Topic 20: Bacteria of the Skin

  • The skin is generally an inhospitable environment for most microorganisms.
    • dry layers of keratin-containing cells that make up the epidermis are not easily colonized by most microbes
    • sebum (secreted by oil glands) inhibits bacterial growth
    • salt in perspiration create a hypertonic environment
    • perspiration and sebum are nutritive for certain microorganisms - normal microbiota of the skin
  • Normal microbiota of the skin tend to be resistant to drying and to relatively high salt concentrations
    • more bacteria are found in moist areas, axilla (armpit) and sides of the nose, than the dry surfaces
  • Transient microbiota are present on hands and arms in contact with the environment
  • Proprionibacterium live in hair follicles on sebum from oil glands
    • produce propionic acid that maintains the pH of the skin between 3-5
    • this acidicity suppresses the growth of other bacteria
  • Most bacteria on the skin are gram-positive and salt-tolerant
  • Staphylococcus aureus is a member of the normal microbiota of the skin and is also considered a pathogen.
    • produces coagulase, enzyme that coagulates the fibrin in blood, is pathogenic
    • presence of coagulase is used to distinguish S. aureus from other species of staphylococcous