Yeast Lab day 2

Today was the day the students took their petri dishes that they had sprinkled yeast onto the agar in and made a wet mount slide from the yeast growth.  There was a great deal of bacterial growth as well, but I had them take their samples from the fungal growth and use aseptic technique in their handling.  The slides they made were great!  I did not have them heat set this year.  We did use a cover slip, and then we added the immersion oil to the top of the cover slip.  Each group was successful with this method.  I had to make up some 70% ethanol at the last minute because I had forgotten to check the bottles left in the lab over the summer.  We had used almost all of it last spring semester, so I mixed some up quickly this morning and refilled the bottles.

Jobs for the lab tech today: Finish refilling all of the bottles of 70% ethanol, fill up the distilled water bottles in the lab for the new semester, cleaned the 40X and 100X objectives on all scopes, got one round of old culture tubes ready to sterilize when I run the autoclaves on Wednesday, and cleaned a round of used slides that had soaked in clorox water.

On Wednesday, I need for her to make at least another 1600 mL of nutrient agar to have all the kids will want on Thursday for the Collection of Microbes lab.  She can also help me pour those plates and begin to clean out the test tubes after they have been autoclaved.

Yeast Lab Followup

I need to order some 7" balloons before I do this lab again.  Since Party City went out of business, I haven't been able to find that size.  I purchased 9" balloons, and they are acceptable, but we did not have the excitement of small explosions occasionally around the room like I have had in years past.  The kids love it when that happens!

Initial Setup

I also told second period to fill their tubes up to within about 1" of the top which will allow for more dramatic results.

Different Lab Group, but results after 25 minutes

Is Yeast Alive? First Lab of the New Semester

I almost messed up today!  Tomorrow is the first lab of the new fall semester--a lab titled Is Yeast Alive?  I got this lab on the internet a couple of years ago and have used it as the first lab every semester since, but I almost had an epic "fail" on my hands tomorrow which would not have been a great way to start a semester! There are two parts to this lab, one a test for metabolism (cellular respiration producing carbon dioxide gas that will fill up balloons) and the second a test for growth.  I remembered to buy balloons yesterday, although I only found 9" balloons, not 7" which I think is what I have used in previous semesters.  I hope those will be OK.  Today when I went to make copies of the lab for my students, I remembered that I also needed Petri dishes of nutrient agar for the second part.  I had not planned on making agar today, but frantically got everything mixed up and into the autoclave in time to get it processed and hopefully poured without staying too late.

My autoclave is a highly manual (as opposed to automated) version that is really just an overgrown electric pressure cooker and the entire process takes approximately 2 1/2 hours to complete.  There is no thermostat which regulates itself--someone must stay with the autoclave at all times once it comes up to pressure to be sure that it doesn't overheat.  If you are lucky, you can get the gauge set to where it will toggle on and off within the appropriate range, but I still will not leave it unattended.

Anyway, I mixed up 1600 mL of nutrient agar in two 1000 mL Erlenmeyer flasks (18.4 g of nutrient agar powder to 800 mL water in each to avoid boiling over), let the mixture stir and then placed both flasks with lids loosely screwed on into the autoclave to sterilize.  I had a new lab tech student helping me today, so even with teaching her how to pour plates, I was able to pour 74 plates from the agar I made.  

I did  finally have to buy new yeast this time.  I had my lab tech check the viability of the yeast that had an expiration date of October 2011 on it.  And, as expected, the foaming action was not what I had hoped.  New yeast this semester!  I'll be going to Publix after school today to try to buy another container of yeast.  I don't want to use the packets, but I may have to.  I need 4 grams per lab station, so I will need at least 56 grams.  Well at least that's an excuse to go visit our new Publix grocery that just opened up here in Knoxville.  LOVE that store!  I also had the lab tech place four balloons in each of the white baskets that hold student supplies for lab.  I'll just have to replenish them between 1st and 2nd block.

I am going to try to revisit and update this blog with each lab this semester.  I hope it will be beneficial to others and especially to someone here at my school if I end up somewhere else sometime in the future.  At that point, someone else would have to step in and teach Microbiology.  This blog should be a big help to them if that should happen.

Is Yeast Alive? Lab

This is the first lab I run every semester because it can be done with just yeast before fees have been collected to purchase organisms with. This semester, I bought two different kinds of water balloons at Wally World. The ones that come in the large plastic container (kind of like a tennis ball container) were TOO small to even fit over the mouth of the test tubes. The other ones didn't work very well either. I think last semester, I just bought small regular balloons and these seemed to work better.

One change I made to the procedures on Part 1 was to mix the yeast and water in a beaker instead of trying to mix it in a test tube. This cut down on prep time for the kids and worked just as well. They then just evenly distributed the yeast mixture into the four test tubes. I will do this again, so I need to change the procedures before printing them out next semester.

One student asked me how we knew that the production of the gas was an indication of life instead of just an indication of a chemical reaction. I told him that is one reason we are doing Part 2 of the lab also (which will show evidence of growth).

Infectious Disease Simulation

This activity was great fun and really drove home how rapidly infectious disease can spread throughout a community. I used the small plastic beakers instead of buying Dixie cups and they worked fine. After each round, I had students clean out their cups well and return them to the front demo desk where I refilled them with either water or .1M NaOH (only one cup). We actually had time to run through the lab enough times to where they did 5 interactions on the last round which infected all but about three people in the classroom, which was pretty powerful. Great Lab!

Differential and Selective Media Lab

This lab worked beautifully! We used Staphylococcus epidermidis, E. coli, Serratia marcescens, and Enterobacter aerogenes. All of them responded exactly as expected.

MacConkey and EMB agar

Next week's lab on Differential and Selective Media calls for MacConkey and EMB agar. I made 800 mL of both this morning.

MacConkey--40 g powder in 800 mL of distilled water

EMB agar--28.8 g powder in 800 mL of distilled water

Both required heating and stirring until dissolved.

I only had 100 g of each of these powders, so if I have two sections of Micro in the fall, I will need to order a bottle of each.