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we are more microbial than human

 

MICROBIOME OF THE HUMAN BODY



Your body is host to trillions of microorganisms — bacteria, viruses, fungi, and archaea — collectively called the human microbiome. They live in different niches (skin, gut, mouth, etc.) and perform critical functions. Here's a list by body part:

🧠 1. Mouth (Oral Cavity)

  • Major Microbes: Streptococcus, Veillonella, Actinomyces, Fusobacterium, Porphyromonas

  • Functions:

    • Begin digestion (breaking down sugars).

    • Prevent colonization by harmful pathogens.

    • Maintain oral immune balance.

    • Aid in nitric oxide production (via nitrate-reducing bacteria).

🫁 2. Nose & Respiratory Tract

  • Major Microbes: Staphylococcus epidermidis, Corynebacterium, Prevotella, Dolosigranulum

  • Functions:

    • Block respiratory pathogens.

    • Modulate local immunity.

    • Train immune system to tolerate harmless particles.

🧴 3. Skin

  • Major Microbes: Staphylococcus epidermidis, Propionibacterium acnes, Corynebacterium, Malassezia (fungus)

  • Functions:

    • Protect against skin infections.

    • Maintain skin pH and moisture.

    • Educate immune cells.

    • Produce antimicrobials.

🧬 4. Gut (Intestines) – Largest Microbial Habitat

  • Major Microbes: Bacteroides, Firmicutes (like Lactobacillus, Clostridium), Escherichia, Akkermansia, Methanobrevibacter

  • Functions:

    • Digest fiber to produce short-chain fatty acids (SCFAs).

    • Synthesize vitamins (B12, K).

    • Protect gut lining.

    • Prevent pathogen overgrowth.

    • Modulate systemic immunity.

    • Influence brain (gut-brain axis).

👃 5. Ears

  • Major Microbes: Similar to nearby skin and nose flora – Staphylococcus, Corynebacterium, Streptococcus

  • Functions:

    • Compete with invaders that can cause ear infections.

    • Maintain earwax pH balance.

👀 6. Eyes (Conjunctiva)

  • Major Microbes: Staphylococcus epidermidis, Corynebacterium, Pseudomonas

  • Functions:

    • Prevent pathogen invasion.

    • Help modulate local immune responses in a delicate, immune-privileged environment.

👃‍🦰 7. Hair & Scalp

  • Major Microbes: Cutibacterium, Malassezia, Staphylococcus

  • Functions:

    • Maintain scalp health.

    • Prevent dandruff and infections.

🚻 8. Genitourinary Tract

♂ Male:

  • Major Microbes: Lactobacillus, Streptococcus, Corynebacterium

  • Functions: Similar to skin/gut protection, influence reproductive health.

♀ Female:

  • Major Microbes: Lactobacillus (dominant), Gardnerella, Atopobium

  • Functions:

    • Maintain acidic pH (around 4) in the vagina to prevent infections.

    • Influence fertility, pregnancy, and STI resistance.

🧮 TOTAL MICROBIAL LOAD

1. Number of Microbes:

  • Estimated 38–40 trillion microbial cells in the human body.

  • Human cells: ~30 trillion → we are more microbial than human (by cell count).

2. Microbial Genes:

  • Human genome: ~20,000 genes

  • Microbiome: 2–20 million genes → This is our "second genome".

3. Weight:

  • The total microbiome weighs around 1.5–2 kg, mostly concentrated in the gut.

💡 Summary of Roles

Function Description
Digestion Ferment indigestible fibers, absorb nutrients
Immunity Train immune cells, prevent allergies and autoimmunity
Defense Crowd out and kill harmful pathogens
Metabolism Produce vitamins, hormones, SCFAs
Mood & Brain Influence behavior, anxiety, cognition via gut-brain axis