Which organism is the most common etiologic agent of infections associated with the surgical insertion of prosthetic devices such as artificial heart valves and cerebrospinal fluid shunts?

• A. Corynebacterium urealyticum
• B. Staphylococcus capitis
• C. Staphylococcus epidermidis
• D. Streptococcus mutans

Answer: (C)

Prosthetic-device infections are dominated by organisms that live on the skin and can cling to artificial surfaces, forming biofilms that protect the bacteria from antibiotics and immune defenses. Staphylococcus epidermidis does this particularly well, sticking to plastics and other materials used in artificial heart valves and cerebrospinal fluid shunts and producing a biofilm that enables persistent infection. This combination of skin origin, strong adherence to foreign surfaces, and robust biofilm formation makes it the most common cause of infections associated with implanted devices. Other organisms listed are less typically associated with prosthetic infections: oral Streptococcus mutans is linked to dental caries, Corynebacterium urealyticum is more often linked to urinary tract or catheter-associated issues in specific contexts, and Staphylococcus capitis, while a skin bacterium, is less commonly the leading cause of these device-related infections than epidermidis.