Most common infection in patients with prosthetic valves is –
**Core Concept**
In patients with prosthetic valves, the risk of infection is increased due to the presence of a foreign object in the body. This can lead to bacterial colonization and subsequent endocarditis, an infection of the heart valves. The most common pathogen responsible for this infection is a bacterium that can form a biofilm on the prosthetic valve.
**Why the Correct Answer is Right**
Staphylococcus epidermidis is a coagulase-negative staphylococcus that is commonly found on the skin and mucous membranes. It has a propensity to form a biofilm on prosthetic devices, including heart valves, which protects it from antibiotics and host immune response. This biofilm formation is a key factor in the pathogenesis of prosthetic valve endocarditis. The biofilm matrix is composed of polysaccharides and proteins that provide a scaffold for bacterial colonization and growth.
**Why Each Wrong Option is Incorrect**
**Option A:** Streptococcus viridans is a common cause of endocarditis in patients with pre-existing heart disease, but it is not the most common cause in patients with prosthetic valves.
**Option B:** Staphylococcus aureus is a common cause of endocarditis, but it is more commonly associated with skin and soft tissue infections.
**Option C:** Escherichia coli is a common cause of urinary tract infections, but it is not typically associated with prosthetic valve endocarditis.
**Clinical Pearl / High-Yield Fact**
In patients with prosthetic valves, the risk of endocarditis is highest in the first year after valve replacement, and the most common pathogens are Staphylococcus epidermidis and Staphylococcus aureus.
**Correct Answer:** C. Staphylococcus epidermidis