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We're homeschooling and the Biology teacher sucks.
February 8, 2012 11:47 AM   Subscribe

Can you help me show my children some bacteria in our ancient microscope, and maybe go on to perform Science upon them? (The bacteria, not the children!)

We homeschool our three boys (ages 7, 9.5, 12.5) and we'll be talking about the Black Death next week. I'd like to use this opportunity to branch off into science a bit, discuss infectious diseases, basics about bacteria, etc. It would score major points with my boys if they got to see Real Live Bacteria through our microscope.

Unfortunately, my track record with the scope is pretty bad, as in, "I've never seen anything smaller than a grain of salt with it." It's my old Edmund Scientific student microscope, pretty much exactly this one. 10x eyepiece, rotating selector with 5x, 15x and 30x objectives, swivel mirror "light source" and rack & pinion focuser. I honestly don't know if the problem is my scope's magnification range, or sample prep, or operator stupidity.

Ideally, I'd like to be able to prepare a few samples of bacteria taken from, say, somebody's nasal mucus with a Q-tip; culture said bacteria for a while so that the population density works in our favor; view the samples successfully, maybe even ID some of the wee beasties?; and then perhaps expose the samples to different substances (lemon, garlic, soap, control?) and see whether they affect the bacteria.

Oh, right, the questions:
  1. Is my scope the right tool for the job, or can it be made so?
  2. How does one successfully culture bacteria?
  3. Viewing tips?
  4. Other suggestions from those more experienced than I?
  5. What safety practices should I model?
Thanks!
posted by richyoung to Science & Nature (13 answers total) 5 users marked this as a favorite
 
You should be able to swab your cheek and get bacteria. Are you staining it and putting it under a slide?
posted by empath at 11:51 AM on February 8, 2012


Honestly, I think this is going to be somewhere between extremely hard and impossible using that microscope. Don't even attempt it without doing some kind of stain. If you've had trouble finding things the size of eukaryotic cells in the past, finding bacteria is going to be very VERY frustrating. If you are hell-bent on trying, I'd get it all set up and in focus the night before the lesson so that all you have to do is flip on your light source.

As an alternative, find someone you know who knows someone who does any kind of biological research. Regardless of what that person actually studies, he or she will probably use bacteria in some capacity in his or her work (or know a dozen people who do) and might be willing to let your kids visit the lab.
posted by juliapangolin at 12:13 PM on February 8, 2012


How does one successfully culture bacteria?

Cotton swabs, petri dishes, growing medium, and a warm spot. You can buy bacterial culture kits online that are aimed at precisely this sort of thing.

Viewing tips?

If you just want to see the bacteria culture grow and die, then the culture kits alone are fine. You'll get nice, big, gross bacterial colonies that are visible with the naked eye.

If you want to look at microscope slides then you'll be better off with staining, but in my experience dead, unnaturally-colored bacteria aren't very interesting to little kids. USB video microscopes are neat and allow "live" viewing but unfortunately most don't have the magnification power necessary to see individual bacteria.

It's my old Edmund Scientific student microscope, pretty much exactly this one.

Get a modern microscope with an LED light source. Also get a set of prepared slides as a backup, so the kids will definitely have something to look at.

(lemon, garlic, soap, control?)

I would also consider something that will definitely kill the bacteria, like rubbing alcohol.
posted by jedicus at 12:13 PM on February 8, 2012


Disclaimer: not a bio major.

To see the bacteria we looked at in school (e. coli, etc.), you need about 1000x total magnification. I recall that they're easier to see at lower magnifications (400 - 500x ?) if they're stained, but that's also a godawful messy process.

