Lecture notes for BIOL121 Impact of Microbes module
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BIOL121: Impact Of Microbes (BIOL121)
Instelling
Lancaster University (LU)
32 page document covering all 12 lectures in the module. Introduces and explains bacteria, viruses, yeasts and protists. Describes the classification system for each one as well as their respective importance (e.g. use in medicine) and diseases caused. Definitions are highlighted throughout.
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Microbiology: study of microbes
Microbes: too small to see clearly be unaided eye
Pathogens: cause infectious disease
Children = most vulnerable as have less developed immune system, LMIC
Bacteria in Food:
+ Cycle carbon + phosphate + Food requires microbial activity
- Food borne disease + Food spoilage
3 Domains:
1. Bacteria:
• Disease causing prokaryotes
• First life forms on earth
• Size depends on nutrient availability
2. Archaea:
• Different molecular organisation to bacteria
• No peptidoglycan in cell wall
• Largely proteinaceous coat
• Ether linked lipids built from peptide chains
• Anaerobes + some obligate anaerobes
• Produce methane
3. Eukaryota:
All organisms except bacteria + blue-green fungi
Cellular properties: compartmentalisation, metabolism, evolution
Some cells: motility, differentiation, communication
Microbial cell sizes:
Viruses 0.01-0.2um
Bacteria 0.2-5um
Yeast 5 – 10um
Eukaryotes 5-100um
Algae 10-100um
Protists 50-1000um
Smaller cells = faster rate of nutrient exchange = faster growth = faster mutation rate = greater
evolutionary possibilities
, Dye washed out -> pink
3. Mycobacterial: thin peptidoglycan, mycolic acid
4. Archaeal: pseudopeptidoglycan, S-layer = proteins + glycoproteins
Gram staining: crystal violet stain -> add iodine -> wash with ethanol -> counter stain with
safranin
Peptidoglycan structure: GM polymer linked via peptide bridges
G (N-Acetylglucosamine) + M (N-Acetylmuramic acid
G + M are alternating
Lysozymes -> break peptide bond -> cell wall loses structure -> kills bacteria
Capsule: made of polysaccharides
➔ Increases size -> protect from phagocytisus
➔ Protects from desiccation
➔ Surface attachment
Fimbriae: short, thin, hair-like appendages
➔ Recognition + surface attachment
Flagella: made of flagellin protein
1. Monotrichous: 1 polar flagellum
2. Amphitrichous: 1 flagellum at each pole
3. Lophotrichous: cluster of flagellum at 1 or both poles
4. Peritrichous: flagella spread out over entire cell surface
Pili: long, thick + less numerous hair-like appendages made of pili protein
➔ Surface attachment
➔ Sex pili: pass genetic material
Bacterial Cytoplasm: gelatinous material = ribosomes, nucleoid, cellular inclusions, macromolecules,
organic molecules, inorganic ions
Nucleoid: irregularly shaped region containing genophore
Plasmid: small circles of DNA + replicate independently of nucleoid
➔ Transfer DNA between species
Cellular inclusions: granules of organic + inorganic material reserved for the future e.g. glycogen,
sulphur + polyphosphate granules
Magnetosomes: store Fe in magnetite form in some pecialist bacteria
➔ Orients cells in magnetic fields
Gas Vesicles: arranged in bundles -> buoyancy e.g. cyanobacteria
Endospores: produced by some gram-ve bacteria -> survival mechanism
Cell differentiates -> spores -> chromosome + other survival apparatus migrates into spore ->
spore attaches to surface + waits for adverse conditions to end
+ Survive long time
+ Stores sulphur
+ Resistance to drying, radiation + chemicals
+ Specialised proteins protect DNA
+ Contain calcium carbonate CaCO3 -> binds to H2O molecules -> dehydrates endospore ->
stabilises DNA
Prokaryote Eukaryote
Cell size < 5um >5um
Number of chromosomes 1-2 >1
, Cell wall Thin + peptidoglycan Thick (plant cells) or absent
Ribosomes in cytoplasm 70S 80S
Ribosomes within organelles No 70S
Cilia No Yes
Flagella Helical arrangement 9:2 Fibril arrangement
Cell division Binary Fission Mitosis
