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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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