Growing up with a student microscope like you describe, I mostly observed protists (from pond water and the like). They're quite easy to see at 300x if you can get enough light.
posted by introp at 12:15 PM on February 8, 2012 [1 favorite]


seems like you're going to need a 100x objective (1000x when multiplied by the eyepiece) and LOTS of light...your stumbling block is that bacteria (in general) are really really small...if your body cells were about the size of a softball, then they are about the size of rice grains. it's generally easier to see them when they form large colonies. often they can be identified by the kind of colonies that they form...kind of a gross answer to number 2 (haha)...don't clean the toilet for a week or so...see that greyish/brownish/orangey film on the sides of the bowl? you have just cultured some bacteria! yeast works really well too...it's bigger, you can buy a pack at the store and add sugar and warm water...check it every 10 minutes or so...good luck!
alternately, try adding some dirt to warm sugar water and see if anything grows...
posted by sexyrobot at 12:17 PM on February 8, 2012


I suggest purchasing some prepared slides of bacteria so you know what your microscope is capable of with that size of critter. I just linked to Carolina but there are tons of places to order slides from - all about in the same price range. The prepared slides will be made with specific stains. Microbio 101 involves gram staining.. here is an other Carolina kit. You can also check out Flinn or Wards (or many others - this is just where I ordered from). Once you know if you can/how to find the bacteria with your scope, you can do some staining and identification, and then probably if you can culture anything off your own person, you will likely just be able to say "Oh, this one from my hand is similar in shape to the one we saw on... "

Another type of cell students find hard to "see" at first are red blood cells. Especially if they try to make their own slides. Interesting challenge and an interesting comparison for cell sizes (RBCs are small but eukaryotic and prokaryotic bacteria are tinier.)
posted by adorap0621 at 12:17 PM on February 8, 2012


A fun experiment that you didn't ask about is to try to culture bacteria from different places around the house. Get yourself an agar plate, divide it into 4 different quadrants. Then, send the kids around the house with cotton swabs and have them swab different regions. Then, put the plate in a warm spot and watch the bacterial grow over a few days. We did this when I was in high school, but I think it's totally the thing that younger kids would love. I was shocked by how much bacteria came from the "doorknob" swab and how little came from the "inside of the urinal" swab. Kill it all with alcohol when you're done.
posted by Betelgeuse at 12:18 PM on February 8, 2012


I would get yourself a good high school or university-level Microbiology lab manual. Benson's is pretty straightforward and understandable, and it walks you through the process of culturing bacteria, safety measures pursuant unto, and preparing your slides, a task which involves staining and a bunsen burner, but which is easy enough to learn. 300x is low for identifying bacteria, but you could probably see enough to help the oh-god-they're-all-over-us feeling sink in a bit. In terms of the scope not working as advertised, maybe if there's a university or community college nearby, you could ring up one of the biology faculty to see if they'd be willing to take a look at it, or else recommend a biology major who would check it out and run you through its paces for $20 or so.

Once you get it working, let them mess around with pond water, too. That magnification should be fine for hours upon hours (if your kids are like I was at that age) of watching our little unicellular friends swim.
posted by notquitemaryann at 12:20 PM on February 8, 2012


Follow-up to my above answer: I ran across this while doing a curiosity search. It has a large list and pictures of bacteria and protists you may find, information on how to collect stagnant water, how you could grow your own in a jam jar, etc. Very shiny.
posted by introp at 12:21 PM on February 8, 2012


If you google, you will find plenty of kits that allow you to grow bacteria. I found this one for 15 bucks. You apparently can also order samples of different bacteria here.

At 300x magnification, you will probably not see much with your particular microscope, as everyone else has said. If you do want to try to see individual bacteria rather than the colony that you grow with the kit, I would recommend that you use a q-tip or toothpick, pick a culture from your plate, and then streak it across a microscope slide. Alternatively, you could put some of the bacteria in saline, place a drop of that on your slide, and look at them that way. Using 300x, I wouldn't expect them to look like anything more than a little bit of dust, unfortunately.
posted by nasayre at 2:01 PM on February 8, 2012


I love bacteria. I studied them for about 7 years. But, they are so boring under a light microscope, if they are unstained and under a low (less than 1000x) magnification. They only get a bit more interesting at higher magnifications, in my opinion.

