Skip to main content
Biology LibreTexts

15.1C: Bacterial Skin Diseases

  • Page ID
    12106
  • Bacterial skin infections include impetigo, erysipelas, and cellulitis.

    LEARNING OBJECTIVES

    Describe how impetigo, erysipelas and cellulitis are acquired and the treatment options available

    KEY TAKEAWAYS

    Key Points

    • Impetigo is a highly contagious bacterial skin infection most common among pre-school children primarily caused by Staphylococcus aureus and sometimes by Streptococcus pyogenes.
    • Erysipelas is an acute streptococcus bacterial infection of the upper dermis and superficial lymphatics.
    • Cellulitis is a diffuse inflammation of connective tissue with severe inflammation of dermal and subcutaneous layers of the skin.
    • Antimicrobial therapy is available for impetigo, erysipelas, and cellulitis.

    Key Terms

    • erysipelas: a severe skin disease caused by streptococcus infection in surface and surrounding tissue, marked by continued spreading inflammation
    • impetigo: a contagious bacterial skin disease forming pustules and yellow crusty sores, chiefly on the face and hands. It is common in children. Infection is often through cuts or insect bites.
    • cellulitis: an inflammation of subcutaneous or connective tissue caused by a bacterial infection
    Figure: Facial impetigo.

    Common Bacterial Skin Infections

    Bacterial skin infections include impetigo, erysipelas, and cellulitis.

    IMPETIGO

    Impetigo is a highly contagious bacterial skin infection most common among pre-school children. It is primarily caused by Staphylococcus aureus and sometimes by Streptococcus pyogenes. The infection is spread by direct contact with lesions or with nasal carriers. The incubation period is 1–3 days. Dried streptococci in the air are not infectious to intact skin. Scratching may spread the lesions. Impetigo generally appears as honey-colored scabs formed from dried serum and is often found on the arms, legs, or face . For generations, the disease was treated with an application of the antiseptic gentian violet. Today, topical or oral antibiotics are usually prescribed.

    Figure: Facial erysipelas. Erysipelas of the face due to invasive Streptococcus.

    ERYSIPELAS

    Erysipelas is an acute streptococcus bacterial infection of the upper dermis and superficial lymphatics. This disease is most common among the elderly, infants, and children. People with immune deficiency, diabetes, alcoholism, skin ulceration, fungal infections, and impaired lymphatic drainage (e.g., after mastectomy, pelvic surgery, bypass grafting) are also at increased risk. Patients typically develop symptoms including high fevers, shaking, chills, fatigue, headaches, vomiting, and general illness within 48 hours of the initial infection. The erythematous skin lesion enlarges rapidly and has a sharply demarcated raised edge. It appears as a red, swollen, warm, hardened and painful rash, similar in consistency to an orange peel. More severe infections can result in vesicles, bullae, and petechiae, with possible skin necrosis. Lymph nodes may be swollen and lymphedema may occur. Occasionally, a red streak extending to the lymph node can be seen. Most cases of erysipelas are due to Streptococcus pyogenes (also known as beta-hemolytic group A streptococci), although non-group A streptococci can also be the causative agent. Beta-hemolytic, non-group A streptococci include Streptococcus agalactiae, also known as group B strep or GBS. Depending on the severity, treatment involves either oral or intravenous antibiotics, using penicillins, clindamycin, or erythromycin. While illness symptoms resolve in a day or two, the skin may take weeks to return to normal.

    Figure: Cellulitis. Left shin infected with cellulitis.

    CELLULITIS

    Cellulitis is a diffuse inflammation of connective tissue with severe inflammation of dermal and subcutaneous layers of the skin. Cellulitis can be caused by normal skin flora or by exogenous bacteria, and often occurs where the skin has previously been broken. Common points of infection include cracks in the skin, cuts, blisters, burns, insect bites, surgical wounds, intravenous drug injection, or sites of intravenous catheter insertion. Group A Streptococcus and Staphylococcus are the most common of these bacteria, which are part of the normal flora of the skin, but normally cause no actual infection while on the skin’s outer surface. Skin on the face or lower legs is most commonly affected by this infection, though cellulitis can occur on any part of the body. The mainstay of therapy remains treatment with appropriate antibiotics Recovery periods last from 48 hours to six months. The typical signature symptom of cellulitis is an area which is red, hot, and tender . Cellulitis is most often a clinical diagnosis, and local cultures do not always identify the causative organism. Blood cultures usually are positive only if the patient develops generalized sepsis.Treatment consists of resting the affected area, cutting away dead tissue, and administration of antibiotics (either oral or intravenous).