Cutaneous Bacterial Infections
Primary bacterial infections are frequently caused by Staphylococcus aureus and Streptococcus pyogenes. Recognizing the depth and morphology of these lesions is vital for management.
Primary Superficial vs. Deep Infections
| Condition | Key Morphology | Pathogen |
|---|---|---|
| Impetigo | “Honey-colored” crusts | S. aureus / S. pyogenes |
| Ecthyma | Ulcerative, deep-seated crust | S. pyogenes |
| Folliculitis | Small, pus-filled follicular papules | S. aureus |
| Erysipelas | Raised, well-demarcated redness | S. pyogenes |
Clinical Pearls & Exam Focus
- Impetigo: Non-bullous is the most common form. Topical mupirocin is first-line; oral antibiotics are reserved for extensive cases.
- Erysipelas vs. Cellulitis: Erysipelas involves the superficial dermis and lymphatics (well-defined borders); Cellulitis involves the deeper dermis and subcutaneous fat (ill-defined borders).
High-Yield Exam Pearl:
- Scalded Skin Syndrome: Caused by S. aureus exfoliative toxins; involves separation at the stratum granulosum (not subepidermal).
- Strep vs. Staph: Always differentiate via history and lesion appearance; group A Strep remains the most common cause of erysipelas.