micro lecture ch 6

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micro lecture ch 6
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micro lecture ch6
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  1. Classify microbes into five groups on the basis of preferred temperature range.
    • psychrophiles (cold loving) 0-15 degrees C
    • psychotrophs (able to grow in cold temps but not as low as psychrophiles-food spoilage in fridge or freezer) 20-30 degrees C
    • mesophiles (moderate-temp-loving) 20-40 degrees C =most human pathogens
    • thermophiles (heat-loving) 45-80 degrees C =not very common
    • themoduric (contaminants of heated food) can survive in short exposures to high temp
    • Hyperthermophiles-(Archaea)
  2. Identify how and why the pH of culture media is controlled.
    • It is controlled because certain cultures will only grow at a certain pH so you need their nutrients to be at that pH.
    • You pH the solution the same way you would any solution: adding acid or base until you reach the desired pH.
    • Most bacteria grow best between pH 6.5-7.5
    • To neutralize the acids, chemical buffers are included in growth medium: peptones, amino acids, phosphate salts
  3. Explain the importance of osmotic pressure to microbial growth.
    • water=growth
    • Microbes need a certain osmotic pressure to maintain integrity and get nutrients
    • hypertonic environments, increase salt or sugar, causes plasmolysis (shrinks cells)
    • some bacteria like this, some dont
  4. Provide a use for each of the four elements (carbon, nitrogen, sulfur, and phosphorus) needed in large amounts for microbial growth.
    • all organisms require a carbon source; used for structure and energy
    • nitrogen is needed for amino acids to build protein and nucleic acid synthesis
    • sulfur is needed in amino acids- thiamine and biotin
    • phosphorus is extremely important to make DNA, RNA, ATP and phospholipids in membranes

    CHONPS
  5. Explain how microbes are classified on the basis of oxygen requirements.
    • On the basis of oxygen requirement microorganisms are classified as
    • Obligate Aerobes: organisms that require oxygen
    • Facultative Anaerobes: both aerobic and anaerobic growth; greater growth in presence of oxygen
    • Obligate Anaerobes : only anaerobic growth; ceases in presence of oxygen
    • Aerotolerant Anaerobes: only anaerobic growth; but continues in presence of oxygen
    • Microaerophiles: Only aerobic growth; oxygen required in low concentration

  6. Identify ways in which aerobes avoid damage by toxic forms of oxygen.
    1. Superoxide free radicals are a toxic byproduct of aerobic respiration. Aerobes have an enzyme called SOD (superoxide dismutase) that converts superoxide free radicals into water and hydrogen peroxide.

    2. Peroxide anion - a byproduct of the SOD reaction - is also toxic, so we have catalase to neutralize it.

    3. The enzyme catalase converts peroxide anion into into water and oxygen, and/or the enzyme peroxidase converts it into water.

    These 3 grab and break up the toxic forms of oxygen before they affect your cells

  7. Distinguish between chemically defined and complex media.
    • chemically defined medium is one in which the exact chemical composition is known
    • a complex medium is one in which the exact chemical composition varies slightly from batch to batch
  8. Justify the use of each of the following: anaerobic techniques, candle jars, selective and differential media, enrichment media.
    anaerobic growth media- reducing media chemically remove molecular oxygen that might interfere with the growth of anerobes. Petri plates can be incubated in an anaerobic jar (clamps closed tight with an envelope containing sodium bicarbonate and sodium borohydride to suck up the oxygen), anaerobic chamber (where you have a big glass box and you stick your hands in gloves to manipulate things inside) or OxyPlate

    candle jars-used to grow bacteria that require an increased CO2 concentration. jar with a candle inside along with the media

    selective media- by inhibiting unwanted organisms with salts, dyes or other chemicals, selective media allow growth of only the desired microbes

    differential media are used to distinguish among different organisms

    enrichment culture is used to encourage the growth of a particular microorganism in a mixed culture. by placing sample of thousands of other bacteria including the one you want to study, then you just add the "food source" that your bacteria likes until the one you want is the only one growing
  9. Define colony.
    • a visible mass of microbial cells that theoretically arose from one cell
    • a population of cells arising from a single cell or spore or from a group of attached cells
    • a colony is often called a colony-forming unit (CFU)
  10. Describe how pure cultures can be isolated by using streak plates.
    • A sterile inoculating loop is dipped into a mixed culture that contains more than one type of microbe and is streaked in a pattern over the surface of the nutrient medium. As the pattern is traced, bacteria are rubbed off the loop onto the medium. The last cells to be rubed off the loop are far enough apart to grow into isolated colonies
  11. Define bacterial growth, including binary fission.
    • binary fission-The normal reproductive method of bacteria is binary fission, in which a single cell divides into two identical cells.
    • budding-forming a smaller cell that breaks off from the original cells
    • conidiospores (actinomycetes)-A unicellular spore produced asexually by a fungus
    • fragmentation of filaments-breaking off filaments and it growing into a new cell

  12. Compare the phases of microbial growth and describe their relation to generation time.


    generation time is the time required for a cell to divide or a population to double

    most bacteria have a generation time of 1 to 3 hours; other require more than 24 hours per generation
  13. Explain four direct methods of measuring cell growth.
    • 1. microscopic count
    • 2. viable plate count
    • 3. membrane filtration
    • 4. most probable number

    • 1. microscopic count uses a coulter counter:
    • 2. viable plate count: uses serial dilutions

    • then inoculate petri plates from serial dilutions:
    • .
    • after incubation, count colonies on plates that have 25-250 colonies (CFU's)
    • caculation: number of colonies on plate x reciprocal of dilution of sample = n umber of bacteria/ml
    • ex: if 32 colonies are on a plate of 1/10,000 diution, then the count is 32 x 10,000 = 320 bacteria/ml in sample


    • 3. In filtration, bacteria are retained (stuck) on the surface of a membrane filter and then transferred to a culture medium to grow and subsequently be counted.


