Calculating bacteria increase

[sciencefan]

Hello, I am looking for ways to calculate the bacterial increase. i performed my experiment and I tested the samples before and after. the baseline counts for my samples were:

Before after
1 -- 6 56
2 -- 9 122
3 --2 14

Is there a way to do calculation other than tell by how many colonies the sample increased. the judges said I was lacking math in my experiment. Thank you so much for any help you can advice.

[djschlesinger]

Hi sciencefan,

I think you are looking to calculate the growth "rate" of bacteria. This will allow you to determine the growth of a culture of bacterial cells over a given amount of time. Bacteria grow by cell division, meaning 1 bacterial cell splits into two bacterial cells, two bacterial cells split into four, and so on. This is called exponential growth. And under optimal laboratory conditions bacterial cells will double at regular intervals. For example, under optimal laboratory conditions, E. coli can double every 20 minutes or less. So, if you start with 1 E. coli cell and they double every 20 minutes, how many bacterial cells would you have in 1 hour? In order to represent exponential growth mathematically we have to talk about exponents (I will assume you are familiar with exponents). And when talking about teh doubling of a bacterial cell we express that as a power of two. Look at my example below:

2^0 = 1 bacterial cell
2^1 = 2 bacterial cells
2^2 = 4 bacterial cells
2^3 = 8 bacterial cells
2^4 = 16 bacterial cells

This sequence could go on forever, so an easy way to represent is as follows:

2^n, where n = the total number of cell divisions (or generations) that have taken place. If you know the generation time (how long it takes to double) of your bacterial cell then you can solve this simple equation. So, for the example above: if E. coli cells double every 20 minutes and there are 3 20-minute intervals in 1 hour, then n=3. Therefore, you have 2^3 = 8. So after 1 hour you would have 8 E. coli cells.

I hope this makes sense. Please let me know if need additional help.

Best of luck,
Dave

[sciencefan]

PLEASE HELP fast!!!!!
i need this by Friday please. I just read this in one of your experiment
Divide plate into 4 quadrants, and use the stereo microscope to count colonies in one quadrant. Multiply count by 4 to get total CFU/100 μL for the diluted sample. Then multiply by the total dilution factor to get CFU for each piece of pureed meat. You can then divide by the original weight of the meat to get CFU/g of meat.

Can you please guide me through it. If I have 73 CFU/ml colonies after defrosting my calculations will be like this. I am not sure fi I am doing it correctly.
Thank you.

73 times by 10 to the power of negative 3 = 0.073 CFU/per meat, then 0.073/45 grams will give me CFU per gram of meat???? Is that right? My numbers are too small. Does negative power change into positive?