Microbial Ecology and Symbiosis

Microbial Ecology

• Study of the interrelationships between living organisms and their environment
• Two components:
  • Biotic (living): plants, animals, and other organisms
  • Abiotic (non-living): water, soil, and atmosphere

Symbiosis

• Interaction between two dissimilar organisms (symbionts)
• Types:
  • Neutralism: neither symbiont is affected
  • Commensalism: beneficial to one symbiont, no consequence to the other
  • Mutualism: beneficial to both symbionts

Examples of Symbiotic Relationships

• Indigenous microflora in humans: no consequence to either

• Demodex folliculorum: mites in human hair follicles, rarely harmful

• Dermatobia hominis: human bot fly; eggs laid on vectors, larvae develop under skin

• Humans and intestinal normal microflora: mutualistic relationship; microorganisms provide vitamins, like Vitamin K produced by E. coli

Medicinal Leeches

• Used historically for abscesses and wounds
• Contain Aeromonas spp., essential for blood digestion, which benefits the host
• Use may lead to wound infections by Aeromonas spp., therefore prophylactic antibiotics should be used

Wolbachia

• Intracellular bacteria related to Rickettsia
• Obligate intracellular parasite; infects ovaries and testes only
• Essential for survival and embryogenesis of some species (e.g., filarial nematodes)
• Sterile insect technique (SIT) for controlling mosquitoes

Termites

• Insects that cannot digest wood
• Intestines contain protozoa aiding in wood digestion

Lichen

• Patches on tree trunks and rocks
• Composed of fungi (hyphal cells) and algae (photosynthesis).

Parasitism

• One organism benefits (parasite) and another is harmed (host)
• May be pathogenic causing disease, or non-pathogenic.

Human Indigenous Microflora

• Microorganisms naturally inhabiting human body, with no harm
• Resident microbiota: always present
• Transient microbiota: temporarily residing

Microflora of Skin, Ears, and Eyes

• Skin: primarily anaerobes, with bacteria like Staphylococcus epidermis and Corynebacterium spp.
• Ears: similar to skin microflora in the outer ear
• Eyes: Staphylococcus, Streptococcus, and Corynebacterium species

Microflora of Respiratory Tract

• Upper respiratory tract: harmless or opportunistic microbes (e.g., Staphylococcus, Streptococcus)
• Lower respiratory tract: usually sterile

Microflora of Mouth

• Primarily anaerobic bacteria, with species like Streptococcus and Porphyromonas associated with periodontal disease

Microflora of GIT

• Stomach: acidic environment, minimal flora except Helicobacter pylori
• Small intestine: bile inhibits most microorganisms
• Colon: large variety of microorganisms

Microflora of Urinary Tract (UGT)

• Kidneys, ureters, and bladder are generally sterile
• Urethra may harbor bacteria, such as those causing urinary tract infections (UTIs)

Beneficial Role of Microflora

• Production of vitamins (e.g., Vitamin K)
• Constant stimulation of the immune system (immune response)
• Antibacterial mechanisms (bacteriocins)

Probiotics (Biotherapeutic MOs)

• Harmless microorganisms that provide health benefits
• Ingested in fermented foods (e.g., yogurt)
• Improve gut health, increase microbial diversity, potentially replacing pathogenic microorganisms

Harmful Role of Microflora

• Opportunistic pathogen behavior: change habitat or weaken immune response
• Potential for disease such as infections of urinary bladder, blood stream, lungs, or wounds

Biofilm

• Complex microbial community embedded in a polymeric substance.
• Resistant to antibiotics and disinfectants due to factors like their layers and hydrophobicity.

Synergism

• Two or more different microorganisms interact to produce a disease or effect a host that neither could cause individually.
• Examples include acute necrotizing ulcerative gingivitis (ANUG) and bacterial vaginosis

Probiotics (Biotherapeutic MOs)

• Harmless microorganisms that provide health benefits.
• Ingested in fermented foods (e.g., yogurt)
• Improve gut health by increasing microbial diversity and potentially replacing pathogenic microorganisms
• Other ways to use probiotics include nasal spray or fecal microbiota transplantation

Harmful Role of Microflora

• Potential for disease: change habitat, weaken immune response, or cause infections in different parts of the body