Microbiology Study Notes: Prokaryotes, Eukaryotes, and Pathogenic Microorganisms

Prokaryotes: Bacteria – Complex Life Cycles

The Tree of Life – Evolution of Life on Earth

• Genetic Relationships: Determined by analyzing conserved genes across organisms.

• Ancestry Determination: Based on 16S rRNA gene sequence comparison.

• Carl Woese's Contribution: Established the three-domain system (Bacteria, Archaea, Eukarya).

Bacterial Cell Properties

• Cell Wall: Composed of peptidoglycan; distinguishes Gram-positive from Gram-negative bacteria.

• Cell Shapes: Cocci (spheres), bacilli (rods), spirilla/spirochetes (spiral), coccobacilli, vibrio (comma-shaped).

• Cell Growth and Metabolism: Growth curves describe bacterial population changes over time.

Complex Life Cycles of Bacteria

• Biofilms: Communities of bacteria attached to surfaces, encased in extracellular polymeric substances. Visualized by FM, crystal violet, or filtration.

• Sporulation: Formation of endospores (e.g., Bacillus, Clostridium), visualized by LM or Schaeffer-Fulton stain.

Prokaryotes: Bacteria – Motility & Chemotaxis, Adherence & Colonization

Bacterial Cell Properties and Behaviors

• Motility: Movement via flagella (protein filaments), pili, or actin-based motility (e.g., Listeria).

• Chemotaxis: Movement in response to chemical gradients.

• Adhesion/Attachment: Pili/fimbriae, afimbrial adhesins, and biofilm formation. Examples: Staphylococcus, Streptococcus, Caulobacter.

• Colonization: Two-step process: attachment and establishment (e.g., E. coli).

Prokaryotes: Bacterial Pathogens – Extracellular & Intracellular Pathogens

Extracellular vs. Intracellular Pathogens

• Extracellular Examples: Propionibacterium acnes, Staphylococcus aureus, Pseudomonas aeruginosa, Vibrio cholerae, Haemophilus influenzae.

• Intracellular Examples: Listeria monocytogenes, Brucella abortus, Salmonella enterica, Mycobacterium tuberculosis, Chlamydia, Coxiella.

Survival in the Host

• Invasion and Dissemination: Use of spreading factors (nucleases, proteases, hyaluronidases, etc.).

• Nutrient Acquisition: Siderophores for iron uptake, glycosidases for sugar acquisition.

• Immune Evasion: Capsules, antigenic variation, inhibition of phagocytosis.

• Invasion of Host Barriers: Phagosome escape (e.g., Listeria), survival in macrophages (Mycobacterium tuberculosis).

Bacterial Toxins

Types and Effects

• Small Molecule Toxins: Endotoxins (LPS), pertussis toxin, diphtheria toxin, etc.

• Large Protein Toxins: Exotoxins (hemolysins, enterotoxins, AB toxins).

• AB Toxins: Two-component toxins (e.g., diphtheria toxin, cholera toxin).

• Toxin Delivery: Type 1–7 secretion systems (e.g., Type 3 and Type 6 in Salmonella).

Prokaryotes: Archaea

Archaeal Properties and Evolution

• 16S rRNA: Used for phylogenetic classification; Archaea are a distinct domain.

• Main Phyla: Euryarchaeota (methanogens, halophiles), Crenarchaeota (thermophiles).

• Cell Structure: S-layer, ether-linked membrane lipids, lack of peptidoglycan.

• Metabolism: Methanogenesis (production of methane from CO2 and H2).

Eukaryotes: Algae, Fungi

Algae

• Photosynthetic Eukaryotes: Major source of O2 in the atmosphere.

• Types: Chlorophyta (green algae), Rhodophyta (red algae), Phaeophyta (brown algae), diatoms, dinoflagellates.

• Applications: Food, agar, carrageenan, biofuels, pollution control.

Fungi

• Structure: Unicellular (yeasts) or multicellular (molds, mushrooms).

• Roles: Decomposition, nutrient cycling, symbiosis, food production, antibiotics (e.g., penicillin).

• Fungal Cell Wall: Composed of chitin, glucan, and other polysaccharides.

Eukaryotes: Fungal Pathogens

Pathogenic Fungi

• Ascomycetes: Includes molds (Penicillium, Aspergillus) and yeasts (Candida, Histoplasma).

• Basidiomycetes: Includes mushrooms and yeasts (Cryptococcus neoformans).

• Pathogenic Mechanisms: Allergens, toxins, invasive growth, opportunistic infections.

Eukaryotes: Parasites (Protozoans)

Characteristics of Protozoan Parasites

• Life Stages: Trophozoite (active), cyst (dormant, environmental resistance).

• Motility: Cilia, flagella, pseudopodia.

• Transmission: Fecal-oral, vector-borne, direct contact.

Examples of Protozoan Pathogens

• Amoebas: Entamoeba histolytica (dysentery), Acanthamoeba (encephalitis).

• Flagellates: Giardia intestinalis (diarrhea), Trichomonas vaginalis (STD), Trypanosoma (sleeping sickness, Chagas disease), Leishmania (leishmaniasis).

• Apicomplexans: Plasmodium (malaria), Cryptosporidium parvum (diarrhea).

Table: Comparison of Major Microbial Groups

Group	Cell Type	Cell Wall	Motility	Reproduction	Examples
Bacteria	Prokaryotic	Peptidoglycan	Flagella, pili	Binary fission	E. coli, Staphylococcus
Archaea	Prokaryotic	Pseudopeptidoglycan or S-layer	Flagella (distinct from bacteria)	Binary fission	Methanogens, halophiles
Fungi	Eukaryotic	Chitin, glucan	Non-motile (except some spores)	Spores, budding	Aspergillus, Candida
Algae	Eukaryotic	Cellulose, silica	Flagella (some)	Sexual/asexual	Chlamydomonas, diatoms
Protozoa	Eukaryotic	None	Cilia, flagella, pseudopodia	Binary fission, sexual	Plasmodium, Giardia

Key Equations

• Bacterial Growth:

$N_t = N_0 \times 2^n$

• Where $N_t$ = number of cells at time t, $N_0$ = initial number of cells, $n$ = number of generations.

• Generation Time:

$g = \frac{t}{n}$

• Where $g$ = generation time, $t$ = total time, $n$ = number of generations.

Additional info: These notes synthesize and expand upon the provided lecture outlines, adding definitions, examples, and context for clarity and completeness.