View Full Version : growing bacteria?

03-30-2011, 10:52 AM
We just started the last unit in Mr. Q's biology program on hygiene and health. Tomorrow we'll be doing a lab where we are supposed to grow bacteria on meat, but being vegetarians I need some alternatives. I don't have time to order a kit like Magic School Bus, so I'm wondering if anyone has any ideas for a quick growing bacteria medium?


03-30-2011, 11:09 AM
Petri dishes? But you would need the alum for it. Huh.

How about bread mold? That's different though. What's the purpose of the experiment? What concept do you want to illustrate?

03-30-2011, 11:19 AM
We had fun rubbing slices of bread over different parts of our home then placing the bread in baggies and watching the mold grow over a week or so. Is that along the lines of what you're looking to do?

Oh, we also marked the baggies to indicate what the bread had been rubbed on (i.e. "toilet", "kitchen counter", "door knob"), and then compared and contrasted the mold growth (which bread was moldier? Which bread was the least moldy? Which parts of the home were therefore the most sanitary and least sanitary? etc.).

This was a fun experiment that my son thoroughly enjoyed!

03-30-2011, 11:31 AM
I didn't give very much information, did I? Hmmm, trying to do too much at once, perhaps? :)

We are supposed to test the effectiveness of antibacterial soaps. The suggested test requires smearing a cotton swab that's been rolled over raw meat onto some set-up gelatin, and sticking it a baggie for a few days. Another part of the test uses antibacterial soap/sanitizer swabbed on another sample of gelatin, and a third uses both. So I guess I need a medium that isn't meat but will grow bacteria pretty quickly.

I like the bread idea too--sounds fun (at least, to little boys!). Although, my son would probably go on a cleaning kick, or worse yet, suggest that I don't clean enough!

SueEllen Grieves-Curl
03-30-2011, 01:22 PM
bacteria will grow on almost anything given the right conditions. Bread is a good substitute.
You could just get a small piece of meat from anyone just for this one item and so you kids can have just another reason to NOT eat meat. As meat tends to have bacterias that veggies do not. And the second part being what bacterial anti bacterial will kill.

03-30-2011, 02:10 PM
It sounds like what you want is something to collect germs from, not something to grow them on - a replacement for the meat, not the gelatin. If this is the case, I suggest the toilet. That's where we collected from when the kids did petri dishes this year (Dea for Biology, Jay for a study of germs). The sink drains can also be fairly germ-filled.

03-30-2011, 02:14 PM
Well Brandi, that sounds sufficiently gross. :) Can I ask how you did that, exactly?

03-30-2011, 02:35 PM
We prepared their petri dishes - Jay's came in the MSB World of Germs kit & had agar we had to prepare, Dea's were Easy Gel petri dishes & had a special gel (different from agar) we had to prepare. Then, we put on rubber gloves, grabbed some cotton swabs and swabbed the toilet. You basically choose the most disgusting part of the toilet (this works best if it has been a few days since the toilet has been washed) - the rim, the outside (Jay sometimes misses the bowl & hits the outside instead), just under the rim where it's easy to miss stuff when you clean. Then we wiped the swabs in the petri dishes, carefully so we didn't mess up the gel/agar. For Jay, we also swabbed the kids toes (to see whose feet were dirtier), tested antibacterial soap by wiping his fingers on the agar before & after washing, and swabbed the inside of his mouth to test toothpaste. We stored the petri dishes in a cabinet (it said somewhere dry & cool). I posted some pics on my blog of the petri dishes. It's a bit hard to see Jay's, but Dea's were easier to see.

We also collected some water from the local river - just dipped an empty water bottle in & filled it part way. Then we used a dropper to put some of the river water in some of the petri dishes. We added antibiotic discs to the petri dishes, to see if they would kill anything. Those were the worst of the petri dishes we did. The antibiotic discs did nothing! The river water actually ate through the gel and there were disgusting red colonies growing all over in the dishes.

03-30-2011, 02:52 PM
Great--thanks! That gives me some good ideas.

03-30-2011, 03:07 PM
The mouth is also a huge source of bacteria. My daughter did a science fair project determining what had more: her mouth, the dog's mouth, and the cat's mouth. Her's had the most.......ewwww. We used plain gelatin for the growing medium. Just be sure to cover whatever you're using for the dish, or you may be collecting bacteria from the air.

03-30-2011, 03:24 PM
So, to use gelatin, do you just buy the plain stuff from the store and mix it up? And can I use any sterilized dish (does oxygen bleach work? or the dishwasher?) or does it have to be a petri dish? Sorry for the dumb questions...I've never done this before, and of course my son wants to do it NOW. We don't have a science store, so if I don't have to use "official" supplies, we can do the experiments sooner. Thanks!

03-30-2011, 03:36 PM
The regular, unflavored gelatin should be just fine & a dishwasher should sterilize a dish enough to do it. Any dish, as long as it is sterile and you have a way to cover it, should work.

03-30-2011, 03:37 PM
Yep.....what Brandi said.....

03-30-2011, 06:33 PM
Thanks! :)

03-30-2011, 09:42 PM
have fun growing stuff :)

wouldn't another good "meat replacement" be raw egg?

03-30-2011, 10:36 PM
Gelatin ought to work fine, yeah. I don't know this from personal experience, but my brother has a graduate degree in plant pathology and once synthesized his own unique strain of bacteria to combat fungus growth on tobacco leaves. I was in awe.