What is the organism responsible for bullous impetigo?

Organism Responsible for Bullous Impetigo

Bullous impetigo is primarily caused by toxin-producing strains of Staphylococcus aureus. 1, 2 This bacterial pathogen produces exfoliative toxins that specifically target desmoglein-1, a protein essential for cell adhesion in the upper epidermis, resulting in the characteristic bullous lesions.

Pathophysiology and Clinical Presentation

• Mechanism of disease: S. aureus produces exfoliative toxins that cleave the dermal-epidermal junction 2
• Lesion formation: The toxin action leads to the development of fragile, thin-roofed vesicopustules that rapidly enlarge to form flaccid bullae 1, 2
• Appearance: Initially clear yellow fluid fills the bullae, which later becomes darker, more turbid, and sometimes purulent 1
• Resolution: Bullae rupture, leaving crusted, erythematous erosions often surrounded by a collar of the roof's remnants 2

Epidemiology

• Represents approximately 30% of all impetigo cases 3, 4
• More common in children aged 2-5 years, but can affect individuals of any age 1
• More prevalent in warm, humid climates and areas with poor hygiene 2
• Usually affects exposed areas of the body, particularly the face and extremities 1

Diagnostic Considerations

• Diagnosis is primarily clinical based on the characteristic appearance of lesions 2
• Gram stain and culture of pus or exudates from skin lesions can help confirm the diagnosis 1
• While S. aureus is the predominant cause of bullous impetigo, rare cases caused by Group A Streptococcus have been reported 5

Treatment Implications

• The FDA has approved mupirocin ointment for the topical treatment of impetigo due to S. aureus 6
• According to IDSA guidelines, treatment options include:
  • Topical therapy: Mupirocin or retapamulin twice daily for 5 days 1
  • Oral therapy: For extensive disease, a 7-day regimen with an agent active against S. aureus (dicloxacillin or cephalexin for MSSA; doxycycline, clindamycin, or SMX-TMP for suspected MRSA) 1

Important Clinical Considerations

• While non-bullous impetigo can be caused by either S. aureus or Streptococcus pyogenes, bullous impetigo is almost exclusively caused by S. aureus 3
• Bullous impetigo represents the milder end of a spectrum that includes staphylococcal scalded skin syndrome, where toxins spread hematogenously 7
• Complications are rare, with the most serious being poststreptococcal glomerulonephritis (more commonly associated with streptococcal infections) 3
• Increasing prevalence of antibiotic-resistant strains, including methicillin-resistant S. aureus (MRSA), should be considered when selecting empiric therapy 3

Understanding that S. aureus is the primary causative organism of bullous impetigo guides appropriate antimicrobial selection and management strategies to effectively treat this common skin infection.