What is Staphylococcus epidermidis?

Staphylococcus epidermidis: A Commensal Organism and Opportunistic Pathogen

Staphylococcus epidermidis is a permanent member of the normal human microbiota commonly found on skin and mucous membranes that can become an important opportunistic pathogen, particularly in healthcare settings when it colonizes medical devices and forms biofilms. 1

Characteristics and Natural Habitat

• S. epidermidis is a Gram-positive cocci that establishes a lifelong commensal relationship with humans beginning early in life by adhering to tissue surface moieties via specific adhesins 1
• It is ubiquitously found on human skin and mucous membranes, serving as part of the normal microflora 2
• As a commensal organism, S. epidermidis may provide benefits to the human host, including competing with more virulent pathogens 1

Pathogenicity and Virulence Factors

• Unlike Staphylococcus aureus, S. epidermidis lacks many of the major virulence factors and toxins, relying instead on different mechanisms for pathogenicity 3
• The primary virulence mechanism is its ability to form biofilms on implanted medical devices 3, 1
• Biofilm formation occurs in several stages:
  • Initial attachment to device surfaces through physicochemical properties (hydrophobicity, surface tension, electrostatic charge) 3
  • Adherence to host matrix proteins (fibrinogen, fibronectin, collagen) that coat implanted biomaterials 3
  • Production of polysaccharide intercellular adhesin that mediates cell-to-cell adhesion 3
  • Formation of an extracellular polymeric matrix that encases the bacterial community 3
• Bacteria within biofilms are more resistant to antibiotics and host defenses due to the protective extracellular matrix 3

Clinical Significance and Associated Infections

• S. epidermidis has emerged as an important opportunistic pathogen, particularly in healthcare settings 4, 1
• It is a common cause of:
  • Device-related infections, including cardiovascular implantable electronic device infections 3
  • Orthopedic device-related infections (causing approximately 20% of all cases, increasing to 50% in late-developing infections) 1
  • Surgical wound infections 4
  • Primary bacteremia, especially in immunocompromised patients 4, 5
• S. epidermidis infections are often indolent compared to other bacterial infections, with low levels of pro-inflammatory cytokines and high levels of interleukin-10, contributing to their sub-acute and persistent nature 1
• Isolation from blood cultures may represent either contamination during collection or true bacteremia, creating diagnostic challenges 2

Antimicrobial Susceptibility and Treatment

• S. epidermidis isolates from nosocomial infections frequently demonstrate resistance to methicillin 4
• Treatment options include:
  • For methicillin-sensitive strains: penicillin G, semisynthetic penicillinase-resistant penicillins, and cephalosporins 4
  • For methicillin-resistant strains: vancomycin is the drug of choice, often combined with rifampin or gentamicin for serious infections 4
• Management of device-related infections typically requires both antimicrobial therapy and removal of the infected device 4, 5

Diagnostic Challenges

• The occult nature of S. epidermidis infections and the low virulence of the organism make diagnosis and treatment difficult 4
• No reliable phenotypic or genotypic algorithms currently exist to predict the pathogenicity of S. epidermidis bloodstream infections 2
• Distinguishing between contamination and true infection remains challenging when S. epidermidis is isolated from blood cultures 2