- Coagulase-negative staphylococci (CoNS) normally colonize skin, more heavily in occluded than nonoccluded sites (axillae, anogenitalia)
- Erythrasma, pitted keratolysis, trichomycosis, and infectious intertrigo are common superficial cutaneous infections
- Staphylococcus aureus colonizes the nares and intertriginous skin intermittently, can penetrate the stratum corneum, and can cause infection, e.g., impetigo, folliculitis
- Methicilllin-resistant S. aureus (MRSA) has become an important pathogen for community-acquired (CA-MRSA) and health care-acquired (HA-MRSA) infections
- Erythrasma: intertriginous sites of webspaces of feet, groins, axillae
- Pitted keratolysis: plantar feet and webspaces of feet
- Trichomycosis: axillae, pubis
- S. aureus and group A streptococcus (GAS) cause cutaneous infections and systemic intoxications
- Etiology: overgrowth of normal flora at sites of skin occlusion
- Normal skin is heavily colonized by bacterial flora (harmless commensals) such as coagulase negative staphylococci (CoNS). Colonization is more dense in intertriginous and occluded sites.
- Pathogens Staphylococcus aureus and, less commonly, group A β-hemolytic streptococcus (GAS) (Streptococcus pyogenes) colonize, and infect the skin. They cause a variety of syndromes, including skin and soft tissue infections (SSTIs), bacteremia, and systemic intoxications. An intact stratum corneum is the most important defense against invasion of pathogenic bacteria.
- Predispositon to infection:
- Chronic S. aureus carrier state (nares, axillae, perineum, vagina)
- Warm weather/climate, high humidity
- Skin disease, especially atopic dermatitis, familial pemphigus
- Social situation: poor hygiene, crowded living conditions, neglected minor trauma
- Chronic disease: obesity, diabetes mellitus, HIV/AIDS, especially MRSA infection, solid organ transplant recipient, iatrogenic immunosuppression
- Immunodeficiency: cancer chemotherapy, bactericidal defects (e.g., chronic granulomatous disease), chemotactic defects, hyper-IgE syndrome (Job syndrome)
- Coagulase negative staphylococci (CoNS), colonizing the skin shortly after birth, have been subdivided into 32 species, 15 of which are indigenous to humans. The most common CoNS are S. epidermidis (65–90% of individuals), S. hominis. S. haemolyticus,S. warneri, and S. lugdunensis. CoNS have lower pathogenicity in the skin and mucosa but increasingly cause infection of artificial devices such as percutaneous intravenous catheter (PIC) lines and heart valves.
- Group A streptococcus (GAS) usually colonizes the skin first and then the nasopharynx. Group B (Streptococcus agalactiae) and group G β-hemolytic streptococci (GBS, GGS) colonize the perineum of some individuals and may cause superficial and invasive infections.
- S. aureus does not normally reside on human skin (not one of the normal resident flora), but may be present transiently, inoculated from colonized sites such as the nares. Colonization and infection follow contact with shedding human lesions, fomites contaminated from these lesions, and human respiratory tract and skin. The nares of pets can also be colonized. S. aureus of mucous membranes of the anterior nasopharynx (nares) of 30% of otherwise healthy persons; other commonly colonized sites include axillae, vagina (5–15%; up to 30% during menses), damaged skin, perineum. Colonization is usually intermittent; 10–20% of individuals have persistent colonization; 10–20% are never colonized. Colonization rates higher among health care workers, dialysis patients, patients with type 1 diabetes, injection drug users, persons with HIV/AIDS disease, those with ...
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