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Questions about plate counting and plating technique ...


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#1 jeepgirl

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Posted 08 September 2004 - 07:45 AM

Okay, I'm using a range of 30-300 colonies for a plate to be considered countable. I'm plating in duplicate, then taking an average of the two for the colony count. Let's say I have a pair of plates where one falls in the range, while the other isn't in the range (either no growth, too few colonies, or too many), how would I go about averaging the two plates?

Also, I've always wondered about spread plates as opposed to pour plates, ie is there one type that is preferred over the other? In all of my undergrad labs, we went with spread plates, but I think this was probably more of a decision based on logistics then anything else. Now that I'm in my own lab, I find that pour plates are easier, mainly b/c I don't have to stress about having my "streak" plates turn into "smear" plates.

#2 jadefalcon

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Posted 08 September 2004 - 11:14 AM

we use spread plates all the time, even for diagnostic purposes - but it depends on the bug you want to count. some will only grow in poured plates, not on spreaded plates.

and we use three samples of each dillution, so when one plate drops out - which happens in research - you have two good ones left to take a mean value. if two or all three drop out, you have very bad luck - and - try it again!

mike
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#3 jeepgirl

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Posted 08 September 2004 - 11:41 AM

Jade,
Thanks for responding :D

So when it comes to spread plates vs pour plates, I should just go with whichever technique I feel more comfy?

#4 jadefalcon

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Posted 09 September 2004 - 03:26 AM

you should do what the special bug you investigate requires.

for most purposes we use spread plates, but when you get inconsitent results with one technique, you should try the other one and see if it works out better and then stick to the better technique.

mike
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