CM Colony Morphology
Learning Objectives
The student will
Follow oral and written instructions and manage time in the lab efficiently.
Apply correct terminology regarding microbial growth, when making observations.
Background/Theory
On agar plates, bacteria grow in collections of cells called colonies. Each colony arises from a
single bacterium or a few bacteria (CFU). Although individual cells are too small to be viewed with the
unaided eye, masses of cells can be observed. Colonies can have different forms, margins, elevations
and colors. Observing colony characteristics is one piece of information that microbiologists can use to
identify unknown bacteria. (Petersen, 2016)
In this exercise you will be drawing colonies and describing each type’s size, shape, elevation,
margin, color and texture. Keep in mind that the colony characteristics of a microbe may change
depending on the medium, time and temperature of incubation. The medium supplies the nutrients and
other materials for the cell to use. Along with the size of individual cells, the colony size depends on the
speed at which the cells divide. This is determined by the organism’s inherent cell cycle, the availability
of nutrients and the organism’s optimal growth temperature.
Size can be actually measured in millimeters or described as “pin point.”
Colony form means the shape and can be circular, irregular, or rhizoid (branched). This is the
cumulative (macroscopic) effect of the microscopic cellular shape and arrangement.
Elevation refers to the cross sectional view or profile of the colony. It can be raised, flat,
convex, concave or umbonate.
Figure 1 Colony Forms
