**Core Concept**
Prosthetic valve endocarditis (PVE) is a type of infective endocarditis that occurs in patients with prosthetic heart valves. The risk of developing PVE is higher in the first year after valve replacement, but it can occur at any time. The microbiology of PVE differs from that of native valve endocarditis, with a higher incidence of coagulase-negative staphylococci, particularly Staphylococcus epidermidis.

**Why the Correct Answer is Right**
Staphylococcus epidermidis is a common skin commensal bacterium that can colonize prosthetic materials, including heart valves. It produces biofilms that adhere to the valve surface, making it difficult to eradicate with antibiotics. S. epidermidis has a low virulence compared to other pathogens but can cause significant morbidity and mortality in patients with PVE. The biofilm formation and adherence to prosthetic materials are key factors in the pathogenesis of S. epidermidis-induced PVE.

**Why Each Wrong Option is Incorrect**
**Option A:** Staphylococcus aureus is a common cause of native valve endocarditis but is less commonly associated with PVE, especially in the later stages.

**Option B:** Streptococcus viridans is a common cause of subacute bacterial endocarditis but is not typically associated with PVE.

**Option D:** HACEK (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella) organisms are rare causes of endocarditis and are not typically associated with PVE.

**Clinical Pearl / High-Yield Fact**
In patients with PVE, a high index of suspicion is necessary for early diagnosis, as the clinical presentation may be subtle. A prolonged course of antibiotics, often with the addition of anticoagulation, is typically required to treat S. epidermidis-induced PVE.

**✓ Correct Answer: C. Staph. epidermidis**