4 replies to this topic

[ratanowski]

How do you could colonies that spread too quickly or irregularly? I have a poorly drawn picture I can try to explain. The colonies spread so rapidly and irregularly that I cannot get a good count. Even using serial dilutions I run into a problem where all of my dilutions with growth are large and spread and the next dilution there is no growth.

 

In the same vain, how do you count mold that has grown over the entire plate?

 

Any insight is greatly appreciated.

 

[ratanowski]

I attached an image but it is not showing up. I will try to link it here. 

[Alex V.]

could you outline your plating procedure?  is this a new problem or have you always had this issue?

[DS1]

Are you spread plating or pour plating?

 

For pour plating a good option is to pour about half of what you would normally pour, swirl, and set aside. After the agar has set and solidified, overlay with the other half. This will help with the surface spreading issue. For molds, it can be trickier. Some molds are much harder than others to count when they overgrow. Aspergillus takes practice but can be done. With other molds I will increase my dilutions until I get a countable range. If that doesn't work then try checking your plates everyday after 2-3 days and counting before the plate becomes overgrown.

 

For spread plating, you will either need to dilute or check your plates everyday to ensure they are not becoming covered before you get a count.

[ratanowski]

It is a pour plate method, standard pour plate but the issue is also that some colonies are large and connected, and I am often unsure of whether to count them as the same or different colonies. they  make like a wave pattern around the edge of the petri dish. I have not tried the double pouring agar method, but I will! Thanks to all for the advice.