenotype correlates with the presence of a gene encoding a collagen binding protein, Cnm, and that deletion of cnm renders the strains unable to invade. Sm OMZ175, a strain that expresses Cnm, produces significant pathology compared to control mice in a mouse model of accelerated atherosclerosis. Intracellular pathogens have evolved multiple pathways and mechanisms to enter, traffic and survive within eukaryotic cells. Thus, the mode of entry plays a major role in determining bacterial fate. There are no reports about the cellular events that govern Sm entry into cells. Our overall hypothesis is that strains of Sm expressing Cnm, such as our model organism OMZ175, are able to adhere to, enter, and persist in HCAECs and that the mechanism of entry is critical to the trafficking and survival of Sm intracellularly. Our workig hypothesis to be tested in this proposed project is that invasive Sm enters endothelial cells using specific mechanisms and that Cnm plays a central role in this entry. Understanding the mechanisms that specific strains of a ubiquitous oral pathogen have acquired that expand its virulence to sites outside of the oral cavity would provide further insight into the molecular details of adhesin mediated streptococci interactions with its host.
The specific aims of this application are 1) Determine the mechanism of entry of Sm into HCAEC and 2) Determine the contribution of Cnm in the entry process. Our own data and that of others indicate that invasive strains of Sm also invade oral cells and can be detected in predentate children. In addition, cnm has now been found in strains of S. sanguinis, S. suis and S. rattus. Therefore these studies will have significance beyond CVD pathology. In addition, this project would contribute information concerning the application of cnm as a biomarker for hypervirulent strains of Sm.
This project is designed to determine the mechanisms that certain strains of Streptococcus mutans (Sm), the bacteria that causes tooth decay and infectious endocarditis, use to invade human cardiovascular endothelial cells. Understanding the mechanisms that specific strains of Sm have acquired that expand its virulence to sites outside of the oral cavity would provide insight into the details of oral streptococci interactions with its host.