See all Posts
Image of bacteria colony on agar plate for an article about what a colony is in microbiology.
Published On: November 3rd, 2020

Microbiology is the study of microorganisms, including bacteria, fungi, viruses, protozoa, and more. It includes research on the physiology, cell biology, and biochemistry of the microorganisms—an essential part of this research process requires growing and harvesting microbial colonies.

A further definition of a colony in microbiology and the processes involved in working with it follow.

What is a “Colony” in Microbiology?: An Overview

In microbiology, a “colony” is a group of bacteria, fungi, and other microorganisms grown on a solid agar medium. The cells plated on this medium grow to form a mass, which can then be duplicated for further use in the lab.

Colony morphology is used to pick out a pure colony—that is a colony grown from a single parent cell. Morphology encompasses physical characteristics like form, margin shape, elevation, surface texture, opacity, and color.

Observing the colony morphology can be done with the naked eye, or it can be imaged with a camera and image analysis software for automation.

Working with Bacterial Colonies in The Lab

Microbial colonies are widely used in a wide range of research and to produce various proteins and enzymes. Below are the significant ways that labs work with microbial colonies.

Culturing Colonies on Agar

The purpose of culturing microorganisms, often bacteria on agar, is to isolate the bacteria’s pure strain for further use. The most common method is the “streak plate” method. It essentially dilutes the concentration of bacteria from the initial culture to form unique colonies from single cells.

In the streaking method, a sterile inoculation loop or swab is used to obtain a microbial culture is then spread over an agar surface. The bacteria are first streaked onto a section of the agar. Then, the loop is sterilized with heat to reduce the number of bacteria on it and the streaking is repeated to spread the bacteria to another section of the agar.

The sterilization and streaking is repeated until it sufficiently covers the agar medium. After incubating the bacteria to allow visible colonies to grow from the single-cell sources on the agar, you can pick the colonies from the agar plate for use in other processes manually by hand or with a colony picking robot.

How to Count a Colony of Bacteria on a Petri Dish

Counting bacteria in a colony is vital in research and the production of various products. By measuring the growth of bacteria and other microorganisms, researchers can estimate the strength of bacterial infections and monitor the fermentation progress.

A suitable bacterial colony is identified and picked up with a loop, pipette tip, or toothpick and then inoculated into growth media to count bacteria.

Alternatively, an automated colony picker can be used. The sample is then incubated overnight. Next, the cultured sample is diluted by a factor of 10 by adding and the dilutions are repeated five more times to acquire six samples with a dilution of 10-1 to 10-6.

Each of the dilutions are individually plated on a petri dish and incubated. After incubation, plates containing 30 to 300 distinct, separate colonies are selected, and the colonies on it are counted.

Lastly, to obtain the total viable cell count, the number of colonies is multiplied by the sample’s dilution factor on the chosen agar medium.

By knowing what a colony is in microbiology and how to culture and count it, you can have a better understanding of the processes involved in using microbial colonies in research.

Instruments like a colony picking robot, which can often pick over 2500 colonies per hour, can help you speed up workflows in the lab, increase efficiency, and reduce errors.

To learn more about how automated colony pickers can help your lab improve productivity, contact Hudson Robotics.