Microbiology · MU Sofia

104. Role of Human Microbiota: Physiological & Harmful Effects, Iatrogenic

Covers the beneficial roles of the human microbiota, including barrier protection, immune modulation, metabolic functions such as short-chain fatty acid production, and the gut-brain axis. It then turns to harmful effects like dysbiosis and opportunistic infections, set out in a table of organisms and the diseases they cause. Iatrogenic influences from antibiotics, chemotherapy, immunosuppressants, medical devices and surgery are followed by a closing section on clinical prevention.

Inside: 6 sections · 3 labelled pictures · 1 table · 15 flashcards · 3 min

Topic 104 of 113 in the MU Sofia syllabus for Microbiology (Dental Medicine, Year 2). The free AceMed note covers it in 6 sections, about 336 words (3 min of reading), with 15 flashcards.

In this note

  1. Role of Human Microbiota: Physiological & Harmful Effects, Iatrogenic Influences, Opportunistic Infections
  2. I. Overview of Human Microbiota
  3. II. Physiological (Beneficial) Roles
  4. III. Harmful Effects of Microbiota
  5. IV. Iatrogenic Influences on the Microbiota
  6. V. Clinical Relevance & Prevention

I. Overview of Human Microbiota

  • Human microbiota refers to all microorganisms (bacteria, fungi, viruses, archaea) that colonize various surfaces of the body.
  • These microbes have evolved with the host and are critical for homeostasis, defense, and metabolism.
  • Composition differs by site (gut, skin, vagina, oral cavity, respiratory tract).

II. Physiological (Beneficial) Roles

1. Barrier Protection

  • Prevents colonization by pathogens through:
  • Competitive exclusion (nutrients, space)
  • Production of bacteriocins, organic acids
  • Maintenance of tight epithelial junctions

2. Immune System Modulation

  • Promotes mucosal immunity, development of GALT.
  • Stimulates production of secretory IgA
  • Trains immune system to tolerate commensals while attacking pathogens.

3. Metabolic Functions

  • Ferments indigestible carbohydrates → Short-chain fatty acids (SCFAs: acetate, butyrate)
  • SCFAs = energy source for colonocytes; anti-inflammatory properties
  • Synthesis of vitamins: e.g., K, biotin, B12
  • Assists in bile acid metabolism, drug metabolism

4. Neurological Impact (Gut–Brain Axis)

  • Gut microbes produce neuroactive substances: GABA, serotonin
  • Influence mood, behavior, stress response

III. Harmful Effects of Microbiota

1. Dysbiosis

  • Imbalance or loss of normal microbiota due to disease, diet, or drugs
  • Can lead to:
  • Inflammatory bowel diseases
  • Obesity, metabolic syndrome
  • Colon cancer
  • Autism spectrum disorder (hypothesized)

2. Opportunistic Infections

  • Normal flora can cause disease when:
  • Host immunity is low (AIDS, chemotherapy)
  • Barriers are breached (trauma, surgery)
  • Microbiota is altered (e.g., antibiotics)

Examples:

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