What is the frequency of Staphylococcus epidermidis (S. epidermidis) as a true pathogen?

From the Guidelines

Staphylococcus epidermidis is a true pathogen in approximately 30-40% of cases where it's isolated from clinical specimens, particularly in individuals with compromised immune systems or those with indwelling medical devices. This bacterium is commonly associated with infections of prosthetic joints, heart valves, vascular catheters, cerebrospinal fluid shunts, and other implanted medical devices, where it forms biofilms that allow it to adhere to device surfaces and resist both immune responses and antibiotics 1. The management of S. epidermidis infections often involves the use of vancomycin for methicillin-resistant strains or nafcillin/oxacillin for susceptible strains, often combined with rifampin for biofilm penetration, and in many cases, complete eradication requires removal of the infected device 1. Some studies have demonstrated that antibiotic concentrations must be 100–1000 times greater to kill sessile (biofilm) bacteria than to kill planktonic (in solution) bacteria, and the use of antibiotic lock therapy has been shown to be effective in sterilizing catheters and salvaging them in some cases 1. However, the effectiveness of antibiotic lock therapy can vary depending on the pathogen and the specific situation, and most clinicians would not feel comfortable providing antibiotic lock therapy without a full course of parenteral therapy in certain cases, such as bloodstream infection in a patient with neutropenia or moderately severe infection with any pathogen-host combination 1. In the context of prosthetic valve endocarditis, S. epidermidis is the predominant offending organism in early-onset cases, usually defined as endocarditis during the first 2 months after surgery 2. Overall, the pathogenicity of S. epidermidis stems from its ability to produce extracellular polysaccharides forming protective biofilms, rather than the production of aggressive toxins seen in more virulent staphylococcal species like S. aureus. Key considerations in the management of S. epidermidis infections include:

• The use of appropriate antibiotic therapy, such as vancomycin or nafcillin/oxacillin, often combined with rifampin for biofilm penetration
• The potential need for removal of the infected device in order to achieve complete eradication
• The use of antibiotic lock therapy in certain cases, such as intraluminal infection
• The importance of selecting patients for antibiotic lock therapy based on a high likelihood of intraluminal infection.

From the Research

Frequency of Staphylococci Epidermidis as a True Pathogen

• Staphylococcus epidermidis is a common cause of native valve endocarditis, particularly in cases acquired in a nosocomial setting 3.
• It is also a frequent cause of device-associated infections, such as those involving biofilm-producing methicillin-resistant S. epidermidis (MRSE) strains 4.
• The ability of S. epidermidis to cause disease is linked to its natural niche on human skin and its ability to attach and form biofilm on foreign bodies 5.
• S. epidermidis is the most common cause of primary bacteremia and infections of indwelling medical devices 5.

Clinical Characteristics of Infections

• Infections caused by S. epidermidis can be associated with hemodialysis, the presence of a long-term indwelling central catheter or pacemaker, or a recent invasive procedure 3.
• Nosocomial cases of S. epidermidis infections may have a higher rate of methicillin resistance, making treatment with vancomycin more likely 3.
• However, treatment with vancomycin may not always be effective, and alternative therapies such as daptomycin may be necessary 3, 4.

Diagnosis and Treatment

• Distinguishing between S. epidermidis isolates from hospital and nonhospital sources can be challenging, but rapid single nucleotide polymorphism-based assays may help 6.
• S. epidermidis isolates are generally susceptible to linezolid, daptomycin, tigecycline, and quinupristin/dalfopristin, but may exhibit resistance to vancomycin 7.
• The choice of treatment for S. epidermidis infections depends on the severity of the infection, the presence of underlying medical conditions, and the susceptibility of the isolate to antimicrobial agents 3, 4, 7.