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41 Cards in this Set
- Front
- Back
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Briefly describe microbial metabolism in two points.
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> Bacteria have many of the same pathways for synthesis of compounds (such as proteins) and for energy generation as do eukaryotes
> They have a greater diversity of pathways, consistent with their various habitats |
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Describe the mode of transport of substrates
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Substrates from the environment are transported into the bacterial cell via passive diffusion, facilitated diffusion and by active transport
Enzyme systems determine which substrates can be utilized |
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What are the extracellular enzymes released by the bacterium? Why is it significant?
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Proteins are actively secreted by a variety of different types of secretory systems
This includes secretion of enzymes such as proteases, nucleases, phospholipases etc, some of which can can cause important tissue damage, as well as specific toxins |
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What metabolic pathways does the bacterium utilises?
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Most utilises the glycolytic pathway from glucose to pyruvate for energy generation.
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Name 3 practical aspects about bacterial metabolism.
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Knowledge of bacterial metabolism allows one to make growth media that favour the metabolism and growth of a particular species (see later)
Can add a substrate that is used by one species, but not by an otherwise similar species: if it can grow, this helps to identify the species in question Can look at the end products of growth on a defined medium: eg six different patterns of anaerobic metabolism of pyruvate (eg E. coli produces mixed acid and gas from pyruvate) |
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Regulation of enzyme metabolism is via enzyme systems. What are the two called?
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1. Regulation of enzyme activity.
2. Regulation of enzyme production. |
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Negative feedback loops on pathways :........... ............
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Rapid control
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Regulation of enzyme production is slower with two ways to control it , repression and induction.Describe both.
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Repression: the end product activates a repressor which then shuts down the transcription of the enzyme operon
- Induction: a substrate inactivates a repressor that otherwise blocks transcription of a pathway (eg lac operon, making lactase) |
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individual cells > growth , name two methods
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Mainly:
i) Binary fission into 2 equal cells Occasionally: ii) Asymmetrical “budding” e.g. yeasts: small progeny then grows to full size |
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Deacribe replication
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Circular chromosome
Replication bi-directional away from “point of origin” Semi-conservative: both strands copied, 5’ to 3’ 800 bases/second Chromosome is membrane associated New chromosomes separated by membrane growth |
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One plane of divisions leads to what form of bacteria? GIve an example.
3 plane division leads to ...? Give an bacteria eg. |
Streptococcus always end up forming chains.
Staphylococcus forms bunches form grapes. |
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In a population growth curve what does the lag phase refer to?
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Cells increasing in size and metabolic activity “Adjusting”
New environmental conditions (substrate) Old depleted cells >Reduce lag phase by inoculating large numbers of young dividing cells to the same medium |
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What happens in the exponential phase?
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Rapid division (doubling): fastest under optimal environmental conditions
All young cells: usually most infective at this stage |
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What happens in the stationary phase?
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Decreasing growth rates, smaller cells
Depletion of nutrients and build up of toxic products Cell death = cell division |
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What happens in the decline phase?
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>> Decline phase
Death rate exceeds division = End phase in “Batch culture” |
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What does the total cell count refer to?
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Total count of both viable and dead cells.
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What does direct count refer to?
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Use a counting chamber and count every cell in a known volume= total live and dead.
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Viable count : Colony count , name 3 methods
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1)Miles and Misra
2) Pour plate technique 3) Filtration technique |
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Miles and Misra technique , describe it
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Make serial dilution of bacterial culture
- Then drop out known volumes from each dilution onto plates and incubate: Optimal ~ 30 to 300 colonies/plate |
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Pour plate technique (3)
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Bacterial dilutions suspended in molten (42OC) agar
Pour the agar into plates Incubate and count the colonies that grow |
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What is the filtration technique used for?
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useful where there are small numbers of bacteria in a large volume of water or other fluid. Bacteria trapped on a filter, then the filter incubated on a plate. Individual bacteria on the filter grow up into colonies
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How does electrical resistance method count?
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Bacteria in liquid mrdium pased though a narrow hole and changes in electrical resistance across the hole are equated to the passing of individual cells.
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Mention 3 ways to describe the 3 ways to describe microbial mass.
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->Cell densities in solution
- compare with opacity standards eg “Brown’s tubes” or “Macfarland’s standards” > Wet weights >Dry weights |
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How can we calculate microbe numbers via nitrogen?
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From nitrogen content we can estimate the amount of protein and hence bacterial numbers.
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Why does growth of microbes reach a plateu when provide with excess nutriets?
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Growth then cannot increase further because transport mechanisms are saturated
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3 points about temperature on microbial growth (3 types of bacteria)
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1.Thermophiles like it hot (archaea)
2.Mesophiles include most pathogens (optimum ~ 37oC) 3. Psychrophiles grow at low temperatures (eg Listeria, Yersinia and meat spoilage organisms like Pseudomonas) |
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Describe the effect of salt, osmotic pressure on bacteria.
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Most bacteria do not handle high osmotic conc well. Staph aureus will grow well in the presence of high salt conc and this can be used to help isolate the bacteria on the agar plate.
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What are the 5 classes of bacteria (gaseous environment)?
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1. Obligate aerobes.
2. Facultative anaerobes 3. Aerotolerant anaerobes 4. Microaerophiles 5. Obligate anaerobes |
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Describe and give an example of Obligate (strict) aerobes.
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e.g. Pseudomonas sp., Mycobacterium tuberculosis
Little or no fermentation - lack enzyme systems |
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Describe and give an example of Facultative anaerobes
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Facultative anaerobes
e.g. Enterobacteriaceae Can grow without air, but shift to aerobic respiration in presence of air |
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Describe and give an example of Aerotolerant anaerobes.
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Aerotolerant anaerobes
- anaerobes which survive in air but don’t shift to aerobic respiration |
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Describe and give an example of Microaerophilic.
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Microaerophilic
e.g. Brucella sp. - prefer reduced oxygen tensions (and extra CO2) |
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Describe and give an example of Obligate (strict) anaroebes.
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Obligate (strict) anaroebes
e.g. Clostridia sp - cannot tolerate oxygen - lack superoxide dismutase so cannot break down superoxide (O²) produced by flavoproteins. Also lack catalase. |
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What do you need to supply in a culture medium?
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Need to supply:
- energy - carbon source - nitrogen source - inorganic radicles e.g. Na, + Fe ++, Ca ++ - some require accessory growth factors e.g. vitamins |
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What is the pH of the culture medium?
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pH usually slightly alkaline (7.2 – 7.4), although should be slightly acidic for fungal media
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Describe the basal media.
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- contain meat extracts
- support most micro-organisms e.g. nutrient agar/broth |
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Describe the enriched media.
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- basal media + supplements
e.g. blood, serum |
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What is solid media?
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- used for isolation of single cells: these cells grow into discrete colonies
- potatoes - gelatin (Robert Koch) - agar (long chain polysaccharide): often add growth factors etc to the agar to make an “enriched medium” |
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What is liquid media?
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LIQUID MEDIA - used for subsequent growth of pure cultures
- eg Peptone water = meat digest + salt + water: pH 7.2 - Nutrient broth (“Lab lemco”) = Peptone water + meat extracts, minerals etc |
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What would you use to enhance growth?
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To enhance the isolation/growth of specific bacterial species you can use selective media (agar) and/or enrichment media (broth)
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Describe the enrichment media of broths
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contain factors that favour growth of a desired organism (without necessarily harming others)
e.g. Selenite broth for Salmonella “Mycobactin” an extract that enhances the growth of Mycobacterium paratuberculosis |
