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NEED HELP ASAP with experiment on E. coli

Postby alexa6745 » Mon May 20, 2019 4:29 pm

Hey there! I’ll introduce myself and my situation. I am Alexa and I am a Freshman taking Honors Biology. Our class has to make an individual project from scratch coming up with a topic, doing your experiment after research and making a procedure, and making graphs (data analysis) plus making a one slide presentation with all the info and pictures of what your experiment is and the results. After thinking about what to do I decided to test; The Effects of Isopropyl Alcohol on E. coli (my title for my presentation. This is my procedure I have typed out on Google Docs:

For my procedure, I’ll start by taking 3 petri with LB agar in each of them, taking 10 µL of E. coli out of the container it comes in and place it in the center of each dish, then using an inoculating loop spread the E. coli around making sure to cover the whole petri dish. On another day, use one dish as the control, not putting any antiseptic in it. Put 50µL of 70% isopropyl alcohol in one petri dish, 50µL of 60% isopropyl alcohol in another, and 50 µL of 50% isopropyl alcohol in the last one. After one minute to let the E. coli to sit with the isopropyl alcohol, transfer the E. coli to two new Petri dishes, one for each trial, that is split into four quadrants for each concentration and the control. The only way to tell if the bacteria are dead would be to transfer them to a new Petri dish with nutrient agar and see if they will grow up again. Injured bacteria would take longer to recover and grow, so it would take a few days for them to grow, given that they won’t have enough time to do so only letting them grow for two days. Then on Monday, take a picture with a smartphone. Using the ImageJ software, determine how many colonies are in each petri dish.

It was going well at first, on Friday the 10th, I grew my bacteria, let them sit for a week and I came back and they were all in check ready to go. I used 8 petri dishes in total, one for the control then one 50%, 60%, 70% times two for a second trial. I went back on Friday the 17th (our days to work on our project in-class is every Friday), to add my isopropyl alcohol. I did that putting a drop onto a few colonies, waiting a minute or two, then using a disposable inoculating loop, transferred one colony to the new petri dish (as my teacher recommended only one colony). Over the weekend I used the software, ImageJ, to count the colonies from three pictures of the dishes before adding the isopropyl alcohol and put it in a data table. I checked back today, and what I saw was not what I was looking for. On each quadrant was a lawn of growth when only the control should have had any growth. I know that what I have done can’t be changed as the presentation is due at midnight on Wednesday the 29th of May, meaning I wouldn’t have enough time to redo everything or a different way of doing it. I plan to write my reasoning (almost like a lab report for our class) about how my data was inconclusive, which I am absolutely fine with since not every experiment works as planned, it’s apart of the learning process :D.

I have the data from before I added the isopropyl alcohol:

Before isopropyl alcohol
Colony Count
Trial 1
control- 105 counted e. coli colonies
50%- 128 counted e. coli colonies
60%- 113 counted e. coli colonies
70%- 109 counted e. coli colonies
Trial 2
control- 102 counted e. coli colonies
50%- 103 counted e. coli colonies
60%- 101 counted e. coli colonies
70%- 125 counted e. coli colonies

My main question would be, how would I put in data for my graph, it’s required, even though my bacteria ended up being a lawn of growth? Thanks in advance!! :D

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Re: NEED HELP ASAP with experiment on E. coli

Postby DrSullivan » Tue May 21, 2019 12:51 pm

Hi Alexa,

Sorry your experiment didn't work. Unfortunately, that's often how science works.

You could graph your data based on percent confluence. Confluence means the amount of the plate that is covered by the bacteria. You'd have to estimate how much of the plate is covered for your initial counts, but your end measure would be 100%. You could then graph them as overlapping xy curves, with each sample being it's own line connecting the two time-points.

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Re: NEED HELP ASAP with experiment on E. coli

Postby alexa6745 » Tue May 21, 2019 4:49 pm

Hi DrSullivan,

That sounds like a fantastic idea! If I think of another question I'll post it on this thread. Thank you so much for your help! :D

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