Staphylococcus epidermidis is a type of bacteria that is spherical in shape and typically arranges itself in grape-like clusters. It is classified as a Gram-positive bacterium, which means it retains a purple stain when subjected to a specific laboratory test. This bacterium can grow both with and without oxygen, indicating it is a facultative anaerobe. Found widely in various environments, S. epidermidis is one of more than 40 species within the genus Staphylococcus.
A Common Resident
Staphylococcus epidermidis is a widespread bacterium commonly found on the skin and mucous membranes of humans. It is part of the normal human microbiota. This bacterium is generally harmless in its usual habitat and can even offer benefits to its human host.
Within the skin’s microbial community, S. epidermidis actively contributes to maintaining skin health and balance. It can compete with more harmful bacteria, preventing them from colonizing and causing disease. This competition involves producing antimicrobial peptides and stimulating the host’s immune response.
When It Becomes a Problem
While typically a benign resident, Staphylococcus epidermidis can transform into an opportunistic pathogen under specific circumstances. This often occurs when the body’s natural defenses are weakened, such as in individuals with compromised immune systems. Breaches in the skin barrier, like those from surgical incisions or wounds, also provide an entry point for the bacteria into deeper tissues.
The presence of medical devices, including catheters, prosthetic joints, and pacemakers, represents a significant risk factor for S. epidermidis infections. During implantation, bacteria from the skin can inadvertently transfer to the device surface. Once attached, S. epidermidis can form biofilms, which are communities of bacteria encased in a protective matrix. This biofilm acts as a shield, protecting the bacteria from the host’s immune system and making antibiotic treatment challenging.
Types of Infections It Causes
When Staphylococcus epidermidis transitions from a harmless resident to a pathogen, it primarily causes healthcare-associated infections. A common example is catheter-related bloodstream infections, where the bacteria migrate from the skin surface along the catheter into the bloodstream.
Staphylococcus epidermidis is also a frequent cause of prosthetic joint infections, leading to symptoms like pain and pus around the implant site. It also contributes to infective endocarditis, particularly in patients with prosthetic heart valves. Other infections include those related to cardiac devices and central nervous system shunts, which can manifest as localized inflammation or systemic signs like fever and sepsis.
Diagnosis and Treatment
Diagnosing Staphylococcus epidermidis infections often involves culturing samples from suspected infected sites, such as blood or tissue. Distinguishing a true infection from mere contamination can be difficult, as S. epidermidis is so common on the skin. Repeated isolation from multiple blood cultures taken at different times indicates an infection.
Treating S. epidermidis infections presents challenges due to the bacterium’s tendency for antibiotic resistance and biofilm formation. Many strains, especially those encountered in healthcare settings, are resistant to methicillin, a common antibiotic. This widespread resistance often makes vancomycin the preferred initial antibiotic choice for serious S. epidermidis infections.
However, vancomycin’s effectiveness against biofilms can be limited. Often, successful treatment of device-related infections necessitates the removal of the infected medical device in addition to antibiotic therapy. Combinations of antibiotics, such as vancomycin or daptomycin with rifampin, have shown improved activity against S. epidermidis biofilms.