microbe symbiosis

• Normal biota


  The many microorganisms that inhabit the surfaces of our bodies
• Types of biotas

  • Resident
  • Transient
  • Opportunistic
• Resident biota


  The microorganisms that inhabit the human body throughout life
• The microbial species and sizes of their populations may change, but the resident biota is permanent
• Transient biota


  Those microorganisms that come to rest on our body surfaces
• Frequent hand washing is important in removing transient biota in hospital workers
• Opportunists


  Microorganisms able to cause disease under three main circumstances: a weakened immune system, broad-spectrum antibiotics have been administered which altered microbial flora and medical devices have been implanted
• Symbiosis


  The many interactions between microorganisms, which may be positive or negative
• Types of symbiosis

  • Ectosymbiont-one organism is located on the surface of another

  
  

  • Endosymbiont-one organism is located within another.
• Commensalism


  One partner benefits and the other partner neither benefits nor is harmed
• Microbial Antagonism


  Normal biota collectively out competes pathogens and prevents them from establishing disease
• Mutualism


  Both partners benefit
• Parasitism

  One partner (host) is harmed and the other partner (parasite) benefits
• 'Parasites' is a term generally reserved for the protozoa, worms & helminths
• Factors that determine Normal Biota

  • Human factors
  • Microbial factors
• Human factors


  Living tissues or surfaces can present Structural, Mechanical or Biochemical barriers to microbial growth
• Human factors barriers are called non-specific surface defenses because they act against most or all microorganisms
• Structural defenses


  Epithelial surfaces, which are composed of cells that are tightly packed together to form a seamless, relatively impermeable barrier to microbes
• Structural defenses function to provide a barrier to microbes and as the epithelium grows, it sloughs off cells that are replaced by new ones, controlling the population size of microbes
• Epithelial surfaces

  • Skin-covers the exterior of the body, excluding the eye.

  
  

  • Mucous membrane-covers the surface of the eye and all of the body’s interior surfaces.
• Mechanical defenses


  Movements of tissues and body fluids that remove microbes
• Types of mechanical defenses

  • Movements along body surfaces that remove microbes
  • Movements in the mucociliary system that move mucus and trapped microbes
  • Movement of body fluids that dislodge microbes
• Biochemical defenses


  The use of chemicals against microbes, such as acidifying body surfaces and producing enzymes
• Microbial factors


  Adaptations that allow some species of microorganisms to thrive on body surfaces despite body defenses, such as the ability to take iron from human proteins, adhere to human cells, and produce bacteriocins
• Mechanical Movements

  1. Occur along body surfaces

  2. Remove microbes that happen to land there

  3. Eg. Peristaltic movements that move food and waste through the upper portion of the digestive tract often act to dislodge microbes
• Mechanical Movements in the mucociliary system


  1. Brought about by the action of cilia on epithelial cells

  2. Move mucus (and trapped microbes) along towards the mouth

  3. Where it is swallowed and eventually eliminated
• Mechanical Movement of body fluids

  1. Bathe some surfaces

  2. Dislodge microbes

  3. Eg. Rapid flow of urine that flushes the urethra, tears that continually bathe the conjunctivae
• Adaptation


  • Ability to take iron that is bound to human proteins
  • Use siderophores (iron chelators) to strip the protein from the iron
• Ability to adhere to human cells

  • Species that are part of the human biota attach themselves to epithelial cells using adhesins
  • Adhesins are proteins found on bacterial cell surfaces that allow the bacterium to adhere to a substrate
• Adhesins


  Specific proteins that bind only to specific receptors on host cells
• Ability to produce bacteriocins

  • Bacteriocins are toxic compounds that kill or inhibit bacterial competitors that compete for space or nutrients