Bacterial infection – Staphylococcal and streptococcal
The skin is a barrier to infection but, if its defences are penetrated or broken down, numerous micro-organisms can cause disease (Table 1).
Table 1 Bacterial diseases of the skin
| Organism | Infection |
|---|---|
| Commensals | Erythrasma, pitted keratolysis, trichomycosis axillaris |
| Staphylococci | Impetigo, ecthyma, folliculitis, secondary infection |
| Streptococci | Erysipelas, cellulitis, impetigo, ecthyma, necrotizing fasciitis |
| Gram-negative | Secondary infection, folliculitis, cellulitis |
| Mycobacterial | TB (lupus vulgaris, warty tuberculosis, scrofuloderma), fish tank granuloma, Buruli ulcer, leprosy |
| Spirochaetes | Syphilis (e.g. primary, secondary), Lyme disease (erythema chronicum migrans) |
| Neisseria | Gonorrhoea (pustules), meningococcaemia (purpura) |
| Others | Anthrax (pustule), erysipeloid (pustule) |
Staphylococcal infections
Impetigo
Clinical presentation
Impetigo is now relatively uncommon in the UK, mainly because of improved social conditions, but it is endemic in developing countries. It generally occurs in children and presents as thin-walled, easily ruptured vesicles, often on the face, which leave areas of yellow-crusted exudate (Fig. 1). Lesions spread rapidly and are contagious. A bullous form, with blisters 1–2 cm in diameter, is seen in all ages and affects the face or extremities. Atopic eczema, scabies, herpes simplex and lice infestation may all become impetiginized. Impetigo can be confused with herpes simplex or a fungal infection.
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