Friendly Bacteria Living with Us

 

2.8 – Normal Flora (Harmless Microbes Living in Our Body)

Definition

• In a healthy animal, internal tissues (blood, brain, muscle, etc.) are normally microbe-free (sterile).
• Surface tissues (skin, mucous membranes) are in constant contact with the environment → colonized (inhabited) by specific microbes.
• The mixture of organisms regularly found at any body site = Normal Flora.

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Composition of Human Normal Flora

• Mostly bacteria (most numerous).
• Few fungi.
• Some protists (unicellular eukaryotes).
• Some methanogenic archaea (microbes producing methane gas).

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Benefits of Normal Flora (Mutualism – both benefit)

1. Synthesis of Vitamins

   • Normal flora in alimentary canal produce vitamins.

   • Extra vitamins secreted → absorbed in body.

   • Examples:

     • Enteric bacteria (gut bacteria) → Vitamin K, Vitamin B12.

     • Lactic acid bacteria → Certain B-vitamins.

2. Prevent Colonization by Pathogens

   • Normal flora compete (fight for space & food) with harmful microbes.

   • Pathogens find it hard to attach or invade tissues.

3. Inhibit or Kill Pathogens

   • Intestinal bacteria secrete substances (toxins/chemicals) → inhibit or kill harmful bacteria.

4. Stimulate Immune System

   • Normal flora act as antigens (foreign substances) → body makes low-level antibodies.

   • These antibodies cross-react (also attack similar pathogens) → protect body from infections.

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✅ Exam Tip:

• Remember 4 main benefits: Vitamins, Competition, Killing pathogens, Immunity.

• One-line definition: Normal flora = harmless microbes naturally living on skin & mucous membranes that protect and benefit the host.