Nutrients: provide all elements involved in cell membrane synthesis
Macroelements: required in large amounts in all cells
C, O, H, N, P -> amino acids, DNA, carbohydrates
S (cysteine, methionine), K (enzyme activity), Ca (cell wall stability), Mg (ribosomes, membrane), Fe
(ET proteins)
Microelements: required in small amounts by some organisms e.g. Cu, Zn, Ni
Bacterial Sampling:
Culture media: nutrient solutions containing all elements required for growth
Chemically defined media: exact chemical composition known
Complex media: digests of complex material – exact chemical composition not known
Batch culture: grown in closed system
Bacterial growth: increase in cell numbers by binary fission
Streaking: produces isolated colonies of bacteria on agar plate
➔ Purification + allows biochemical tests + obtain appropriate colony numbers
Sterilise inoculating loop -> scrape some bacteria off colony -> spread it over agar plate = parallel
lines -> sterilise loop + repeat -> areas of high to low bacterial concentrations
Bacterial Growth:
Binary fission: DNA replication -< cell elongation -> septum formation -> cell separation
Generation time = doubling time
Ideal conditions = constant doubling time = exponential growth
Growth Curve: lag phase -> Log phase -> Stationary phase -> Death phase
VBNC = viable but not culturable -> still cause disease + have low metabolic activity due to stress
Direct microscopic count: uses species microscope counting slide -> count live + dead
1. Total count: stains all bacteria using non-specific dye
2. Viable count: counts active bacteria using fluorescent dye
3. Culturable count: counts cells that form colonies on solid media/ increase turbidity in liquid
media
Culturable count < viable count < direct count
Turbidity: cells scatter light passing through suspension
Antibiotics:
1. Bacteriostatic: stops growth
2. Bactericidal: kills bacteria -> cells still present
3. Bacteriolytic: bursts cells -> releases contents
Nutrient Types:
1. Heterotrophs: organic molecules from other organisms
2. Autotrophs: CO2 carbon source
3. Phototrophs: light -> ATP
4. Chemoorganotrophs: oxidises organic compounds -> ATP
, 5. Chemolithotrophs: oxidises inorganic compounds -> ATP
Oxygen:
1. Obligate aerobes: need O2
2. Obligate anaerobes: O2 = toxic
3. Facultative anaerobes: prefer O2 but don’t need it
4. Aerotolerant anaerobes: O2 has no effect
5. Microaerophilic: need O2 at low concentrations
Temperature:
1. Psychrophiles: 0-20
2. Mesophiles: 20-40
3. Thermophiles: 45-80
4. Hyperthermophiles: >80
pH: acidophiles, neutral zone, alkaliphiles
Osmolarity: solute concentration
1. Mild 1-6%
2. Moderate 7-15%
3. Extreme 15-30% = Halophiles (salt)
Bacterial Disease:
Pathogenicity; ability to cause disease
Virulence: degree of pathogenicity = invasiveness + toxicity = adhesins, invasins, toxins
Infection: bacteria persist in host
Disease: overt damage to host
Primary pathogens: cause disease in absence of immune defects
Opportunistic pathogen: only causes disease when host defences are impaired e.g. Clostridium
difficile (colon infection)
Kochs Postulates:
1. Microorganisms isolated from diseased animal
2. Grown in pure culture
3. Identified under microscope
4. Injected into healthy lab animal
5. Disease reproduces
6. Microorganisms isolated + grown in culture
7. Microorganism identified
Infection Cycle: reservoir -> host -> adherence -> colonisation -> tissue invasion -> tissue damage ->
reservoir/host
1. Reservoir: Pathogens must have 1+ reservoirs
2. Transmission:
a. Direct host-to-host transmission; aerosols, touching kissing
b. Indirect host-to-host transmission: vector borne (living) or vehicle (non-living)
transmission
3. Adherence: stick quickly to host cell surfaces
Streptococci -> adhere to teeth surfaces
Staphylococci -> adhere to shunts + plastic catheters
Non-specific forces -> bacterial adhesins + host receptors acts as anchor -> bacterial aggregation
produces biofilm -> biofilm disperses -> seed new infection sites
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