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Skin infections

Bacterial infections key points test

Impetigo is due to superficial skin infection with: *! Staphylococcus aureus * Streptococcus mutans * Diptheroids * Staphylococcus epidermidis Explanation: Impetigo is a superficial skin infection with _Staphylococcus aureus_ and/or _Streptococcus pyogenes_. Diptheroids occasionally cause skin infection (erythrasma and pitted keratolysis). _S. epidermidis_ may be responsible for some minor inflammatory skin conditions such as miliaria. S. mutans is the intraoral species responsible for dental caries. Erysipelas may be due to superficial skin infection with: * Erysipelothrix rhusiopathiae *! Streptococcus pyogenes * Diptheroids * Staphylococcus epidermidis Explanation: Erysipelas and cellulitis are nearly always due to Streptococcus pyogenes, and rarely by S. aureus, enterobacteriae and anaerobes. Erysipelothrix rhusiopathiae is the organism responsible for erysipeloid, which is very rare. Impetigo rarely (<1%) complicates: * Traumatic wounds * Infestations * Atopic dermatitis *! Acne Explanation: Impetigo complications traumatic wounds, infestations and atopic dermatitis quite commonly but is rare in acne (except in those treated with oral isotretinoin). Furunculosis (boils) is due to invasion of the hair follicle by: *! Staphylococcus aureus * Streptococcus pyogenes * Diptheroids * Staphylococcus epidermidis Explanation: Furunculosis is due to Staphylococcus aureus. Staphylococcal skin infections may rarely be complicated by widespread rashes including: * Pityriasis rubra pilaris * Necrotising fasciitis *! Toxic shock syndrome * Guttate psoriasis Explanation: Widespread rashes caused by staphylococcal skin infection are toxic shock syndrome, staphylococcal scalded skin syndrome and staphylococcal scarlatina. Psoriasis can be precipitated by streptococcal infection (usually tonsillitis). Necrotising fasciitis is life-threatening full-skin thickness necrosis most often caused by Group A haemolytic streptococcus. Pityriasis rubra pilaris is not thought to be due to infection. Streptococcal skin infections may rarely be complicated by widespread rashes including: * Lichen planus *! Scarlatina * Scalded skin syndrome * Varicella Explanation: Scarlatina, or scarlet fever, is due to a specific strain of streptococcus. Scalded skin syndrome is staphylococcal. Varicella is due to herpes zoster virus. Lichen planus is not thought to be due to infection.