Microbial System

Acknowledgment of Country

  • The University of Notre Dame begins all academic activities by paying respect to the Traditional Owners and Custodians of the lands on which its campuses are situated.
    • Fremantle Campus → Walyalup Country (Whadjuk Noongar people).
    • Broome Campus → Yawuru Country.
    • Sydney Campus → Gadigal Country (Eora Nation).
  • Emphasises continual cultural respect and recognition of Aboriginal and Torres Strait Islander peoples.

Learning Objectives (Session “Microorganisms & Human Health”)

  • Define microorganisms.
  • Distinguish prokaryotes from eukaryotes.
  • Describe major microorganism groups: bacteria, archaea, algae, fungi, viruses, protozoa, helminths.
  • Explain key ecological terms: pathogen, microbiome, symbiosis, mutualism, commensalism, parasitism, opportunism.
  • Discuss microbiota, biofilm formation, and the roles of pre-, pro-, and post-biotics.
  • Outline nursing / public-health considerations and basic prevention.
  • A short quiz follows the lecture to consolidate knowledge.

What Are Microorganisms?

  • Prefix “micro-” = small; organisms invisible to the naked eye — require microscopy.
  • Two broad categories:
    • Cellular (have cells):
    • Bacteria, algae, fungi, protozoa, helminths ("worms").
    • Acellular (non-cellular infectious agents):
    • Viruses, viroids (plant pathogens; not studied further in this course).

Prokaryotes vs Eukaryotes

  • Prokaryotes
    • Lack membrane-bound nucleus and most organelles.
    • Generally small, simple, unicellular.
    • DNA is circular, located in nucleoid region.
    • Include bacteria and archaea.
  • Eukaryotes
    • Possess true nucleus and membrane-bound organelles (ER, mitochondria, etc.).
    • Contain cytoskeleton; may be unicellular or multicellular.
    • Some exhibit motility via cilia/flagella.
  • Shared Structures (across both domains)
    • Ribosomes, DNA, cytoplasm, plasma membrane, and (in some) flagella.

Bacteria

  • Prokaryotic, unicellular; reproduce asexually (binary fission).
  • Cell envelope
    • Some species lack a cell wall; others possess peptidoglycan-rich walls.
  • Habitats: extreme (hot springs, salt lakes) to commonplace, moisture-rich surfaces.
  • Pathogenic examples
    • Skin: Staphylococcus aureus → boils, cellulitis.
    • Respiratory: Streptococcus pneumoniae → pneumonia, otitis media.
    • GI / UT: Escherichia coli → gastroenteritis, UTIs.
  • Beneficial example
    • Lactobacillus spp. in gut aid carbohydrate fermentation & digestion.
  • Treatment: sensitive to antibiotics (depends on resistance profile).

Archaea vs Bacteria (Key Contrasts)

  • Both prokaryotic, yet differ structurally & physiologically:
    • Cell-wall composition
    • Archaea: NO peptidoglycan.
    • Bacteria: peptidoglycan present.
    • Antibiotic sensitivity
    • Archaea: generally resistant.
    • Bacteria: usually sensitive (exceptions = resistant strains).
    • Genomic organisation
    • Archaea: DNA associated with histones.
    • Bacteria: histones absent.
    • Pathogenicity
    • Archaea: no confirmed human diseases.
    • Bacteria: wide spectrum of pathogenic & mutualistic roles.

Viruses

  • Acellular particles composed of nucleic acid (DNA or RNA) enclosed in a protein capsid; some possess lipid envelope.
  • Obligate intracellular parasites — biologically inert outside host cells → debated “living” status.
  • Lack ribosomes & metabolic enzymes; hijack host machinery to replicate.
  • Unaffected by antibiotics; managed by antivirals or vaccines.
  • Examples
    • Herpes simplex virus (HSV-1/2).
    • SARS-CoV-2 (COVID-19 agent).

Helminths (Parasitic Worms)

  • Multicellular eukaryotes, parasitic lifestyle.
  • Transmission routes
    • Fecal-oral ingestion of ova/larvae.
    • Transdermal penetration (e.g.
      walking barefoot on contaminated soil).
    • Insect vectors (flies, mosquitoes).
    • Poor hygiene / sanitation.
  • Prevention & management
    • Anti-helminthic drugs.
    • Health education: regular hand-washing, proper footwear, improved toilets.

