How Do You Count Bacteria Colonies in a Petri Dish?

There are multiple ways to count the bacteria colonies growing in a Petri dish, from simple counting by hand, to complex machinery designed to electronically measure colony growth. Depending on how many Petri dishes need to be counted, and how often measurement is taking place, different users will benefit from different counting methods.

Counting by hand is appropriate for most lab settings, since the only resource required is time. It is both economical and easy; anyone capable of counting and recording spots observed in the Petri dish is capable of counting colonies via this method. There are some simple tools, including markers and counters operated by manual clicks, that can aid in the recording process. The downside of counting by hand is that it is time-consuming and can be prone to human error.

There are machines that have been designed specifically to measure the number of colonies present in a Petri dish. These machines provide users with an output that includes count numbers and growth over a specific period of time. Using counting machines is helpful in the lab environment where time is better spent in activities other than manually counting, and where accuracy is of extreme importance. The downsides of using counting machines include expense and potentially limited functionality of the device, beyond simple counting purposes.