    4. The most probable number (MPN) method can be used for microbes that will grow in a liquid medium; it is a statistical estimation.


    • Multiple tube MPN test uses 15 tubes
    • Count positive tubes and
    • compare to statistical MPN table
  14. Differentiate between direct and indirect methods of measuring cell growth.
    • In a direct microscopic count, the microbes in a measured volume of a bacterial suspension are counted with the use of a specially designed slide

    An indirect way of estimating bacterial numbers is measuring the metabolic activity of the population (for example, acid production or oxygen consumption).
  15. Explain two indirect methods of measuring cell growth.
    • 1.turbidity: cloudiness, caused by cell growth; you're measuring the amount of light that passes thru

    2. dry weight: in this procedure, the fungus is removed from the growth medium, filtered to remove extraneous material, and dried in a disiccator. Then weighed.
  16. psychrophiles
    cold loving
  17. mesophiles
    • moderate temperature loving
    • most of human pathogens
  18. thermophiles
    heat loving
  19. psychrotrophs
    psychotrophs (able to grow in cold temps but not as low as psychrophiles-these cause food spoilage in fridge or freezer) 20-30 degrees C
  20. hyperthermophiles (extreme thermophiles)
    extreme heat loving archaea
  21. pH
    • the acidity or alkalinity
    • most bacteria grow between pH 6.5 and 7.5
    • molds and yeasts grow between pH 5 and 6

    • Acidophiles grow in acidic environments
    • Alkalinophiles (up to pH 10) ex: urea- decomposing bacteria like Proteus sp
  22. osmotic pressure
    the force with which a solvent moves from a solution of lower solute concentration to a solution of higher solute concentration
  23. plasmolysis
    shrinking of cell's cytoplasm due to hypertonic conditions
  24. extreme halophiles
    • archaea that require super salty environments
    • ex: Halobacterium sp.
  25. obligate halophiles
    • another name for extremem halophiles
    • requires salt to live
    • organisms that have adapted so well to high salt concentrations that they actually require them for growth
  26. facultative halophiles
    • can survive high salt conditions but is not required for survival
    • ex: staphaylococcus aureus

    organisms that do not require high salt concentrations but are able to grow at salt concentrations up to 2%
  27. obligate aerobes
    • organisms that require oxygen to metabolize
    • ex: most fungi, protozoa, and bacteria like
    • bacillus sp and
    • pseudomonas sp
  28. facultative anaerobes
    • can survive with oxygen present but does not require it
    • during minus oxygen states, anaerobic respiration or fermenation occurs
    • possess superoxide dismutase and catalase
    • greater growth in presence of oxygen

    ex: e. coli and s. aureus
  29. obligate anaerobes
    • cannot use oxygen for metabolism
    • does not posses SOD and catalase
    • the presence of oxygen is toxic to the cell

    ex: clostridium sp and bacteroides sp (can live in your intestines)
  30. aerotolerant anaerobes
    can survive in presence of oxygen; does not utilize it in any way

    • Facultatiave anaerobes are primarily aerobic and alternatively anaerobic, in other words they can grow with or without oxygen, but preferentially grow with
    • oxygen.
    • Aerotolerant anaerobes do not utilize oxygen, and is not affected by it
  31. microaerophiles
    requiring oxygen for growth but at lower concentration than is present in the atmosphere

    requires less than 10% of atmospheric O2

    ex: campylobacter jejuni
  32. organic growth factors
    organic compounds obtained from the environment
  33. culture medium
    • nutrients prepared for microbial growth
    • ex: tsa or tsb
  34. inoculum
    introduction of microbes into new medium
  35. culture
    microbes growing in/on culture medium
  36. sterile
    no living microbes
  37. agar
    Complex polysaccharide that cannot be eaten or broken down by microbes

    Used as solidifying agent for culture media in Petri plates, slants, and deeps

    Generally not metabolized by microbes

    Liquefies at 100°C

    Solidifies ~40°C
  38. colony
    a population of cells arising from a single cell or spore or from a group of attached cells

    a colony is often called a colony-forming unit (CFU)
  39. binary fission
    The normal reproductive method of bacteria is binary fission, in which a single cell divides into two identical cells
  40. generation time
    the time required for a cell to divide or a population to double is known as the generation time
  41. bacterial growth curve
    • A graphic representation of the growth of a bacterial population in which the log of the number of bacteria or the actual number of bacteria is plotted against time
  42. lag phase
    • the surprise phase
    • there is little or no change in the number of cells, but metabolic activity is high
  43. log phase (exponential growth phase)
    the bacteria multiply at the fastest rate possible under the conditions provided
  44. stationary phase
    there is an equilibrium between cell division and death
  45. death phase (logarithmic phase)
    the number of deaths exceeds the number of new cells found

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