Bacterial Colony | Morphology, Characteristics & Examples

Haripriya Munipalli, Angela Hartsock
  • Author
    Haripriya Munipalli

    Haripriya Munipalli has taught botany and biochemistry to undergraduates for 7 years. She has M.Sc. in Plant Sciences degree from University of Hyderabad, India and Master of Philosophy degree from Annamalai University.

  • Instructor
    Angela Hartsock

    Angela has taught college microbiology and anatomy & physiology, has a doctoral degree in microbiology, and has worked as a post-doctoral research scholar for Pittsburgh’s National Energy Technology Laboratory.

What is a bacterial colony? Learn about colony morphology and colony characteristics of bacteria. See the definition of a bacterial colony and colony morphology examples. Updated: 10/19/2021

Table of Contents


What is a Bacterial Colony?

Bacteria grow on nutrient mediums as colonies. The bacterial inoculum consisting of a few bacteria is made to grow on the medium to form bacterial colonies. A group of microorganisms originates from a single mother cell. So, a colony of bacteria comprises a clone that is genetically alike. High-resolution imaging tools and biophysical characterization techniques have only recently improved the learning process of bacterial colony growth, as well as the growth of diverse colony sizes at the microscopic and molecular levels. In unfavorable settings that simulate feeding conditions, bacteria's immobility inhibits their development in comparison to planktonic growth, and bacteria's response to environmental stress becomes more intense. The distribution of bacterial colonies at a distance and the size of the colonies are seen as a function of the initial population. Research has shown that there is a threshold between microcolonies (radius <100-200 micrometers) and macro-colonies (radius >200 micrometers). The growth of microcolonies resembled planktonic growth and pH gradients were observed. The growth of microcolonies is slower than the planktonic growth and pH micro-gradients were observed to be present around them because of limitations in diffusion that might occur outside as well as inside the macro-colonies.

The bacteria that are in food products are immobilized whether they are added as inoculum or those that are present naturally. Bacterial colonies are the visible accumulations of many bacterial cells. They grow as colonies either on the surface or within the food while they interact with the micro-environment. The bacterial colony cells absorb nutrients from the surrounding food and return some end products to the surrounding region modifying the micro-environment.

It's difficult to find data on the development and metabolism of bacteria in colonies. The growth and metabolism of bacteria in food are investigated in broth media with planktonic cultures. From the initial studies, it has been observed that the growth of bacteria in the colonies occurs in a concentric pattern. The number of cells dividing reaches the exponential growth phase which is linearly associated with the Log of colony volume for colonies immersed or to the Log of colony area for surface colonies.

The study of bacterial colonies does occur. An investigation was done on the pathogenic bacterial colonies that were grown in agar or gelatin, and microelectrodes were used to measure the pH.

  • High-resolution imaging techniques (HRITs) were helpful in exploring small colonies (<100micrometers) and in measuring the pH to the resolution of a few micrometers. HRITs were also useful in increasing the monitored parameter numbers such as variability of shape and of growth, and variability of single-cell and of metabolism.
  • The molecular techniques used to study the difference between gene expression and protein expression were used to compare the planktonic growth to immobilized bacterial growth.
  • The carbon metabolism at various inoculation levels was studied by microcalorimetry.
  • Imaging fluorescent techniques have helped in the observation of colonies in an opaque matrix-like model cheese.

The studies on bacterial colony growth showed that the growth of colonies was determined by the local concentration of substrates and by the possible limitations of substrate diffusion or end-products in solids.

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Colony Morphology

What is colony morphology?

Colony morphology is one of the cultural characteristics of a bacterial colony that is visible on an agar plate. Identifying the bacterial colony morphology is a vital skill that is used in the microbiology lab to recognize microorganisms from their variety. A colony must be isolated from other colonies to identify its shape, size, color, texture, and surface appearance. Another vital colony characteristic of the bacteria is hemolysis. Hemolysis is the destruction of blood cells that are components of blood agar.

Circular, Entire, and Black colony

Circular, Entire, and Black

Bacterial colony morphology chart

Bacterial Colony Morphology

Bacterial Colony Morphology

Colony Characteristics of Bacteria

An organism that grows in or on the media is focused more on the identification of bacteria and fungi. This identification will aid in gathering the colony characteristics of bacteria on agar plates described as colony morphology. Initially, looking at the colony morphology may not appear to be very useful. But morphology is important in identifying a bacterium. The bacterial colony characteristics can be identified based on the features of the colonies. Various bacterial species can produce various colonies. Clusters of bacteria form bacterial colonies. Bacterial colonies are not well-defined when compared to biofilms.

Bacterial colonies are groups of cells belonging to a clone grown either on the surface of the gel-type solid or embedded in it to absorb the nutrients from it. A bacterial colony is limited by size and it displays a maximum radius that ranges between a micrometer and a millimeter.


The size of the bacterial colony ranges from smaller to larger. Bacterial colony size is measured in millimeters. Small-sized colonies are less than 1 mm in diameter, medium-sized colonies are nearly 1 mm in diameter, and large-sized colonies are greater than 1 mm in diameter. The pinpoint-sized colonies are less than 0.5 mm in diameter.

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Frequently Asked Questions

What is the difference between a bacterial cell and a bacterial colony?

A bacterial colony is a mass of bacterial cells that have grown from a single mother cell on a solid agar medium. Binary fission gives rise to many bacteria. A bacterial colony consists of genetically identical bacterial cells.

What is an example of colony morphology?

Colony morphology is useful in identifying the type of bacteria. Bacterial colonies are classified based on their form, margin, and elevation. Based on their form, bacterial colonies are referred to as circular, irregular, filamentous, and rhizoid. Based on their elevation, they are classified as raised, convex, flat, umbonate, and crateriform. Based on their margin colonies are classified as entire, undulate, filiform, lobate, and curled.

What are the types of bacterial colonies?

Some colonies based on their form are filamentous and circular. Tiny colonies are referred to as punctiform colonies. Based on the side view of the colony, it is elevated. The magnified shape of the edge of the colony indicates the margin or border of the colony. Based on the surface of the colony, it is smooth, rough, wrinkled, glistened, and dull. Based on the opacity of the colony, bacterial colonies are transparent, opaque, translucent, and so on, Colonies appear in purple, white, red, and buff colors.

How is a bacterial colony formed?

When the bacterial cell is grown in the medium with necessary nutrients, the cell grows and develops into groups of bacteria called bacterial colonies. Based on the type of bacterial cell, the morphology of the colony differs. Many thousands, millions, and billions of cells are piled up to become visible to the naked eye in the colony.

How do you identify a bacterial colony?

A bacterial colony can be identified by the morphology of the colony. Different types of bacteria give rise to colonies that look different. Some of the bacterial colonies are colored, some are circular in shape, and a few others are irregular. The shape, size, and pigmentation of the colonies are the characteristics that determine colony morphology.

What is a bacterial colony?

A bacterial colony is a mass of bacterial cells that have arisen from a single mother cell. A single mother cell reproduces to create a group of genetically identical cells to form a colony with different morphology depending on the type of bacteria.

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