Micro 17 & 19

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Micro 17 & 19
2011-06-26 22:24:39
micro lab

Pour plate technique and determination of bacterial numbers
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  1. How do you read the volume in a calibrated plate?
    Read at the bottom of the miniscus
  2. Describe how you would perform the pour plate technique. Include the materials neede and how you would use them.
    • Stock broth culture, saline tubes, pipette, pipetter, pretri dishes, and tubes of melted agar
    • -1mL of broth culture is transfered to 1st saline tube with a pipette, specimen is mixed in the saline tube.
    • -1mL of saline mix in 1st tube is transferred to 1st petri dish, go back into the 1st saline tube and transfer 1mL of saline mix to the 2nd tube of saline and mix.
    • -transfer 1mL of saline mix in 2nd tube to 2nd petri dish go back into 2nd saline tube and transfer 1mL of saline mix to 3rd saline tube and mix.
    • -transfer 1mL of 3rd tube mix to 3rd petri dish, pour melted agar into each petri dish
    • -mix let cool to harden and incubate overnight
  3. Using the pour plate technique, describe how you would do a viable plate count. Include the materials needed and the limitation necessary to obtain an acceptable bacterial count. Also, what are the consequences of exceeding the required limitations.
    Use the same materials and techniques for the pour plate technique. Dilutions 1-100 to 1-1000 are made. As the agar hardens individual baterial cells are fixed and form colonies upon incubation. Surface colony counts should be between 100-200 CFU per plate. If below or to high (above 250 cfu per plate) then a statistical problem.
  4. Why are the surface colonies on a pour plate larger than those within the medium?
    • -More room to grow on the sruface than in the agar.
    • -toxic by products are diluted on the surface better
    • -more nutrients are available on the surface as the bacteria grows
  5. What are the three bacterial shapes and the proper names for each shape?
    • -Bacterial cocci is the proper name for spherical shaped bacteria
    • -Baccili is the proper name for rod shaped bacteria
    • -sprilli/spirochae is the proper name for corkscrew shaped bacteria