Fungi

  • Eukaryotic; cell walls contain chitin.
  • Morphological forms
    • Moulds: multicellular filaments (hyphae → mycelium).
    • Yeasts: unicellular (e.g.
      Candida albicans).
  • Spread by direct skin contact or fomites (clothing, surfaces).
  • Diseases / examples
    • Ringworm (tinea corporis).
    • Vaginal candidiasis.
  • Treatment: antifungal medications (topical or systemic).

Ecological & Clinical Terminology

  • Pathogen: any microorganism capable of causing disease.
  • Microbiota: the full collection of microorganisms inhabiting a particular site (e.g.
    gut, skin).
  • Microbiome: the combined genetic material & interactive network of those microorganisms within the host.
  • Symbiosis (general): two organisms living in close association.
    • Example: Bacillus spp. in gut releasing anti-inflammatory mediators.
  • Mutualism: both partners benefit.
    • Example: certain E. coli strains synthesize Vitamin K\text{Vitamin K} for the host; host provides nutrients & habitat.
  • Commensalism: one benefits, other unaffected.
    • Example: Staphylococcus epidermidis consumes dead skin cells without harming host.
  • Parasitism: one benefits at the host’s expense.
    • Example: ticks & fleas feeding on human blood.
  • Opportunistic pathogens
    • Normally harmless but cause disease when displaced or immunity drops.

Resident vs Transient Microorganisms

  • Resident (Normal) Flora
    • Permanently colonise specific body sites; recolonise after disturbance.
    • Example: S. epidermidis on skin.
  • Transient Flora
    • Temporarily present; can be pathogenic or harmless; usually removed by host defences or hygiene.
    • Example: S. aureus on healthcare workers’ hands.

Microbiota: Functions & Locations

  • Core functions
    • Digest complex polysaccharides → short-chain fatty acids (energy).
    • Generate ATP\text{ATP} and vitamins (e.g.
      K, B-group).
    • Educate & modulate immune system (tolerance vs inflammation).
    • Produce hormones, neurotransmitters (serotonin), and gases (H₂, CH₄).
  • Major anatomical niches
    • Oral cavity.
    • Small & large intestine.
    • Skin (moist & dry sites).
    • Vagina.
    • Upper respiratory tract.

Factors Influencing Optimal Microbiota

  • Balanced diet rich in fibre, fruits, vegetables.
  • Adequate sleep and physical activity.
  • Antibiotic exposure → dysbiosis (loss of resident populations) if indiscriminate.

Biofilms

  • Definition: structured community of microorganisms attached to a surface and embedded within a self-produced extracellular polymeric substance (EPS) “slime”.
  • Everyday example: dental plaque on teeth.
  • Clinical significance
    • Implicated in 60%−80%60\% - 80\% of persistent infections, esp. on medical devices (catheters, prosthetics) and chronic wounds.
    • Catheter-Associated Urinary Tract Infection (CAUTI).
    • Non-healing pressure ulcers.
  • Management
    • Mechanical removal: debridement, brushing, flossing.
    • Antimicrobials: targeted antibiotics/antiseptics; silver-impregnated dressings if no allergy.

Pre-, Pro-, and Post-Biotics

  • Prebiotics
    • Non-digestible food components that selectively nourish beneficial gut microbes.
    • Typically complex carbohydrates / dietary fibre → found in fresh fruits & vegetables.
  • Probiotics
    • Live microorganisms which, when administered in adequate amounts, confer a health benefit to the host.
    • Must survive gastric acidity, colonise, and produce helpful metabolites.
  • Postbiotics (briefly mentioned)
    • Bioactive compounds generated by probiotic metabolism (e.g.
      short-chain fatty acids); confer benefits even without live organisms.

Nursing & Public-Health Considerations

  • Hand hygiene to control transient flora & prevent opportunistic infection.
  • Judicious antibiotic use to avoid microbiota disruption & resistance.
  • Patient education on diet (prebiotic intake) and appropriate probiotic supplementation.
  • Correct catheter care and wound management protocols to minimise biofilm formation (e.g.
    routine dressing changes, aseptic technique).
  • Monitoring for signs of fungal or helminthic infections in at-risk populations; administer antifungals/anti-helminthics as ordered.

Next Steps

  • Complete the end-of-session quiz to reinforce terminology, distinctions between microorganism groups, and clinical applications.
  • Review these notes alongside textbook diagrams for visual reinforcement.