bacteria counting and identification

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bacteria counting and identification

Postby Dragon2014 » Sun Mar 30, 2014 4:50 pm

Hi Experts

I'm testing the quality of different brands ice cream.

1) is the dilution in water (bottle water) will be OK?
2) what it could be the good dilution to get a good bacteria count ? (e.g a 1g in 1 cup of water)
3) what could be an easy way to identify bacteria? e.g coli form bacteria

Thanks for your help
Dragon2014
 
Posts: 6
Joined: Mon Mar 17, 2014 1:13 pm
Occupation: student fifth grade
Project Question: Is there a way to count different types of bacteria in different samples of ice cream?
Project Due Date: April/07
Project Status: I am conducting my research

Re: bacteria counting and identification

Postby connief » Sun Mar 30, 2014 5:06 pm

Hello there,

It will be very helpful if you provide some more details about your question and experiment. For example, what is the main question you're testing? What is your hypothesis? What kind of experiment will you use to test your hypothesis? What do you mean specifically by the "quality" of the ice cream? How sterile it is? How delicious it is? How creamy it is? etc. Dilution in water should be okay (although if other experts have a better idea for a diluent to use, please share). It's difficult to tell what dilution to do to get a good count of bacteria because we don't know how much bacteria is actually present in ice cream in the first place, so I would do a range of dilutions, ranging from undiluted to a very dilute concentration. I would probably do a little research to see if people have identified the types of bacteria present in ice cream. First of all, this should give you an idea of whether or not you would even see anything on your agar plates--for example, if no bacteria are present in ice cream, you shouldn't be able to see anything. In addition, certain bacteria can only grow under certain environment conditions or on certain nutrients, so it would be nice if you have some sort of idea of the bacteria that will be present so you can grow them accordingly (i.e. Should you grow them in an aerobic or anaerobic environment? Should you let the plates incubate at 37 degrees C or room temp?, etc.). Bacteria typically form round colonies on the surface of agar plates. However, if you want to distinguish between different bacteria species by looking it at, that's a bit difficult because certain bacteria basically form similar sized colonies with similar colors/morphologies. Unless all of the different types of bacteria in your ice cream form colonies of distinct shapes/sizes/colors, it will be very difficult to tell which species is which without more sophisticated methods.

The following link is an experiment on the Science Buddies website which sounds pretty similar to what you want to do, except it's with yogurt instead of ice cream. http://www.sciencebuddies.org/science-f ... #procedure
You can adapt whatever procedures are appropriate for your experiment accordingly. :)

Let me know if you have anymore questions!

Best,
Connie
connief
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Re: bacteria counting and identification

Postby Dragon2014 » Sun Mar 30, 2014 5:39 pm

Hi there,

Thanks for your reply. Please find the following details for my science project

1. I am comparing different brands of ice cream to see which one has more bacteria.

2. If it's possible I want to identify CF bacteria in each brand and how to count them.

Thanks
Dragon2014
 
Posts: 6
Joined: Mon Mar 17, 2014 1:13 pm
Occupation: student fifth grade
Project Question: Is there a way to count different types of bacteria in different samples of ice cream?
Project Due Date: April/07
Project Status: I am conducting my research

Re: bacteria counting and identification

Postby connief » Sat Apr 05, 2014 4:24 pm

Hello there,

What do you mean by CF bacteria? Also, if you want to count bacteria, the best way to do it is to use a serial dilution approach, where you resuspend a defined amount of ice cream into a defined volume of diluent, and then do a series of dilutions and plate a certain volume of each dilution onto a separate plate. Since you don't know the exact concentration of bacteria that will be present in your ice cream, doing a series of dilutions will give you a good range over which you can get a countable amount of colonies on your plate. For example, if one of your plates is so full of bacteria that you can't distinguish between individual colonies, that dilution is way too concentrated and you wouldn't be able to count that accurately. However, if one of your plates only has 1 colony, that dilution is way too dilute to be an accurate representation of the actual numbers of bacteria. We usually try to count a dilution that will give us between 10-100 colonies, and then you can use that number and the fold-dilution you did to back calculate to figure out what the bacterial numbers in your original sample. Here is an excellent video that talks about serial dilutions: https://www.youtube.com/watch?v=pmRUBYlPMBM. And here's a site that goes into more detail of how to backcalculate: http://www.science-projects.com/serdil.htm.

Let us know if you have anymore questions!

Connie
connief
Expert
 
Posts: 249
Joined: Thu Apr 04, 2013 12:27 pm
Occupation: Graduate Student
Project Question: I am volunteering for the "Ask an Expert" program.
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