How Would Mr. Wizard Make A Pitri Dish Lab?

January 25, 2009 10:37 AM

What's the best way to do a pitri dish culture of a bacteria, to determine its positive/negative response to a variety of applied substances?

Suppose that a person living in the third world wants to have a homemade pitri dish lab, to culture some bacterial infection. The goal would be to try out a variety of antibiotics, chinese folk medicines, herbs, juices, whatever, just to see how the bacteria responds to each one positive/negative. Can the pitri dish lab be made from stuff available in the supermarket? How can it be done? Whether or not the pitri dishes can be made or bought - how to do the experiments?

posted by peter_meta_kbd to science & nature (6 comments total)

You can find recipes for bacterial growth media on the internet and buy the glass ware (petri plates, flasks or test tubes), a pressure cooker can be used to sterilize the equipment and contaminated media.

There are two basic experimental setups you can use. The first involves spreading dilute bacterial culture evenly over the surface of a plate and placing paper circles that have been soaked in the substance you want to test on the surface. If the bacteria are killed by the substance you will see a clear zone around the paper. The second setup uses liquid media and serial dilutions of the substance to be tested (1mg/ml, 100ug/ml, 10ug/ml, 1ug/ml etc). You inoculate a tube of just media, the dilutions of the substance and have one uninoculated tube as a reference. The lowest dilution which doesn't show any growth (as measured by turbidity) after 24 hours is the minimum inhibitory concentration MIC of the substance.

Before you begin there are a several of problems.
You need to isolate and identify individual bacterial species.
Different bacteria need different conditions to grow
Working with infectious bacteria is dangerous to yourself and others especially since you will end
up with resistant strains.
Working with infectious bacteria outside of a licensed inspected lab may be illegal. Think bioterrorism.
posted by colophon at 11:27 AM on January 25

If you don't know basic lab safety, you shouldn't be culturing anything, much less bacterial infections--you could easily wipe out your whole family in a matter of days. If I were you, I'd take classes at a community college and learn biochemistry and lab techniques from the ground up. Not to mention the fact that if you live in Indonesia and try to do any of this outside the system, you're likely to get on every bioterrorism watch list from here to kingdom come.

That said, the best resource on biological experiments I know is a British grad student posting under the name of "Megalomania" at the Rogue Science Explosives and Weapons forum. Scroll down to their "Chemistry for Amateur Experimenters and Citizen Scientists." Lots of great resources if you don't mind the company of people who make nerve gas for fun.
posted by aquafortis at 1:05 PM on January 25

What colophon said, plus sterilization, sterilization, sterilization! It's hard enough to isolate a specific species, prove it is what you say it is, prove it's involved in whatever illness/condition you're interested in, and then go about conducting studies on it in a controlled environment with modern lab equipment. Failure to properly sterilize everything in a bacteria lab is grounds to throw out a whole study, good luck replicating those same conditions in a tent or apartment without a bio safety hood.

You can actually come pretty darn close to bacteria growth medium using commonly available ingredients, but getting the solutions right is going to be tricky. That's why microbiologists don't spend days producing media from raw products and instead just order a dry mix from a company like Fisher or Sigma Aldrich, add water, and sterilize it.
posted by Science! at 1:11 PM on January 25

If you're just trying to test the general antibiotic properties of various substances, you do not want to culture a "bacterial infection." Non-disease-causing bacteria (like the strains of E. coli most frequently used in labs) die just as well as their infectious counterparts. colophon is 100% right: working with infectious bacteria - particularly in a non-lab setting! - could be dangerous to yourself and anyone you come in contact with, and is probably considered illegal. If you don't have a way to be sure of what strains you're working with (and isolating bacterial strains is hard!), any bacteria you're growing might be dangerous.

If you want to gather actual data, consider asking local schools, universities, hospitals, labs, etc. for help. Though they may rarer, or more strapped for resources, these institutions still exist in third-world countries - particularly if you're somewhere where you've got access to the internet! If you're interested in doing this out of personal curiousity or to teach children about antibiotics/bacteria/science, I suspect they would be more than willing to help - and that they will be able to point you towards books (biology texts) that will help you understand more about what you want to do and about how bacteria work. (Forgive me if it's a matter of English fluency, but it doesn't sound like you know much about bacteria, antibiotics, etc.)

If you're just trying to do a one-off demonstration of antibiotic efficacy (i.e., something along these lines) as opposed to an organized set of consecutive experiments, the risk is less: swab mouth-bacteria on an agar plate, put antibiotic-soaked paper discs on the plate, close the lid, observe for a day or few, and don't open it until you're ready to dump it in a vat of bleach. This sort of demonstration is relatively safe and is done by homeschooling parents and high school everywhere. However, this sort of basic demonstration is useless for gathering of actual, consistent, useful data for all the reasons everyone else has outlined.

Again, if you want to do anything more, any kind of extended experimentation, any kind of attempt to get real and consistent data, you do not at this point want (or need) a home lab. You need to learn more about what you're doing, both theoretically and practically before you can even consider figuring out whether it is possible to make a safe home lab in your situation.
posted by ubersturm at 1:27 PM on January 25

What colophon said is correct with regards to testing the minimum inhibitory concentration of some given agent, but that assumes you can actually culture the bacteria in question on whatever you're using to make your plate media. Step one would be figuring out a good growth media and then getting it sterile.
posted by rxrfrx at 4:16 PM on January 25

Yeah, I'd have to say that this is potentially a very bad idea. If you're just looking for answers for a particular substance you can do literature searches via Pubmed. This is an index of published scientific material. If you're wanting to do it as an experience thing then I suggest taking courses at a community college (or something equivalent) in either microbiology or in general laboratory techniques. Biochemsitry (which is what I do), is more concerned with the nitty gritty of the inside of the bacteria (or cell) and less the with the general response to the drug (ie live or die). I would only take biochem if you wanted to know why a bacteria was resistant to the compound of interest. Happy Learning and feel free to MeFi mail me if you have more questions.
posted by LunaticFringe at 6:39 PM on January 25