Native Valve Endocarditis

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I was doing usmleword, and it said Staph. epidermidis is an uncommon cause of native vale endocarditis. What exactly does Native valve mean? Does that mean the valve has already been affected or does that mean its a new valve that's never been affected.

Thanks!

 

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Native valve is what the patient is born with as compared to a prosthetic valve.
It is the regurgitant lesion which predisposes to native valve endocarditis and the most common organism(s) are the viridans group since there is transient bacteremia every time someone chews/brushes their teeth. Normally this does not cause any problems but with a regurgitant valve lesion (due to shearing forces) providing a fertile ground for these organisms they cause endocarditis. In fact anything which causes transient bacteremia (e.g. a cystoscopy) can cause native valve endocarditis (E.Coli in this case).
Prosthetic valve endocarditis is most commonly caused by Staph. epidermidis which is a normal commensel but loves foreign material.
Hope this helps.

Viridans streptococci have the unique ability to synthesize dextrans from glucose, which allows them to adhere to fibrin-platelet aggregates at damaged heart valves. This mechanism underlies their ability to cause subacute valvular heart disease following their introduction into the bloodstream (e.g., following dental extraction).
The organisms are most abundant in the mouth, and one member of the group, S. mutans, is the etiologic agent of dental caries in most cases and populations. Others may be involved in other mouth or gingival infections.