INFECTION OF THE SKIN

• Macules


  Flat lesions characterized by change in color of the affected skin
• Papules


  Raised lesions, solid in consistency of less than 5 mm in diameter
• Plaques


  Flat with elevated surface (plateau like) with more than 5 mm diameter
• Nodules


  Rounded raised lesions more than 5 mm in diameter
• Urticaria (wheals or hives)

  Annular or ring like papules or plaques with pinkish color
• Vesicles


  Circumscribed fluid filled lesions less than 5 mm in diameter
• Bullae


  Circumscribed fluid filled lesions more than 5 mm in diameter
• Pustules


  Circumscribed, exudate filled lesions
• Purpura


  Skin lesions due to bleeding into the skin

  
• Petechiae


  Less than 3 mm diameter
• Ecchymosis


  More than 3 mm diameter
• Ulcer


  Crater like lesion that may involve the deeper layers of the epidermis and dermis
• Eschar


  Necrotic ulcer covered with a blackened scab or crust
• Staphylococcus aureus


  • Common pathogen in humans
  • Gram positive cocci usually arranged individually, in pairs, short chains, or in grape like clusters
  • Found in the skin and the nasopharynx
  • Produces gray to golden yellow colonies, best at 20°C-25°C
  • Coagulase positive
  • Catalase positive
  • Produces enzymes and toxins responsible for its invasiveness and pathogenicity

  
• Folliculitis


  A pyogenic (pus producing) infection involving the hair follicle, characterized by localized painful inflammation and heals rapidly after draining the pus
• Furuncle


  An extension of folliculitis and is also known as boil, characterized by larger and painful nodules with underlying collection of dead and necrotic tissue
• Carbuncle


  Represents a coalescence of furuncles that extends into the subcutaneous tissue with multiple sinus tracts
• Sty or hordeolum


  Folliculitis occurring at the base of the eyelids
• Impetigo


  Infection is common in young children and primarily involves the face and the limbs, initially starts as a flattened red spot (macule) which later becomes a pus filled vesicle that ruptures and forms crust (honey colored crust), may be caused by both S. aureus and S. pyogenes

  
• Staphylococcal Scalded Skin Syndrome (Ritter's disease)

  Primarily a disease found in newborns and young children, manifested by sudden onset of perioral erythema (redness) that covers the whole body within two days, skin displacement with slight pressure (positive Nikolsky sign), bullae and cutaneous blister formation, desquamation, caused by exfoliative toxin

  
• Staphylococcus epidermidis


  Part of the normal flora of the skin, commonly associated with "stitch abscess," UTI, and endocarditis, also causes infections in individuals with prosthetic devices

  
• Streptococcus pyogenes


  • Gram positive cocci arranged in pairs or in chains, belongs to group A Streptococci, beta hemolytic, major virulence factor is M protein which is anti phagocytic, produces enzymes and toxins responsible for pathogenesis
• Pyoderma (Impetigo)


  A purulent skin infection that is localized and commonly involves the face, and the upper and lower extremities, starts as vesicles then progresses to pustules, the lesions rupture and form honey colored crusts, may have enlarged regional lymph nodes but no systemic infection

  
• Erysipelas (St. Anthony's Fire)


  Follows a respiratory tract or skin infection caused by S. pyogenes, patients manifest with localized raised areas associated with pain, erythema, and warmth, grossly distinct from normal skin, accompanied by lymphadenopathy and systemic manifestations
• Cellulitis


  Involves the skin and subcutaneous tissue, unlike erysipelas the infected and the normal skin are not clearly differentiated, manifested as local inflammation with systemic signs

  
• Necrotizing Fasciitis


  Involves the deep subcutaneous tissue and is also known as "flesh eating" or streptococcal gangrene, starts as cellulitis then becomes bullous and gangrenous, spreads to the fascia then the muscle and fat, may become systemic and cause multi organ failure leading to death
• Acute glomerulonephritis and rheumatic fever are non suppurative, immune mediated complications of streptococcal infections, acute glomerulonephritis is more commonly associated with skin infections while rheumatic fever is usually associated with S. pyogenes throat infection
• Pseudomonas aeruginosa


  • Gram negative bacilli arranged in pairs, encapsulated, capable of producing water soluble pigments (e.g., pyocyanin – blue), opportunistic pathogen, common cause of nosocomial infections, resistant to most antibiotics, virulence due to adhesins, toxins, and enzymes
• Pseudomonas aeruginosa skin infections

  Commonly associated with colonization of burn wounds and characterized by blue green pus that exudes a sweet grape like odor, other skin infections are folliculitis, and secondary infections in individuals with acne and nail infections resulting from immersion in contaminated water, most common cause of inflammation of the bone and cartilage of the foot called osteochondritis following a penetrating injury

  
• Clostridium perfringens


  • Gram positive bacilli that are anaerobic and rarely produce endospores, produces four lethal toxins (alpha, beta, iota, and epsilon), alpha toxin is the most lethal as it acts as a lecithinase that cause lysis of erythrocytes, platelets and leukocytes, widely distributed in nature and particularly associated with soil and water contaminated with feces
• Clostridium perfringens skin infections


  Causes soft tissue infections like cellulitis, suppurative myositis, and myonecrosis or gas gangrene, gas gangrene is a life threatening infection following physical trauma or surgery characterized by massive tissue necrosis with gas formation, shock, renal failure, and death within two days of onset

  
• Bacillus anthracis


  • Gram positive bacilli arranged individually or in pairs or long serpentine chains giving them the characteristic "bamboo fishing rod" or "Medusa head" appearance, aerobic, spore forming, and encapsulated, virulence due to polypeptide capsule and toxins (edematoxin and lethal toxin)

  
• Cutaneous anthrax


  The most common form of anthrax, characterized by painless papules at the site of inoculation that become ulcerative, and later develops necrotic eschar, associated with painful lymphadenopathy and edema
• Tinea versicolor (Pityriasis versicolor)


  Caused by Malassezia furfur (Pityrosporum orbiculare), a normal flora of the skin particularly in areas rich in sebaceous glands, lesions are irregular, discrete hypo or hyperpigmented macules depending on the skin color of the affected individual, lesions are scaly with a dry, chalky appearance, usually appear on the face, neck trunk, and arms

  
• Diagnosis of tinea versicolor is made by microscopic visualization of "spaghetti and meatballs" appearance

  
• Spores


  Only observed on culture in low carbon dioxide tension
• Demonstration of the spores

  Can be done using Dorner stain or Wirtz Conklin stain
• Antibiotics for treatment

  • Penicillin
  • Doxycycline
• Ciprofloxacin

  Recommended in resistant cases
• Prevention through vaccination of


  • Animals
  • Individuals at risk (animal handlers, veterinarians, military personnel, those working in slaughterhouses)