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.
Antibodies are much smaller than bacteria in physical size.
The antibodies can attach to the bacterial antigenic sites in even the most turbulent areas of the heart and by any of several different methods of action, cause their destruction. Less virulent bacteria do not elicit strong production of antibodies and are able to live in relative safety on heart valve surfaces. When bacteria are detected in a sample of blood, physicians have the responsibility of deciding whether those bacteria may represent an acute threat, as for example a Salmonella bacteremia, a chronic threat, as for example a bacterial infective endocarditis caused by a less virulent Streptococcus sp., or merely a contaminant such as Propionibacterium acnes . This is one reason why a sequence of several samples has to be taken and examined. If enterococci are found in several serial samples, the finding is significant and there may be a high level of resistance to antimicrobial therapy.