Counting colonies is traditionally
performed manually using a pencil and a click-counter. This is generally a
straightforward task, but can become very laborious and time consuming when
many plates have to be enumerated.
Alternatively semi-automatic (software)
and automatic (hardware + software) solutions can be used.
Colonies can be enumerated from
pictures of plates using software tools. The experimenters would generally take
a picture of each plate they need to count and then analyze all the pictures
(this can be done with a simple digital camera or even a webcam). Since it
takes less than 10 seconds to take a single picture, as opposed to several
minutes to count CFU manually, this approach generally saves a lot of time. In
addition, it is more objective and allows extraction of other variables such as
the size and color of the colonies.