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2011-02-27 12:59:06

lab exam #1 info
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  1. What does colonty-forming unit refer to?
    • cells that have been sufficiently isolate & are growing from their original cell type
    • it's the cell or group of cells which reprodcue on a plate & result in a visible colony
  2. what are the 5 basic categories of colony morphology?
    • Shape: round, irregular, punciform
    • Margin: entire (smooth w/ no irregularities), undulate (wavy), lobate (lobed), filamentous, or rhizoid (branched-like roots)
    • Elevations: flat, raised, convex, pulvinate (very convex), and umbonate (raised in the center)
    • Texture: moist, mucoid, dry
    • pigment production (color): opaque, translucent, shiny, dull
  3. What does fastidious mean & where do autotrophs & heterotrophs fit in?
    • Fastidious: an organism that relies heavily on the enviro to supply ready-made organic compounds
    • Autotrophs require the least assistance from the enviro to grow, so they are not fastidious
    • Heterotrophs require preformed organic compounds fromt he enviro, so they are fastidious
  4. What is the germ theory of disease?
    • The germ theory of disease is a theory in biology. It says that small organisms (called germs), also known as microbes, are the cause of many diseases. The prevailing majority of the diseases are infectious. Today's view of how disease happens is that those small organisms cause a reaction in the body of those affected by a disease.
    • Louis Pasteur showed that this theory was true. He made an experiment w/ fermentation. In one case, he made a broth that he isolated from the surroundings, so no particles could pass to it from outside. the broth he thusly made did not change, and no fermentation took place. The other case was a similar borth, but this time, it was connected to the enviro. this time, fermentation toook place. The thing that caused fermentation therefore needed to come from outside (the enviro)
  5. How does one determine total magnification?
    Total magnification= magnification by the objective lens X Magnification by the occular lens
  6. Define the limit of resolution.
    • The limit of resolution (aka resolving power) is an actual measurement of how far apart two points must be for the microscope to view them as being separate.
    • Resolution improves as the limit of resolution is made smaller
    • The best limit of resolution achieved by a light microscope is about 0.2 um (its the absolute best)
    • A light microscope cannot distinguis between 2 points closer than 0.2 um
  7. Define and explain the improtance of the following in reference to the gram stain: decolorization & primary stain
    • Decolorization:
    • occurs between the applications of 2 basic stains, is the most critical step in the procedure
    • gram - cells are decolorized w/ alcohol or acetone but gram + stains are not
    • The alcohol/acetone in the decolorizer extracts the lipid, making the gram - cell wall more porous and incapable of retaining the crystal violet iodine complex, thereby decolorizing it
    • The gram + cell wall is less susceptivle to decolorization because it has a thicker peptidglycan layer & greater degree of cross linking (because of the teichoic acids) which traps the crystal violet-iodine complex more effectively

    • Primary stain:
    • although the gram stain has many variations, the primary stain is crystal violet
  8. define & explain the improtance of the following in reference to the gram stain: iodine & counterstain
    • Iodine:
    • added to crystal violet as a mordant to enhance crystal violet staining
    • by forming a crystal violet-iodine complex. this is right before
    • decolorization.

    • Counterstain:
    • gram - cells are colorized by the counterstain safranin. If the staining is succesful they will be reddish pink
  9. define & explain the importance of the following in reference to the gram stain: gram - & gram +
    • Gram - cell wall:
    • They also have a higher lipid content and a thinner peptidoglycan layer than gram + cell
    • It is decolorized w/ alcohol or acetone which extracts the lipids and makes it more porous
    • once its porous, it becomes incapable of retaining the crystal biolet iodine complex and is thus decolorized

    • gram +:
    • not decolorized w/ alcohol/acetone
    • thick peptidoglycan layer & more cross linking so it holds the
    • crystal violet-iodine complex very well and is difficult to decolorize
  10. defien & explain the importance of the following in reference to the gram stain: sequence & results
    • sequence:
    • The cells are tained w/ crystal violet- idoine complex
    • they are then decolorized w/ alcohol or acetone
    • gram - stains will be decolorized
    • gram + will not
    • after this safranin is applied

    • results:
    • gram += purple
    • gram -= reddish pink
  11. what is present in a cell wall to make an organism acid-fast?
    Mycolic acid- waxy substance that gives acid-fast cells a higher affinity for the primary stain and resistance to decolorization by an acid alcohol solution
  12. What is the difference between differential and selective media?
    • Selective: encourages growth of some organisms and discourages growth of others
    • Differential: allows us to distinguish between different microbes. Has 2 sub categories. Defined or chimically defined: each ingredient is known and in exactly what amounts. Undefined or complex: contains one or more ingredient made up of known ingredients, but of unkown composition (such as yeast, beef extract or digest of gelatin)
  13. Mannitol salt agar- what component makes it selective & what species of bacteria is it used to isolate? what makes it differential?
    • selective: Sodium chloride makes the medium selective because its concentration is high enough to dehydrate & kill most bacteria.
    • isolates: S. aureus
    • differential: mannitol provides the substrate for fermentation
  14. what component of phenylethyl alcohol agar is inhibitory to gram - and how does it work?
    phenylethyl alcohol is the selective agent that inhibits gram - organims by breaking down their membrane permeability barrier, thus allowing influx fo substances ordaniarly blocked and leakage of large amounts of cellular K. this ultimately disrupts or halts DNA synthesis
  15. Eosin methylene blue agar is used to isolate what?
    fecal coliforms
  16. MacConkey agar is used to isolate what organism? what sugar is found in the media?
    Isolates & differentiates members of the enterobaceriae based on the ability to ferment lactose
  17. Phenol red/purple broth: understand that fermentation of different carbohydrateds depends on which is added to the broth. what is the color/ph relationship? what is the indication of fermentation? what is the point of the durham tube? what is the application?
    • phenol red is yellow below 6.8, pink to magenta above 7.4, and red is between 6.8 and 7.4
    • acid production from fermentation of the carb lowers the pH below the neutral range of the indicator and turns the medium yellow
    • gas production, also from fermentation, is indicated by a bubble or pocket in the durham tube where the broth has been displaced
    • the durham tube is added to the tubes as in indicator of gas production. Gas production, from fermentation, will cause a lil bubble or pocket in the durham tube where the broth has been displaced
    • application: phenol red broth is used to differntiate members of enterobacteriacase and to distinguish them from other gram - rods
  18. what does "mixed acid frementation" refer to?
    • Mixed acid fermentation overcomes the phosphate buffer in the medium and lowers the pH
    • The acids produced by organisms that are capable of mixed acid fermentation are usually stable acids whereas acids produced by other organims are unstable and convrted to more neutral products
  19. what does catalase do?
    Catalase convers hydrogen peroxide into water and gasseous oxygen
  20. at what point is cellular respiration does citrate play a role?
    • citrate, or citric acid, produced as acetyl conenzme A (from the oxidation of pyruvate or B-oxidation or fatty acids) reacts w/ oxalocatate at the entry to the Krebs cycle
    • Citrate then is converted back to oxaloacetate throguh a series of reactions, which begins the cycle a new
  21. what is the important component of the Simmons citrate media? what its its function?
    • sodium citrate= sole carbon source
    • ammonium phosphate= sole nitrogen source
    • function: test the organisms ability to use citrate as its sole source of carbon
  22. MMWR report. What is epidemiology, mortality & morbidity?
    • Epidemiolgy: the study of the causes, occurence, transmission, distribution, and preventionof diseases in a pop
    • Morbidity: sickness
    • Mortality: death