Medium Prep

Question 1

outcomes

Answer 1

1. identify main differences between (solid & liquid media), (general & selective), (defined & undefined)
2. list need for and conditions necessary for sterilizing growth media
3. aseptically prepare solid growth media in petri dishes

Question 2

media

Answer 2

food for microbes
solid- in petri dish/plate
broth- liquid media

Question 3

agar

Answer 3

solidifying agent (like gelatin)
no nutritional importance
solid until 100 *C
safe & easy to handle
did not react chemically with other components of a medium

Question 4

sterilizing medium w/ agar

Answer 4

heat to 121*C in steam sterilizer (agar becomes molten)

Question 5

sterilization

Answer 5

kills all life to prevent any microbes from being in medium
autoclave = steam pressure cooker
heats to 121*C, held at temp for 15 min and 15 psi

Question 6

general media

Answer 6

any microbe will grow (majority of media)

Question 7

selective

Answer 7

only grows certain types of microbes

Question 8

differential

Answer 8

grows any type of microbe but they’ll look different

Question 9

defined medium

Answer 9

known & consistent chemical composition; does not contain any components that vary from batch to batch

ex: beef extract, peptones (aka hydrolyzed or partially hydrolyzed protein)

Question 10

procedure 1-5

Answer 10

1. label Erlenmeyer flask w/ symbol of your group so it can be identified
2. measure 250mL of deionized (filtered water w/out minerals) water using a graduated cylinder
3. pour about half water into flask
4. weigh out 10 g of tsa
5. add tsa to water in flask and swirl so majority is mixed

Question 11

procedure 6-10

Answer 11

6. add remaining water to flask, washing down any tsa from inside of flask
7. cover mouth of flask with foil & place into autoclave
8. label the bottom of each petri dish w/ TSA and group #
9. lay dishes right side up in a row and keep lids on until pouring plates
10. when sterilization is complete, put on oven gloves and remove flask from autoclave, let flask stand at room temp for at least 10 mins

Question 12

procedure 11-15

Answer 12

11. peel foil about halfway off flask
12. raise lid off one petri dish and hover it over plate (do not set on bench) and pour the hot medium to a depth of 5mm and immediately put lid back on
13. repeat for the rest of the 11 plates
14. all all medium to solidify
15. when medium is sold, invert plates (bottoms-up) place into 2 stacks, and place into designated storage area

Question 13

how would the media we made be classified

Answer 13

general, defined