Week 7
TUESDAY: Exercise 10 — isolation of bacteria
Finish this exercise by examining your streak plates.
- Ideally you should see well isolated colonies at the end of the second were beginning of the third section on your plate of agar.
- on the TSA agar can you see more than one kind of colony?
- If you did not get good isolation talk to your instructor about what you might do to improve your technique.
- Be sure to look at and draw all three kinds of selective media.
- Review and be sure that you understand whether each of these kinda of agars are also differential. If they are differential be sure to know what they are differential for and how you interpret the results.
Assignment in lab on Tuesday:
- Prepare a gram stain from an isolated colony on any medium except eosinmethylene blue agar. (why can’t you do an accurate Gram stain this kind of agar.
- On a piece of paper separate from your lab manual
- draw and label the streak plate that you are using.
- draw, label, and describe the results of your gram stain. (Don’t forget to draw your control!)
- briefly tell if your Gram stain confirms (or not) that you have successfully isolated a species of bacteria.
- Hand in both your drawing, explanation, and your labeled slide before leaving the lab.
- Your effort is worth 10 points
THURSDAY: begin Exercise 11 — Project one — Morphological Unknowns
In preparation be sure to read exercise 11 in your laboratory manual.
Your Task (document everything with notes and drawings)
- Isolate each bacterial species by growing them on trypticase soy agar.
- Determine the following for each species:
- Their colony characteristics.
- Their shape and arrangement of cells.
- Their gram stain characteristics.
- Their motility.
- Document each of these characteristics with digital drawings or pictures.
- Write up your report and hand it in on time.
- You will have until Friday March 26th to work on your unknowns.
- Your report is due at the start of your lab session on Tuesday March 30th.
Pick a test tube containing your unknown bacteria. It contains two different species which are visibly different with the gram stain.
- Be sure to record the number of your unknown on the paper provided as well as in your laboratory manual.
Today you should do the following:
- prepare to streak plates on trypticase soy agar plates. One will be incubated at 37° C. and one at 25° C. (Some bacteria will grow better at one temperature than at the other.)
- prepare two slides from your unknown for gram staining. (At least heat fix the slides and store them for staining later.)
- Fresh cultures stain better — so it is best to prepare these slides for staining today!
- do a hanging drop or wet mount preparation to determine if your unknown is motile. You do not need to draw motility because it is hard to capture in a drawing. You should, however, describe it.
Be sure to take good notes on what you have done. You will need too refer to your notes and drawings when writing up your report which is worth 100 points!
After you are done for the day place your unknown culture in the designated rack; it will be refrigerated and available for you to work on next week.
Day 1
- Isolate: 2 streak plates — one incubated at 37 degrees C, the other at 25 degrees C.
- Characterize from the broth cultures:
- Motility — hanging drop or wet mount
- Gram stain — prepare at least two slides for gram stains of you unknown.
- If you don’t get to stain or look at them, that’s OK. But be sure to make the slides today while your cultures are fresh.
