Normal Microbiota Handout 2

Description: Most animals and plants have a continuous population of microorganisms present on their outer surfaces and inside specific bodily cavities.
Types of Microorganisms: Includes bacteria, fungi, and viruses.
Ubiquitous Nature: Microorganisms are found throughout various environments, which is described by the term "ubiquitous."
Microbial Competition:
- Continuous competition occurs among microorganisms for nutrients and physical space.
- Producing materials that inhibit or kill other microorganisms can be viewed as a form of chemical warfare.
- Example: The development of antibiotics by one species leads to counter-measures by others.
- Result: Under typical conditions, microbial populations reach a state of equilibrium, where their numbers are kept low.

Commensalism:
- Microorganism benefits from living in or on the host.
- The host is neither significantly benefitted nor harmed.
Mutualism:
- Both the host and the microorganism benefit from their interaction.
Parasitism:
- Only the microorganism benefits, usually causing some degree of harm to the host.

Structure: The skin consists of an outer layer of dead, flattened, and highly keratinized squamous epithelium.
- Characteristics: Relatively waterproof, gas proof, and impermeable to most microorganisms.
pH Regulation:
- Secretions of fatty acids via skin pores and the presence of certain bacteria (e.g., Staphylococcus spp.) lower skin pH, making it acidic and inhibiting growth of many organisms.
Sweat Glands:
- Produce sebum—rich in fatty acids, salts, and proteins—serving as nutrients for microorganisms.
- Accumulation can block sweat glands, forming comedones (sebum plugs).
Moisture Levels:
- Areas like the scalp, underarms, and groin have higher microbial diversity due to increased moisture.
Lysozyme:
- An antibiotic found primarily in saliva and tears that can inhibit and kill gram-negative bacteria, protecting the cornea from infection.

Propionobacterium acnes:
- Lives within hair follicles and sweat glands. Increased sebum production can lead to acne during hormonal changes (puberty, pregnancy).
Staphylococcus spp.:
- Includes S. aureus and S. epidermidis, prevalent on skin and especially in and around nostrils and nasal cavity.
Fungi:
- Require higher moisture, found in conditions like athlete's foot and dandruff (dermatitis).

Microorganisms: Includes Lactobacillus acidophilus and Streptococcus mutans.
Impact of Lactobacillus:
- Can lower the pH of the mouth to a level that dissolves tooth enamel, leading to dental caries (tooth decay).

Lower Respiratory Tract:
- Generally, not colonized by microorganisms.
- Epithelium has goblet cells (mucus production) and ciliated cells (mucus movement).
- System: Muco-Ciliary Escalator prevents inhaled microorganisms from settling.
Alveoli:
- Lack goblet or ciliated cells. If organisms colonize here, it may lead to infections like pneumonia.

Microorganisms:
- Includes Streptococcus pneumoniae and Haemophilus influenzae.
- Normally kept at low levels by microbial competition and a healthy immune system.

Colonization:
- Normally not colonized due to low pH (around 2-3).
- Exception: Certain organisms like Helicobacter pylori can survive and are associated with ulcers and chronic gastritis.

pH Changes:
- pH shifts from acidic (stomach) to more basic (intestines) due to bile salts and digestive enzymes.
Diversity of Microbiota:
- A wide variety of microorganisms prosper in the intestinal tract, contributing to vitamin production.
- Enterics: Organisms residing in the intestinal tract.
- Largest family: Enterobacteriaceae. Note that all members of Enterobacteriaceae are enterics but not all enterics belong to Enterobacteriaceae.

Urinary Tract:
- Typically sterile except for the distal parts of the urethra where microorganisms can be found.
- Freshly produced urine is acidic and sterile.
Vaginal Microbiota:
- Lactobacillus acidophilus colonizes the vagina, lowering pH to inhibit growth of unwanted organisms.

Sterile Environment:
- Uterine environment is normally sterile. Microorganisms first colonize infants during birth and shortly after.
- Notably, this is the only time in life that a person is free from microbial colonization.

Microbial competition regulates the population levels of various microorganisms, maintaining equilibrium.
Disruption in normal microbiotic populations can favor the growth of potentially harmful organisms, leading to diseases like thrush due to fungal overgrowth.

Importance of Soil Microorganisms:
- Critical in organic/inorganic decomposition for environmental stability.
- Examples:
- Rhizobium and Azotobacter fix atmospheric nitrogen for plants.
Bio-remediation:
- A process that manipulates microorganisms to cleanse and restore polluted environments.

The need for balanced and stable microbiotic populations is essential for:
- Control over growth and spread of harmful organisms.
- Performance of critical biological functions, including nutritional support and immune system stimulation.
- The notion that sterilizing the body would be detrimental due to the roles of beneficial microorganisms.