Staphylococcus epidermidis is a common type of bacteria that is a ubiquitous resident of the human body. This organism is classified as a Gram-positive coccus, meaning it is spherical and retains the crystal violet stain. It is an integral part of the normal human microbiota, primarily colonizing the skin and mucous membranes. While generally harmless in its usual habitat, S. epidermidis is a major concern within clinical environments, particularly in patients with weakened immune systems.
The Dual Nature of S. epidermidis
This organism maintains a delicate balance with its host, existing in a relationship known as commensalism. As a permanent resident of the skin, S. epidermidis actively contributes to a healthy skin barrier and helps maintain homeostasis. It occupies available space and consumes nutrients, which effectively prevents more aggressive pathogens, such as the related Staphylococcus aureus, from colonizing the skin surface.
The bacterium’s role shifts when the natural physical barrier of the skin or mucosa is compromised. S. epidermidis is an opportunistic pathogen, causing disease only when it gains access to deeper tissues or the bloodstream. This transition occurs in immunocompromised individuals or when a medical procedure breaches the body’s defenses. The organism lacks the aggressive toxins and enzymes produced by more virulent staphylococci, relying instead on exploiting a weakened host.
Biofilms and Medical Device Infections
The most significant mechanism by which S. epidermidis causes infection is its ability to form a biofilm. A biofilm is a complex community of bacterial cells encased within a self-produced, protective matrix. This matrix is composed of extracellular polymeric substances (EPS), primarily consisting of polysaccharides and proteins.
The formation of this adhesive layer allows the bacteria to stick firmly to non-biological surfaces, making S. epidermidis the most common cause of infections associated with implanted medical devices. Examples of frequently colonized devices include central venous catheters, prosthetic joints, heart valves, and shunts. The initial adhesion to these foreign materials, often plastic or metal, is a consequence of the organism’s natural tendency to stick.
Once established, the biofilm protects the embedded bacteria from the host’s immune response cells and antibodies. This matrix also significantly impedes the penetration of antibiotic drugs. The presence of a biofilm transforms this typically benign skin resident into a persistent and difficult-to-treat threat in a healthcare setting.
Addressing Infections and Antibiotic Resistance
Treating infections caused by S. epidermidis presents substantial clinical challenges due to biofilm formation and widespread antibiotic resistance. Many strains have acquired genetic material making them resistant to methicillin and related penicillin-class antibiotics. This results in Methicillin-Resistant S. epidermidis (MRSE), which limits therapeutic options.
Because of the high prevalence of resistance, the glycopeptide antibiotic vancomycin is the primary treatment for serious S. epidermidis infections. Vancomycin is administered intravenously, but its effectiveness is diminished when the bacteria have formed a mature biofilm. The protective EPS layer prevents sufficient antibiotic concentrations from reaching the bacteria deep within the matrix.
The established protocol for resolving a device-associated infection requires the removal and replacement of the contaminated medical implant. Although antibiotics are administered to clear free-floating bacteria, surgical removal of the colonized device is necessary to eliminate the shielded bacterial community within the biofilm. This highlights the difficulty in eradicating the infection with drug therapy alone.