[bbkevin817]

Hi, I'm doing a science fair project and it involves growing bacteria (E. coli) and determining the effectiveness of garlic in fighting bacteria. The link is here: http://www.all-scien...t1098_39_1.html

I have a couple questions about this project...
1) How long would it take me to grow the E. coli without an incubator? I have an empty oven that (I think) maintains a constant temperature, and I have a heating pad; would I be able to use any of those as an "incubator?"
2) Why is it necessary to add the E. coli specimen to milk before putting it on the agar petri dish?

Also, this is irrelevant, but in case the topic above does not work out, I might do a project requiring ampicillin. If I end up doing that project, how will I acquire the ampicillin? Isn't a prescription from a doctor required for apicillin?

Thanks.

[Horza2002]

Ampicillin is an antibiotic so you won't be able to get hold of it unless you have a perscription. And using ampicillin only works if you've made the mutant that contains the ampicillin resistance cassette inserted...otherwise it will kill the E. coli too.

E.coli grow very quickyl at 37oC, dividing once every 30mins or so. However, if your not growing them at thi stemperature it will be slower thn that...it all depends on how much you want really

[Vulgaris]

The E. coli will grow up over night if you just leave it at room temperature. It definately grows faster at 37 degrees, but lower temperatures will also do if the medium contains all the important nutrients. If you use a heating pad, make sure it doesn't get too hot! Probably the reason you are asked to mix it with milk is that the milk will act like a simple medium for a preincubation, as E. coli is able to degrade lactose under anaerobic conditions. Making a suspension of the E.coli cells will make it easier to plate them out evenly on the solid medium.

/Vulg

[CharonY]

On plates and on the table it may take 1-2 days, especially in presence of ABs (even when resistant). Depends a bit on how fresh and viable the starting culture. Sometimes can even take up to three days to get a decent lawn (everything in full medium). For heating avoid temperatures over 38-39 degrees. If you cannot gurantee that keeping it at room temperature is definitely preferable.

I suspect that mixing it with milk is just an easy way to avoid using buffer or media for plating. It depends on what culture you have. If you start from a plate and want to make a lawn you would have take off cells and resuspend it in buffer or media. I suppose milk could work as a cheap alternative. If you already got a liquid culture you often have to dilute it to a specified cell density (so that your experiments have all the same start conditions). Again, this is usually done with media or buffer.

To get ABs you definitely have to ask your school whether they have/require a permit to get it from chemical suppliers.

This post has been edited by CharonY: 20 July 2011 - 10:11 PM

[ewmon]

Here's a general idea of what to expect (it's the only such graph I could find).

X axis. The temperatures in Celsius are shown on the graph next to their points on the line (so forget about the confusing x axis).

Y axis. The y axis is also not obvious to the uninitiated. It shows the number of doublings per hour. So the "2" means that it doubles twice an hour --- aka every thirty minutes. Conversely, the 0.5 means that it's only halfway toward doubling in an hour --- aka it takes two hours for the bacteria to double.

As CharonY indicated, try to stay away from temps greater than 37°C. The higher temperature range (>37°C) has a much sharper slope as compared to the lower temperature range (<37°C), probably because higher temps distorts the proteins in the bacteria (and then the proteins can't do their job).

The concern is that you want to minimize the other factors affecting the growth rate among your plates, and you're almost guaranteed that the temperature among the plates will vary, perhaps by several degrees. So, you'd want to incubate them within a range of temps that's flattest, and that would be low temp range. The 39°C point is the flattest, of course, but your probably could not keep all plates within one degree of it.

I recommend using the heating pad under the plates with a clear bowl-like covering over them --- basically an incubator. As for accurately monitoring the temp, you might want to use a clinical thermometer (the ones that go under the tongue, or wherever), but they probably don't have a large lower temp range because they're mostly used to indicate a fever. Yet, a regular room/outdoors thermometer might not be accurate enough.

Okay, the lecture is over.

This post has been edited by ewmon: 20 July 2011 - 11:06 PM