There are only very few virulence factors known for the major players, E. faecalis and E. faecium. In general, the bacteria are very resistant to harsh environments and they inhabit many different ecological niches, including humans. Endocarditis , endo- inside. Chronically over time localized inflammatory reaction causes the heart valves to become hardened or stenotic and they may not be able to function effectively. Due to the fluid dynamics involved in blood flow through the heart, white blood cells cannot adhere to the heart valve surfaces because of their large size.
Fluid turbulence has much less of an effect on bacteria which are much smaller in physical size.
The bacteria are able to adhere to the valve surfaces which in effect are a safe haven from white blood cells which would phagocytize the bacteria in slower moving, less turbulent areas of the blood circulatory system. As bacteria multiply they are sloughed off from foci within the heart causing a constant or recurring low level bacteremia. Bacteria which fail to maintain adherence are returned to the slower moving areas where they are eaten by white blood cells, particularly neutrophils and to some extent monocytes. Paradoxically, when bacteria cause endocarditis, it is a general indication of a lack of virulence factors for the type of organism involved. This is because the more virulent bacteria have antigenic determinant sites which induce a strong production of antibodies from lymphocytes.