Bacteria Science Fair Questions - A few basic and complex questions about bacteria (Nov/04/2005 )
There is a terminology problem here -- each tube is a culture; a culture is any volume of pure bacteria growing in media. You only need one tube of each organism. The question was what the volume of the culture is in each individual tube was (0.5 ml? 1 ml?), so we could guess whether there was enough liquid in a single tube for 15 Q-tips full.
It's not a problem to first streak the cultures to a plate and use that plate as an inocculum source for all the others after it has grown for a day.
Alright, I just tried calling, but they closed about 20minutes ago... However I'm wondering - if I buy just a commercial package of Q-tips, then open the box, are they steril enough to use without me sterilizing them myself? If not, how should I sterilize the Q-tips if I don't have an autoclave available to me?
Hi greatape 213,
Do you have any experience in working with bacteria?
It looks like you don´t have experience, if so, once again I strongly recommend you to do that with someone more experienced.
And don´t do that experience at home. If you don´t sterilize things well you might get a contamination problem.
Think twice
If you write your project and send it o a microbiology lab, with a letter of recommendation from your teacher my guess is that you will find a place.
What you need to use is not expensive for a lab but for you not only is expensive as it can become risky.
Take care and Success
I agree with macedo -- do you have a science teacher working with you? If you contaminate your experiments, the results will be worthless. It does take a little experience to be able to work with bacteria without introducing contamination.
In any event, a box of Q-tips will not be sterile, and are unsuitable to use. You can buy sterile cotton swaps at a drugstore, probably in the first aid section.
If you're talking to someone at the local hospital, they definitely have sterile cotton swabs -- maybe they could give you a handful (they probably come in a paper envelope, two to a pack). While you're talking to them, you should ask them if they have some sterile filter paper circles as well -- the clinical lab department wil likely have them, too, and would perhaps be willing to give you some.
Also, I'd just lke to point out that your statement "...while the bacteria are growing, and see if they spread away from the centerpiece. The more effective the antibacterial/disinfectant is, the further the bacteria will back away..." is incorrect.
The clear zone that appears around the chemical in question is due to the action of the chemical on the bacteria near it -- it either kills them (a bactericidal chemical) or stops them from growing (a bacteriostatic chemical). As the chemical on the plate diffuses out into the media, a concentration gradient is formed -- as the circle of diffussion gets wider, the concentration of chemical at the edge of the circle decreases. Thus, a very effective agent (one that is bactericidal or bacteriostatic at very low concentrations) will produce a larger circle of clearing than will one that only acts effectively at relatively higher concentraions.
It just came to me - could I say what I said earlier "while the bacteria are growing, and see if they spread away from the centerpiece. The more effective the antibacterial/disinfectant is, the further the bacteria will back away", if I used only bacteriostatic chemicals or only bactericidal chemical for my project, that way they would effect the bacteria in the same way?
The bacteria do not move. They exist on the plate where they are -- it is the chemical that moves (diffuses) out into the plate equally in all directions (thus forming a circle). As the chemical comes into contact with the bacteria that exist at that point on the plate, it kills them, or stops them from growing. Elsewhere on the plate, right up to the margin that defines the minimal concentration of chemical that has this effect, the bacteria grow normally, and produce a lawn. Where there is bacterial growth, there is a lawn and you can't see through it. Where the chemical has killed the bacteria or stopped their growth, there is no growth, and thus no lawn, and this area remains clear.
The concentration of the chemical is greatest near the circle of paper from which it diffuses, and decreases as the circle grows wider. Thus, a large zone of clearing indicates that the chemical remains effective at low concentrations.
The visual effect of a bacteriolytic chemical versus a bacteriostatic chemical is the same, as no growth due to the bacteria being stopped from dividing and no growth due to the bacteria being dead is the same -- no lawn in a ring around the paper from which the chemical diffuses.
I've found in many sources that some types of E. coli can be harmful and dangerous, and can cause disease. How can I make sure that the E. coli I will be growing won't have any of these harmful E. coli (0157:H7) in my culture?
Could I possibly do this experiment by myself if under the hospital's supervision, even if they aren't watching me all the time, just nearby? I haven't gotten a direct answer from the hospital if I can use their facilities yet, but I may find out tomorrow.
The concentration of the chemical is greatest near the circle of paper from which it diffuses, and decreases as the circle grows wider. Thus, a large zone of clearing indicates that the chemical remains effective at low concentrations.
The visual effect of a bacteriolytic chemical versus a bacteriostatic chemical is the same, as no growth due to the bacteria being stopped from dividing and no growth due to the bacteria being dead is the same -- no lawn in a ring around the paper from which the chemical diffuses.
Okay, but a major question just came into my head, how will I measure the cleared zone?I know a ruler wouldn't be exact, but how about a micrometer? Which kind would work best? I know they are expensive, but do you think there are any local places that usually have them available for me to borrow? A hospital? Thanks
Could I possibly do this experiment by myself if under the hospital's supervision, even if they aren't watching me all the time, just nearby? I haven't gotten a direct answer from the hospital if I can use their facilities yet, but I may find out tomorrow.
The strain you are buying is perfectly safe -- that company exists to sell supplies to schools. They could not send you a strain that was not safe, it'd be illegal.
The cultures they send you are pure cultures -- every single bacteria in the culture is exactly the same (for all intents and purposes); they are all descendants the same (safe) cell. All the bacteria coming from that culture (the ones growing on your plates) will also all be exactly the same. There is no chance of one "becoming" an 0157:H7 strain, it cannot happen.
The reason we were suggesting that someone with experience handling bacteria help you is not because it's dangerous, but because it takes some experience to handle bacteria without introducing contaminaton, and a contaminant on your plates or in your cultures will ruin your experiment.
As far as measuring your zones goes, a millimeter ruler will be fine. This is more of a qualitative test than a quantitative one -- your measurements are only valid in comparison to one another. So, if you measure all your zones with the same ruler, and do them all the same way, you can compare them to one another, and a larger zone will indicate that whatever chemical produced it is more effective at stopping the growth of your bacteria than a chemical that produced a smaller zone against the same bacteria.
Excellent News! My teacher and I have contacted the local college, Bowdoin College, and someone working in the microbiology department there is willing to help and advise me! I will able to use their facilities to grow the bacteria and do all the testing there, so I'll get some experienced help with this.
Excellent news! This is a good experiment -- you'll learn a lot, and it's not too hard to do, if someone shows you the right way to do it. They could probably give you bacteria, plates, paper disks, and swabs as well, so you don't have to spend any money (I know I would, if you were a little further south -- I'm in Massachusetts).