What is Exfoliative Toxin A (ETA)?

Exfoliative Toxin A (ETA): A Key Virulence Factor in Staphylococcal Skin Infections

Exfoliative Toxin A (ETA) is a specific serine protease produced by Staphylococcus aureus that causes epidermal cleavage at the granular layer of the skin, resulting in the characteristic exfoliation seen in staphylococcal scalded skin syndrome (SSSS). 1, 2

Characteristics and Mechanism of Action

• Structure and Function:

  • ETA is a 27-kDa zinc-dependent exotoxin produced by S. aureus
  • Acts as a serine protease that specifically targets desmoglein-1, a protein essential for cell-to-cell adhesion in the epidermis
  • Causes separation of cells at the zona granulosa layer, leading to blister formation and skin exfoliation

• Genetic Basis:

  • Encoded by the eta gene located on a temperate bacteriophage (ΦETA)
  • Often found alongside other toxin genes in pathogenic S. aureus strains 3
  • High prevalence (76.7%) of eta gene has been reported in clinical S. aureus isolates in some regions 3

Clinical Significance

Associated Conditions:

• Staphylococcal Scalded Skin Syndrome (SSSS):

  • Primarily affects infants and young children
  • Characterized by widespread skin exfoliation resembling scalding
  • All strains isolated from patients with generalized exfoliative syndrome or bullous impetigo produce ETA and/or ETB 1

• Bullous Impetigo:

  • Localized form of SSSS with fluid-filled blisters
  • Caused by the same exfoliative toxins but remains localized to the site of infection

Epidemiology:

• ETA is more common than ETB in most geographic regions
• Recent increases in SSSS incidence in North America have been attributed to migration and expansion of existing S. aureus lineages carrying ΦETA rather than new acquisition of the phage by different strains 4
• Multiple sequence types (STs) of S. aureus can carry eta, with ST109, ST15, ST121, and ST582 being most prevalent globally 4

Detection Methods

Several methods have been developed to detect ETA in clinical settings:

• PCR: Detects the eta gene directly from bacterial isolates
• Western Blot Analysis: Using specific antibodies against ETA
• F(ab')₂ fragment ELISA: Overcomes interference by staphylococcal protein A, allowing direct detection from serum samples in picogram amounts 5

Clinical Implications

• Early detection of ETA-producing S. aureus is crucial for proper diagnosis and management of SSSS
• Patients with suspected SSSS should be promptly treated with appropriate antibiotics to eliminate the toxin-producing bacteria
• The presence of ETA-producing strains in healthcare settings poses a significant risk, particularly in neonatal units where outbreaks have been reported 4

Prevention and Control

• Proper hand hygiene and infection control measures are essential to prevent transmission of ETA-producing S. aureus
• Healthcare workers should be screened during outbreaks to identify potential carriers
• Prompt isolation of affected patients can prevent spread in hospital settings

The high prevalence of eta genes in clinical isolates highlights the importance of surveillance and appropriate infection control measures, particularly for vulnerable populations such as infants, elderly, and immunocompromised patients 3.