Bacterial Skin Infections in Patients with Darker Skin

Corynebacteria are gram-positive, club-shaped bacilli. Corynebacteria are commonly isolated on tellurite or Loeffler's media and have characteristic metachromatic granules. The major pathogenic species is Corynebacterium diphtheriae, which causes diphtheria—a severe upper respiratory infection. The characteristic findings of diphtheria include pharyngeal pseudomembranes (grayish tonsillar exudates), severe pharyngitis, and “bull’s neck” lymphadenopathy. Treatment is primarily through passive immunization with antitoxin and antibiotics. Prevention is via the diphtheria toxoid vaccine.

Cellulitis is a common infection caused by bacteria that affects the dermis and subcutaneous tissue of the skin. It is frequently caused by Staphylococcus aureus and Streptococcus pyogenes. The skin infection presents as an erythematous and edematous area with warmth and tenderness. The borders are not clearly delineated. The lower extremities are the most frequent site of infection, but cellulitis can occur anywhere on the body. Diagnosis is usually clinical, and management involves oral and/or parenteral antibiotics. Coverage for MRSA may be added, depending on the presence of risk factors.

Staphylococcal scalded skin syndrome (SSSS), also known as Ritter disease and staphylococcal epidermal necrolysis, is a toxin-mediated condition caused by Staphylococcus aureus. The exfoliative toxin produced disseminates and cleaves desmoglein 1 in the epidermis, causing separation and detachment of the skin. SSSS most commonly affects young children. Prodromal symptoms precede diffuse cutaneous erythema, tenderness, bullae formation, and superficial desquamation. The mucous membranes are spared. The diagnosis is made clinically and can be confirmed with culture data (targeting possible primary infection sites) and biopsy. However, cultures of bullae are not useful. Antibiotics and supportive care should be initiated as soon as the diagnosis is suspected.

Mycobacterium is a genus of the family Mycobacteriaceae in the phylum Actinobacteria. Mycobacteria comprise more than 150 species of facultative intracellular bacilli that are mostly obligate aerobes. Mycobacteria are responsible for multiple human infections including serious diseases, such as tuberculosis (M. tuberculosis), leprosy (M. leprae), and M. avium complex infections. While lungs are the most common site of infection, mycobacteria can colonize and infect other organ systems including the lymph nodes, skin, sinuses, eyes, ears, bones, CNS, and urinary tract.

Syphilis is a bacterial infection caused by the spirochete Treponema pallidum pallidum (T. p. pallidum), which is usually spread through sexual contact. Syphilis has 4 clinical stages: primary, secondary, latent, and tertiary. Primary syphilis begins with a chancre, a painless ulcer on the genitals. Progression to secondary syphilis manifests as a generalized maculopapular rash, which includes the palms and soles. The development of tertiary syphilis can cause severe neurologic (neurosyphilis), cardiovascular, and/or gummatous disease. The diagnosis is through both treponemal and nontreponemal testing. Penicillin G is the antibiotic of choice. The duration of management varies based on the stage of the disease.

Erysipelas is a bacterial infection of the superficial layer of the skin extending to the skin's superficial lymphatic vessels. This infection presents as a raised, well-defined, tender, and bright red rash. Typically on the legs or face, but erysipelas can occur anywhere on the skin. This infection occurs when bacteria enter through the points of skin breakdown. The most common bacteria causing this infection is group A Streptococci (especially Streptococcus pyogenes). Diagnosis is based mostly on the history and physical exam. Management includes antibiotics.

Impetigo is a highly contagious superficial bacterial infection typically caused by Staphylococcus aureus (most common) and Streptococcus pyogenes. Impetigo most commonly presents in children aged 2 to 5 years with lesions that evolve from papules to vesicles to pustules, which eventually break down to form characteristic “honey-colored” crusts. Infection can either be primary (bacterial infection of healthy, intact skin) or secondary (infection of pre-existing abrasions). The diagnosis is clinical, and management includes topical or systemic antibiotic therapy. Complications of impetigo include post-streptococcal glomerulonephritis, cellulitis, and scarlet fever.

Infectious folliculitis is a common skin condition characterized by the inflammation of hair follicles caused by an infectious agent (bacterial, fungal, viral, or parasitic). Staphylococcus aureus is the most common causative agent. Diagnosis is clinical and presentations include pruritus, follicular pustules, and erythematous papules. Management is usually supportive care but topical or oral antibiotic therapy may be required in severe cases.

Bacteriology is the branch of microbiology that deals with the morphology, structure, classification, and biochemistry of bacteria. The discipline of bacteriology arose during the 19th century from scientific attempts to prove the “germ theory of disease,” namely that diseases were caused by microscopic organisms invading host cells. Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Management of bacterial disease is generally with antibiotics; however, the choice of antibiotics may vary depending on the bacterial structure and metabolism.