Our bodies are home to microscopic organisms, many living harmlessly on our skin and inside us. These communities are known as the human microbiome. Staphylococcus epidermidis is a common bacterium found on nearly everyone’s skin and mucous membranes. While usually benign, it can sometimes cause health problems under specific conditions.
The Nature of Staphylococcus epidermidis
Staphylococcus epidermidis is a Gram-positive bacterium, retaining a purple stain in a laboratory test due to its cell wall composition. These spherical bacteria often arrange in grape-like clusters. It is also coagulase-negative, distinguishing it from other staphylococci like Staphylococcus aureus. The absence of the coagulase enzyme, which clots plasma, identifies it in laboratory settings.
It is a widespread part of the normal human microbiota, found predominantly on the skin, particularly in areas like the armpits, head, and inside the nostrils. It can be observed on the skin of most healthy newborns within hours of birth. It generally exists as a harmless commensal organism, living on or in a host without causing disease.
When Staphylococcus epidermidis Becomes a Problem
While typically harmless, Staphylococcus epidermidis can become an opportunistic pathogen, causing infections when body defenses are weakened or it gains access to internal sterile sites. This often occurs in individuals with compromised immune systems or indwelling medical devices. Patients in hospitals, those undergoing surgery, or individuals with damaged skin barriers are at increased risk.
A factor in its ability to cause disease is its capacity to form biofilms. Biofilms are protective layers of bacteria that adhere to surfaces, especially medical devices like catheters, prosthetic joints, and shunts. Within these biofilms, bacteria are shielded from antibiotics and the immune response, making infections difficult to eradicate. Adherence to foreign materials is often the initial step in these infections.
Common Infections Associated with Staphylococcus epidermidis
Staphylococcus epidermidis contributes to healthcare-associated infections, particularly those linked to implanted medical devices. Catheter-related bloodstream infections (CRBSIs) are a common example, where bacteria migrate from the skin along the catheter surface into the bloodstream. This can lead to systemic symptoms like fever and low blood pressure.
The bacterium is also implicated in infections of prosthetic joints, causing pain and inflammation around the implant site. It is also a cause of prosthetic valve endocarditis, an infection of artificial heart valves, where it can form vegetations on the valves. Other implanted devices, such as shunts and pacemakers, are also susceptible to infection due to its ability to colonize these foreign materials and form protective biofilms.
Addressing Staphylococcus epidermidis Infections
Managing Staphylococcus epidermidis infections presents challenges, primarily due to antibiotic resistance and the protective nature of biofilms. Many strains, particularly in healthcare settings, have developed resistance to common antibiotics, including methicillin. Methicillin resistance means initial empirical treatment often involves antibiotics like vancomycin, with specific choices guided by susceptibility testing.
Eradicating biofilm-protected bacteria is difficult because the biofilm matrix impedes antibiotic penetration and immune cell access. Therefore, in many cases involving infected medical devices, successful treatment necessitates removal or exchange of the contaminated device in addition to antibiotic therapy. Prevention strategies, such as rigorous sterilization of medical instruments and strict aseptic techniques during procedures, are important in reducing the incidence of these infections.