Microbiology Chapter 5.txt

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Microbiology Chapter 5.txt
2010-06-17 12:53:28
Microbiology Five

Microbiology Five
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  1. Bacteria reproduce by
    • Binary fission
    • The cell doubles in mass
    • DNA replicates and the two strands separate
    • The cell wall and cell membrane begin to invaginate
    • A cross wall forms
    • The cell separates
  2. Cytokinesis
    Is an inward pinching of the cell membrane and cell wall to separate the cell into two genetically identical cells
  3. Doubling Time
    • The generation (or doubling) time is the interval of time between successive binary fissions
    • In pathogens, a shorter doubling time means a shorter incubation period of disease
  4. Growth Curve
    • Lag phase - Getting used to new environment
    • Log phase - Exponential growth
    • Stationary phase - Birth rate = death rate
    • Death phase - Waste (typically acid) contaminates the environment and causes death
  5. A Bacterial Growth Curve Illustrates the Dynamics of Growth
    • During the lag phase, no cell division occurs while bacteria adapt to their new environment
    • When reproductive and death rates equalize, the population enters the stationary phase
    • The accumulation of waste products and scarcity of resources causes the population to enter the decline (exponential death) phase
    • Exponential growth of the population occurs during the logarithmic (log) phase
    • Human disease symptoms usually develop during the log phase
    • When reproductive and death rates equalize, the population enters the stationary phase
    • The accumulation of waste products and scarcity of resources causes the population to enter the decline (exponential death) phase
  6. Endospores
    • Highly resistant structure formed by Bacillus and Clostridium when nutrient supplies are low
    • A stress cell undergoes asymmetrical cell division creating a small prespore and a larger mother cell separated by the transverse septum.
  7. Prespore contains
    • Cytoplasm
    • DNA
    • Dipicolinic acid which stabilizes DNA and proteins
  8. Mother cell
    Matures the prespore into and endospore then disintegrates, freeing the spore
  9. Endospore
    • Resistant to heat and desiccation
    • Undergo very few chemical reactions
  10. Free spore contains
    • Cell membrane
    • Cortex
    • Spore coat - thick peptidoglycan
    • DNA
    • Protein stabilizer - EDTA, similar to Dipicholinic acid
  11. Spore formers
    • Mostly G+
    • Bacillus anthracis - anthrax
    • Clostridium botulinum - botulism
    • Clostridium tetanii - tetanus
    • Clostridium perfringens - gas gangrene
  12. Spores will survive
    2 hours boiling
  13. When will a spore germinate?
    When environmental conditions are again favorable, protective layers break down and the spore germinates into a vegetative cell
  14. Growth requirements
    • Temperature
    • Oxygen
    • pH
    • Pressure
  15. Temperature
    Each prokaryotic species has an optimal temperature for growth and about a 30� range of acceptable temperatures
  16. Psychrophiles
    Grow optimally below 15�C, and make up the largest portion of all prokaryotes on Earth
  17. Thermophiles
    Multiply best around 60�C, living in compost heaps and hot springs
  18. Hyperthermophiles
    Are Archaea that grow optimally above 80�C, found in seafloor hot-water vents
  19. Mesophiles
    Thrive at the medium temperature range of 10� to 45�C, including pathogens that thrive in the human body
  20. Oxygen
    • Many prokaryotes are obligate aerobes, which require oxygen to grow.
    • Streptococcus
  21. Anaerobes
    • Clostridium
    • Do not or cannot use oxygen;
  22. Obligate anaerobes
    Are inhibited or killed by oxygen
  23. Facultative prokaryotes
    Grow either with oxygen, or in reduced oxygen environments
  24. Thioglycollate broth
    Can be used to test an organism�s oxygen sensitivity
  25. Carnophilic bacteria
    Require an atmosphere low in oxygen and rich in carbon dioxide
  26. Microphilic bacteria
    Likes a small amount of oxygen
  27. pH
    The majority of species grow optimally at neutral (~7.0) pH
  28. Acidophiles
    • Acid-tolerant prokaryotes
    • For example, those used to turn milk into buttermilk, sour cream, and yogurt
  29. Hydrostatic and Osmotic Pressure
    • Barophiles can withstand incredibly high hydrostatic pressure
    • For example, psychrophiles living at the bottom of the ocean
  30. Halophiles
    • Are salt-tolerant prokaryotes
    • They can maintain optimal osmotic pressure without suffering from plasmolysis
  31. What materials are used to grow bacteria in the lab?
    • Broth
    • Living Tissue
    • Agar
  32. Agar
    • General Purpose
    • Enriched
    • Selective
    • Differential
    • Synthetic
  33. General Purpose Growth Medium
    A complex medium is a chemical unidentified medium such as a nutrient broth or nutrient agar
  34. Living tissue
    Primarily for growing rickettsia
  35. Synthetic medium
    • In a synthetic medium, the chemical composition of the medium is known
    • Each amino acid is added individually
    • Primarily for genetic research
  36. Selective medium
    • Contains ingredients to inhibit growth of certain species and allow the growth of others
    • SS agar = Salmonella & Shigella
  37. Manitol salt agar
    • Will only grow staphylococcus.
    • Contains phenol red dye.
    • Staph aureus produces acid and turns dye yellow
    • Staph epidermidis does produce acid, so the dye turns redder.
  38. Differential medium
    Contains specific chemical to indicate species that possess or lack a biochemical process
  39. Enriched medium
    • Some "fastidious" organisms require an enriched medium containing specific nutrients
    • Blood
    • Cooked blood (chocolate)
  40. Can all prokaryotes be cultured?
    Many prokaryotes cannot be cultured in a laboratory
  41. Pure culture
    A pure culture is a population consisting of only one species of prokaryote
  42. Pour Plate
    • The pour-plate isolation method allows separation of species through dilution of a sample
    • Molten agar is poured over a culture in a culture dish
  43. Steak plating
    • Method for isolating colonies
    • The streak-plate isolation method spreads out individual cells to form discrete colonies of species
  44. Population grows measure 3 ways
    • Turbidity - cloudiness
    • Direct measurements - actually count
    • Indirect methods - measure dry weight of the cell population to get an indication of the mass. Oxygen uptake in metabolism can also be measured as an indication of metabolic activity.
  45. Standard plate count
    • In the standard plate count procedure, colonies grow on a plate containing a sample of diluted broth
    • The number of colonies indicates the original number of viable (living) cells in the broth