DIY Micro

NDSU Microbiology
by NDSU Microbiology

Guest Blogger: John Schmidt, Undergraduate in Microbiology

While my growth media is solidifying in my fridge, I sit down to begin writing what is (at least for me) turning out to be an interesting blog entry. Originally, I intended to write about my lab coat. Yes, it was as boring as it sounds. So instead, I decided to kill two birds with one stone. I have long wanted to employ what I have so far learned about microbiological lab methods in my apartment, and I needed to generate a blog entry. I tracked down a recipe online for growth media (I’ll get to that in a bit), drafted a simple experiment, gathered the necessary supplies (mostly from Walmart, and shown in the top-left image), and got to work.

The experiment is to compare the relative cleanliness of myself and my roommate (who tolerates living with someone who will eventually become a mad scientist). I prepared growth media using the following recipe, found here: mix 4 cups distilled water, 4 packets of unflavored gelatin, 4 beef bouillon cubes, and 8 teaspoons of sugar; bring mixture to boil; remove from heat, then pour and let cool to solidify. I used plastic snack cups as petri dishes and labeled them as needed.

I have prepared 12 growth plates (top-right image) to streak from a variety of places: the inside door handles of our separate bathrooms, the fronts of our toilet seats, the outside door handles of
our rooms, the light switches in our rooms, and our computer mice. The two remaining plates will be streaked from my own throat (as positive controls). The streaks will be obtained from 2 inch swabs using Q-tips (except in the case of the throat swab). Finally, two more plates will remain un-streaked (as negative controls). I will let all media incubate for 24 – 72 hours in the towel closet of my bathroom, at about 28°C. The relative amounts of growth will be compared following incubation (including colony counts, if possible). I will attempt to be reasonably aseptic, using a can of sanitizing spray and latex gloves.

I have every faith that my roommate will “win” this experiment. He is much cleaner than I am.

So while science slowly plods along, let me take this opportunity to point out that this is how microbiology was conducted before centrifuges, ELISA, and gel electrophoresis. Even in a well-stocked lab,
we still use wire with a wooden handle to streak media onto plates that haven’t changed much over the last few decades. Ours is (to some degree) a low-tech profession, with more emphasis on creativity and good technique than the latest scientific gadgets. Not to say that those gadgets aren’t important: they allow us to gather information we might not otherwise acquire. But it’s a comforting thought to know that the old methods still have a place.

I like to think that Leeuwenhoek and Pasteur would be proud of me right now, one of their many intellectual descendants.

(1 hour later…)

Alright, so the growth media solidified pretty well, presenting a surface firm enough for proper streaking. They also seem to handle being inverted without concern for the media falling out. Streaking is now complete and the plates have been placed into my incubator (bottom-left image) at 3 PM on October 12th.

(1 unexpected hour later…)

So apparently the homemade media isn’t able to handle 28°C without liquefying. I suspect that the agar solidifying agent used in the lab tolerates a wider range of temperature. I have removed the plates
from the incubator and am going to let them stand at room temperature for the remainder of this experiment. Perhaps they will re-solidify. They will likely not have contiguous colonies, but cloudiness in the media may still be usable.

(23 hours later…)

The good news is that there is visible growth, appearing as wispy white “clouds” in the media (which did re-solidify). The bad news is that there isn’t yet enough of it to really make any comparisons. I have chosen to let them continue growing for another 48 hours, after which I’ll report whatever I have.

(48 hours later…)

It is now October 15th, three days after starting the experiment. I did get good visible growth on one plate, but unfortunately it was from an extra plate (not part of the original experiment) inoculated from my roommate’s old mouse. It produced quite a bit of mold after 48 hours of incubation (fuzzy bottom-right image; the red circles indicate growth), proving that the media does work. For the rest of my plates, the reversion to liquid and back to solid allowed only a few very small colonies to pop up. There isn’t nearly enough to compare cleanliness. Sorry to build the suspense.

But like a good scientist, I don’t count this a complete failure. I learned that gelatin has some limitations that agar doesn’t. I don’t know if this is how the nutrient agar we all know and love got its own start, but I suspect it was similar.

Now if you’ll excuse me, I need to learn how to build an autoclave.

This entry is part of the fall MICR 354 scientific writing students' blog series.


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