Week 5
Posted by drstocksblog on September 26, 2009
Exercise 7 — Microbiological Media and Aseptic Technique
Microbiological media comes in three forms: broth (liquid), semisolid agar, and agar (solid)
- Trypicase soy broth and agar are the nutritionally the same; the latter has agar added (15 gm/l) to make it solid.
- Remember that agar alone has no nutritional value for most bacteria; it is just a solid medium to which nutrients must be added to support bacterial growth.
- You can find a listing of kinds of media that we use and their composition in the introductory module in Vancko Hall Lab.
- Broth is usually dispensed in tubes and it is what we use for our pure cultures of bacteria.
- Semisolid agar is usually dispensed in “deep” tubes — about 10ml per tube. It is used for detecting motility.
- Agar may be dispenses in tubes as agar deeps or slants (allowed to cool at an angle so a slanted surface forms) or into plates.
You will take one of three available species of bacteria and aseptically transfer it to one tube of broth, one tube of semisolid agar, and one agar slant. You are inoculating these sterile media. The three species are:
- Staphylococcus aureus
- E. coli
- Proteus vulgaris
Aseptic Technique enables you to safely transfer bacteria from a culture to a sterile medium without contaminating the culture with another bacterium and without contaminating you or your work place. It is second only to the use of the microscope in importance in microbiology.
Be sure to read the lab book AND the comic book on this laboratory exercise. You may even find it helpful to print the comic.
Exercise 8 — Isolation of Soil Bacteria
The bacteria found in soil often form resistant structrures called endospores. These resist drying and other hazards (like oxygen if it is an anerobic organism).
- In this exercise you will heat a soil sample to kill any vegetative (living) cells that are present and presumably leaving on the endospores.
- After heating you will inoculate a tube of specialized medium (thioglycollate medium) which promotes the growth of anaerobes.
- Next week you will stain your soil cultures.