You might be interested in Betsey Dyer's "A Field Guide to Bacteria". It is a bit more in-depth than you probably need, but it focuses on how to identify bacteria using signals from the environment, instead of a microscope. She also discusses how to culture bacteria either using baby food jars + nutrients + (agar or gelatin), where the nutrients can be pretty much anything that isn't too rich. (Too many nutrients will result in more pathogenic bacteria and will culture a lower number of species). (All of this must be sterilized, which is the hard part). An alternative project would be to build a Winogradsky Column, which results in colored bands of different bacteria types. Feel free to Mefi-mail me if you want some help with this.

Protists (single-celled Eukaryotes, so larger cells, and more related to plants and animals than bacteria) are much easier to see under the microscope, and much more interesting. While they do not cause plague, some can cause Giardia and the STI Trichomoniasis. Handling protists is also much safer than handling cultured bacteria (although one can work with bacteria safely very easily -- nothing to be afraid of with the right practices).

Your questions:

1) Your 'scope is not designed to see bacteria, and it will be quite hard to see them. You would need a better light source and (a phase contrast lens or to stain the bacteria).

2) One can culture bacteria with sterilized baby food jars and either sterile nutrients or just one the surface of a freshly sliced potato, placed into a sterilized baby food jar.

3) Viewing tips -- Use a stained sample, or concentrate on protists would be my advice, because they look like aliens, and most bacteria samples look like a clump of dots/rods/spiral-like shapes. Scientists who study bacteria look at them under a microscope far, far less often than people think.

4) See above.

5) Wash hands before and after handling anything that might have touched the bacteria. Use rubbing alcohol to kill off things. Place waste in bleach to kill anything on it. Use sterilized toothpicks or Q-tips to interact with the bacteria cultures -- never your hand. (bake things in an open jar with aluminum foil taped loosely over the jar opening. It isn't 100% sterile, but it is close).

This is a hard topic for even high schools, because of the lack of equipment. Good luck!
posted by Peter Petridish at 2:31 PM on February 8, 2012 [3 favorites]


Thanks, everyone, for the great answers. I learned at least one thing I didn't know from each one of you.

Based on your input, here's what I'm planning:

- I've put "A Field Guide to Bacteria" on hold at the local library.
- I like the idea of naked-eye observation of bacterial colonies; we'll get some agar (and probably petri dishes, too, since we don't have a supply of small jars)
- Definitely will be running the "samples from different parts of the house" experiment Betelgeuse describes.
- If I can find a more powerful eyepiece for my microscope, I'll try some prepared slides and, ideally, gram staining some stuff with my oldest.
- If I can't boost our magnification, I'll still give yeast and red blood cells a try (using whatever flashlights/bike lamps/desk lamps we can bring to bear on the stage). I can't really afford a more powerful scope than the one I have, so it's either a better eyepiece or nothing :^(
- Whatever we do, I plan to use this as a chance to introduce the parts of cells, the different classes of single-celled organisms, the concept of exponential growth, etc.

Thanks so much for taking the time to provide such detailed answers!
posted by richyoung at 7:44 PM on February 8, 2012


-red blood cells are also kind of on the small side...smaller than most body cells...still worth a try tho...the easiest cells to aquire are cheek epithelial (skin) cells...take a cotton swab and drag it along the inside of your cheek, using firm pressure, then wipe it on a slide.
-direct sunlight is going to be stronger than most lamps...using both works even better. keep some distilled water and an eyedropper handy to keep your slides from drying out. cover slips work too, but will squish your cells flat...which can make some cells easier to examine, but will smoosh things that are trying to swim around, like paramecia.
-pond water is your friend...use a long straw or pipette to draw water from the bottom, and fill another jar at the surface. different organisms will congregate at each location. you can use a piece of raw meat tied to a string and left overnight at the bottom as 'bait'...rotifers, tardigrades, amoebas, and flatworms are often found hiding in the muck at the bottom...paramecia tend to swim all over, and algae tend to hang out near the top
-if you're looking for a 100x objective or prepared slides at carolina biological or wherever, you should check out their live samples as well. Volvox, in particular, can be a bit hard to find in the wild and is well worth buying live, as it is incredibly fascinating to watch, as well as being an awesome example of a colonial organism.
-onion skin has HUGE cells, and takes a stain really well.
posted by sexyrobot at 9:04 PM on February 13, 2012


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