Professional and Linguistic Assessments Board (PLAB) Practice Exam

What is the most common organism found in central lines?

1. Staphylococcus Aureus

2. Staphylococcus Epidermidis

3. Escherichia Coli

4. Enterococcus Faecalis

The correct answer is: Staphylococcus Epidermidis

Staphylococcus epidermidis is recognized as the most common organism associated with infections related to central lines. This coagulase-negative Staphylococcus is part of the normal skin flora and typically does not cause disease in healthy individuals. However, when it enters the bloodstream through a central line, particularly in immunocompromised patients or those with foreign body implants, it can lead to opportunistic infections. Central venous catheters, often used for prolonged intravenous access, provide a pathway for these bacteria to enter the bloodstream, leading to infections known as catheter-associated bloodstream infections (CABSI). Staphylococcus epidermidis is known for its ability to form biofilms on medical devices, which can make infections difficult to treat. Other organisms listed, such as Staphylococcus aureus, Escherichia coli, and Enterococcus faecalis, are also capable of causing infections but are less frequently isolated in the context of central line-associated infections compared to Staphylococcus epidermidis. Staphylococcus aureus is more associated with acute infections and is often more virulent, while E. coli and Enterococcus faecalis are primarily found in different clinical contexts, such as urinary tract infections or entero-related infections.