Human Microbiota & Microbiome – Exam Review Notes
Learning Objectives
- Define microbiota vs microbiome
- Locate major body sites harbouring microbiota
- Summarise benefits & disease potential of the microbiome
Key Definitions
- Microbiota: complete set of microorganisms living on/within a host
- Microbiome: collective genome of the microbiota (terms often used interchangeably)
Usual Body Sites & Representative Organisms
- Skin
- Mouth & upper respiratory tract
- Gastrointestinal tract (highest density in colon)
- Genitourinary tract (distal regions)
- Internal tissues, blood, cerebrospinal fluid, peritoneal cavity remain sterile under normal conditions
Relationship to Host
- Generally mutualistic or commensal
- Can turn parasitic when:
• Microbes enter sterile sites (e.g., bowel perforation, wounds, invasive hospital procedures)
• Community balance shifts (pH change, immunosuppression, broad-spectrum antibiotics)
- Mode of birth (vaginal vs caesarean)
- Infant feeding (breast vs formula)
- Age & developmental stage
- Diet & geography (high- vs low-income regions)
- Environment & medications
Core Microbiome Concept
- Species present at a given body site in ≥ ninety-five percent of healthy individuals
Germ-Free (Axenic) Animal Findings
- Longer lifespan in sterile environments (no dental disease)
- Poorly developed immune system; high mortality upon environmental exposure
- Altered gastrointestinal motility
Significance
- Aids digestion, vitamin synthesis, immune maturation, colonisation resistance
- Dysbiosis linked to infections and systemic disease
Further Reading
- Mim’s Medical Microbiology & Immunology, seventh edition, chapter nine