MM - LU6

Normal Microbiota of the Body

  • Healthy Internal Tissues:

    • Areas such as the brain, blood, cerebrospinal fluid, and muscles are typically devoid of microorganisms (microorgs).

  • Surface Tissues:

    • Tissues like skin and mucous membranes are continually exposed to microorgs and are easily colonized.

  • Normal Microbiota Definition:

    • Refers to a diverse mixture of microorganisms, primarily bacteria, found regularly at specific anatomical sites in the body, with fewer fungi and protozoa.

Importance of Understanding Normal Human Microbiota

  • Infection Insights:

    • Identifying specific locations of microorganisms can provide clues about potential infections.

  • Source and Significance:

    • Understanding what types of microorgs are isolated from infection sites can inform investigators about their origins and importance.

  • Growth Implications:

    • Awareness of the causes and consequences of the growth of microorgs typically absent from specific body sites can be gained.

  • Immune Response Role:

    • Recognizing the contribution of normal microbiota in stimulating host immune responses, which provide protection against pathogens.

Distribution of Normal Microbiota

  • Major Symbiotic Relationships:

    • Commensalism:

      • One organism benefits while the host remains unharmed.

    • Mutualism:

      • Both the symbiont and host benefit from the relationship.

    • Parasitism:

      • One organism benefits at the expense of the host.

  • Types of Associations:

    • Ectosymbiosis:

      • One organism exists outside another.

    • Endosymbiosis:

      • One organism resides within another.

Skin Microbiota

  • Epidermis Characteristics:

    • The skin presents an unfavorable environment for microbial colonization due to dryness and moisture variability.

    • High moisture areas (scalp, ears, anal regions, palms) support microbial life.

    • Slightly acidic nature (due to oils and sweat) discourages the growth of many microbes.

    • Hyperosmotic conditions from sodium chloride in sweat create stress for most microorganisms.

Factors Controlling Skin Microbiota

  • Bactericidal Substances:

    • The skin secretes substances that inhibit microbial colonization, control overgrowth, and reduce infections.

  • Skin Bacteria Locations:

    • Most bacteria colonize dead skin cells or areas near oil and sweat glands, which provide nutrients (water, amino acids, urea, electrolytes, fatty acids) for microbial growth, particularly Staphylococcus epidermidis.

  • Yeasts:

    • Commonly found on the scalp (e.g., Pityrosporum ovale).

  • Fungi:

    • Can cause conditions like athlete’s foot and ringworm.

  • Acne-Causing Bacteria:

    • Propionibacterium acnes is prevalent in skin glands and linked to acne development.

Respiratory Tract Microbiota

  • Microbial Presence:

    • The upper and lower respiratory tracts (including trachea, bronchi, bronchioles, and alveoli) are devoid of normal microbiota.

  • Microorg Removal Mechanisms:

    • Continual removal of microorganisms occurs through:

      • Mucus Stream:

        • Generated by ciliated epithelial cells.

      • Phagocytic Action:

        • Alveolar macrophages help eliminate potential pathogens.

      • Bactericidal Effects:

        • Lysozyme in nasal mucus acts to kill bacteria.