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
• Brown or black papules-are

  often melanocytic lesions.
• Red papules- are often

  vascular lesions.
• PLAQUES -flat with elevated surface (plateau-like)

  with more than 5 mm diameter
• NODULES -rounded raised lesions more than 5 mm in

  diameter

  • Usually extends into the dermis and

  subcutaneous tissue
• 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.

  • The fluid is visible as the lesions are translucent.
• BULLAE -circumscribed fluid-filled lesions

  more than 5 mm in diameter
• PUSTULES -circumscribed, exudate-filled lesions
• PURPURA -Extravasation of RBCs from

  cutaneous vessels in the skin and

  mucous membranes:
• PURPURA-• a. Petechiae – less than 3 mm

  diameter

  • b. 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
• Staphylococci: Staphylococcus

  aureus - Common

  pathogen in

  humans

  They are gram-positive

  cocci usually arranged

  individually, in pairs,

  short chains, or in

  grape-like clusters
• where is S. aureus commonly found?

  skin and the nasopharynx.
• Golden yellow

  colonies of S.aureus are best

  produced when cultured

  at 20 °C–25 °C.
• what is the mode of transmission of S. aureus?


  Direct contact
• Folliculitis – a pyogenic (pus-producing)

  infection involving the hair follicle. It is

  characterized by localized painful inflammation

  and heals rapidly after draining the pus.
• Furuncle – an extension of folliculitis and is

  also known as boil. It is 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

  • primarily involves the face and the limbs

  • Initially it starts as a flattened red spot (macule) which

  later becomes a pus-filled vesicle that ruptures and forms

  crust (honey-colored crust).

  • It 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.

  •It is manifested by sudden onset of perioral erythema (redness) that

  covers the whole body within two days.
• positive Nikolsky sign - When slight pressure is applied over the skin, it causes displacement

  of the skin
• Antibodies against the exfoliative toxin are produced within 7 to 10

  days enabling the skin to become intact again.
• what is The toxin responsible for these manifestations of ritter's disease?

  exfoliative toxin.
• Only the outer layer of the epidermis is affected hence there will be

  no scarring
• Treatment of choice of S. aureus: beta-lactam antibiotics like penicillin
• Oxacillin is the only penicillin-derived antibiotic that has

  remained active against S. aureus.
• Staphylococcus epidermidis - part of the normal flora of the skin .

  commonly associated with “stitch abscess,” UTI, and

  endocarditis.

  It also causes infections in individuals with prosthetic device.
• Streptococci: Streptococcus pyogenes - gram-positive cocci arranged in pairs or in chains when

  seen under the microscope.
• It belongs to group A Streptococci based on Lancefield

  classification.
• Its major virulence factor is M protein which is anti-

  phagocytic.
• True or False?


  S. pyogenes is a beta hemolytic (cause complete hemolysis of blood).
• What is the mode of transmission of S. pyogenes?

  direct contact with infected persons or through fomites.
• Pyoderma

  (Impetigo) - a purulent

  skin infection that is

  localized and

  commonly involves

  the face, and the

  upper and lower

  extremities.
• Erysipelas (St. Anthony’s Fire) – follows a respiratory tract or

  skin infection caused by S. pyogenes.
• Cellulitis - involves the skin and subcutaneous tissue. Unlike erysipelas,

  the infected and the normal skin are not clearly differentiated. It is also manifested as local inflammation with systemic signs.
• Necrotizing Fasciitis – involves the deep subcutaneous tissue and is also known as “flesh-eating” or streptococcal gangrene.