The most common etiologic agent of infections associated with prosthetic devices such as artificial heart valves and CSF shunts is which organism?

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

Answer: (C)

In device-associated infections, organisms that live on skin and can cling to artificial surfaces and persist there are the usual culprits. Staphylococcus epidermidis fits this scenario best. It’s a coagulase-negative staphylococcus commonly found on the skin and mucous membranes. When a prosthetic device such as an artificial heart valve or a CSF shunt is in place, S. epidermidis readily adheres to the surface and forms a biofilm—a protective, slime-covered community of bacteria. This biofilm shields the bacteria from antibiotics and the immune system, allowing a low-grade, chronic infection around the device. Because of these traits, S. epidermidis is the leading cause of prosthetic device infections. The other organisms listed are less typically involved in this setting: Streptococcus mutans is mainly linked to dental caries, Corynebacterium urealyticum to urinary tract infections, and Staphylococcus capitis, while a skin inhabitant, is not the principal cause of prosthetic device infections.