Skin Microflora and Infection Risk

• Normal microflora, or microbiome, refers to the microbial population colonizing the human body.
• Colonization can be permanent or transient, lasting only hours or days.
• Microorganisms are typically non-pathogenic in their usual location; disease occurs if introduced to sterile sites.

Skin Microflora

• Gram-positive bacteria include coagulase-negative staphylococci (e.g., S. epidermidis, S. hominis), Corynebacterium spp., Propionibacterium spp., Micrococcus spp., Staphylococcus aureus (carrier state), and Streptococcus pyogenes (carrier state).
• Gram-negative bacteria include Acinetobacter spp. and, rarely, Escherichia coli, which is transient due to dry skin.
• Fungi include Candida spp. and Malassezia spp.

Risk Factors for Skin Infections

• Changes in skin microbiota influence infection risk.
• Being a carrier of Staphylococcus aureus or Streptococcus pyogenes increases risk.
• Traumas such as burns, fractures, bites, and stings are risk factors.
• Surgical wounds raise infection risk.
• Diabetes and AIDS elevate susceptibility to skin infections.

Folliculitis

• Folliculitis is a minor pyogenic infection of hair follicles.
• Staphylococcus aureus is the most common causative agent.
• Pseudomonas aeruginosa is common, especially in hot tubs.
• Candida albicans is a cause in immunocompromised hosts.
• Common sites are the neck, face, axillae, and buttocks.
• A complication at the eyelid is a stye.
• Treatment includes drainage and topical or systemic antibiotics like aminoglycosides, tetracyclines, macrolides, lincosamides, and mupirocin.

Furuncle (Boils)

• Furuncles are an extension of folliculitis into deeper tissues.
• Symptoms include a large, painful, raised nodule with necrotic tissue.
• It can drain spontaneously or with surgical incision.
• Staphylococcus aureus is the cause.
• A solitary furuncle is simply called a furuncle.
• Furunculosis involves multiple furuncles and can be recurrent.
• Extension to the dermis and subcutaneous tissue can result in carbuncle formation.
• Treatment is drainage + antibiotics like mupirocin, cloxacillin, clindamycin, cefadroxil, and macrolides.

Carbuncle

• Carbuncles are a cluster of furuncles extending to the dermis and subcutaneous tissue.
• Symptoms can include fever and chills, indicating bacteremia.
• Staphylococcus aureus is the causative agent.
• Surgical drainage and antibiotics are required.

Acne Vulgaris

• Acne Vulgaris is inflammation of hair follicles and their associated sebaceous glands.
• Propionibacterium acnes, Corynebacterium spp., and Brevibacterium spp. are causes.
• Linked to hormonal changes affecting sebum secretion at puberty.
• It typically resolves in early adult life.
• Treatment options include drainage of lesions and antibiotics such as macrolides, tetracyclines, and clindamycin.

Infection of Keratinized Layers

• Dermatophytosis: Fungal infections of skin, hair, and nails.
• Commonly called ringworm.
• Caused by dermatophyte fungi, the only organisms that can use keratin.