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