Microbiology and Resident Flora

Physiological Factors Affecting Survival

• pH levels in different parts of the body affect survival
• Moisture levels play a crucial role in survival
• Temperature and nutrient availability are essential for survival
• Natural inhibitory substances also influence survival

Resident Flora

• Consists of a relatively fixed type of microorganisms regularly found in a given area at a given age
• Members of the normal flora can become pathogenic if:
  • Removed from their environment and introduced into the bloodstream or tissues
  • The balance between microorganisms is lost
  • The host immune system is weakened
• Opportunistic pathogens: members of the normal flora that cause disease when given the opportunity
  • Examples: Staphylococcus aureus, Candida albicans
• Strict pathogens: always associated with disease

Transient Flora

• Consists of microorganisms that inhabit the body surface or mucous membranes for a limited period
• Establish themselves briefly for colonization without disease
• Removed by various factors, and does not reform; a new flora is replenished
• The type of microorganisms in a certain body site depends on the conditions of that body site
• Usually exists together with the permanent flora
• If the permanent flora is removed, transient flora may cause disease
• Most members are non-pathogenic or opportunistic pathogens

Role of Flora in the Organism

• Most microorganisms of the flora are commensals, benefiting from body temperature, moisture, and debris material without harming the human body
• Some microorganisms are mutualistic, helping in:
  • Vitamin synthesis
  • Preventing colonization by pathogenic bacteria via competition

Flora of Outer Environment

• Microorganisms found temporarily or permanently in certain environments:
  • Air
  • Soil
  • Water
• Air is not suitable for the growth and survival of microorganisms
• Microorganisms diffuse into the environment via air flow
• Survival of microorganisms on dust particles or water droplets depends on:
  • Resistance to dryness
  • Existence of organic material
  • Moisture levels
  • Temperature of the environment

Soil Microbial Flora

• Soil is an environment where organic material and water constantly exist
• Numerous microorganisms in the soil play an important role in biotransformation
• Nitrogen, sulfur, and carbon transformation happens via soil microorganisms
• Pathogenic microorganisms transmitted via soil:
  • Clostridia (C. tetani, C. perfringens)

Normal Microflora of the Gastrointestinal Tract

• The human gastrointestinal tract consists of:
  • Stomach
  • Small intestine
  • Large intestine
• Responsible for digestion of food, absorption of nutrients, and production of nutrients by the indigenous microbial flora
• Contains 10^13 to 10^14 microbial cells
• Functions and products of intestinal flora:
  • Vitamins
  • Gas, organic acids, and odor
  • Enzymes

Normal Microflora of Other Body Regions

• Urogenital Tract:
  • The microbiota in urine is less abundant and less diverse than the microbiota in other sites of the body
  • Common genera: Prevotella, Escherichia, Enterococcus, Streptococcus, or Citrobacter
  • Genus Pseudomonas has only been described in men
  • Corynebacterium and Streptococcus, more abundant in women
  • Lactobacillus, more abundant in women

Establishing the Cause of Infectious Disease

• Koch's Postulates:
  1. Asymptomatic carriers: some pathogens can be found in healthy individuals
  2. Non-culturable organisms: some pathogens cannot be cultured in a lab
  3. Ethical concerns: the third postulate may not be ethical to satisfy for certain diseases, especially in humans
  4. Complex diseases: some diseases may have multiple contributing factors, including more than one causative agent
  5. Molecular Koch's Postulates: a set of postulates to establish causality at the genetic and molecular levels
  6. Viral diseases: Koch's Postulates were formulated before the discovery of viruses, which cannot be cultured in the same way as bacteria

Normal Flora of the Human Body

• Normal flora is defined as populations of microorganisms routinely found growing on the body of healthy individuals
• Microorganisms choose a body site suitable for their growth and survive there