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

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