Lab #4: 2-2

What is a bacterial colony?

A visible mass of cells produced when a bacterial cell divides repeatedly on a suitable solid nutrient medium.

What factors influence colony morphology?

Genetics, nutrient availability, temperature, and incubation time.

What are the 7 basic categories of colony morphology?

Size, shape, margin, surface, elevation, texture, and optical properties.

How is colony size described?

By measuring its dimensions—diameter for circular colonies or length and width for other shapes.

What are common colony shapes?

Round (circular), irregular, and punctiform (tiny/pinpoint).

What are common colony margins?

Entire (smooth), undulate (wavy), lobate (lobed), filamentous (unbranched strands), and rhizoid (branched/root-like).

What are common colony surface characteristics?

Smooth, rough, wrinkled (rugose), shiny, or dull.

What are common colony textures?

Moist, mucoid (sticky), butyrous (buttery), or dry.

What are common colony elevations?

Flat, raised, convex, pulvinate (very convex), and umbonate (raised in the center).

What optical properties can be used to describe colonies?

Opaque or translucent.

What does opaque mean?

You cannot see through the colony.

What does translucent mean?

Light passes through the colony.

How should colony shape, margin, surface, texture, and color be observed?

From above with the plate level, using reflected light.

How should colony elevation be observed?

Tilt the plate slightly at eye level.

How should opacity and translucence be observed?

Using transmitted light, such as placing the plate on a colony counter or illuminating it from behind.

How should colony dimensions be measured?

From the base of the plate rather than through the lid.

What should be included when reporting colony morphology?

The colony's morphology, color, size, medium, incubation time, and incubation temperature.

Why is colony morphology useful in microbiology?

It helps distinguish microorganisms and is often an early indication that one organism differs from another.

If two colonies look different under the same growth conditions, what does this suggest?

They are most likely different species.

Does having identical colony morphology prove two colonies are the same species?

No. Different species can produce virtually identical colonies.

What is a colony counter useful for?

Magnifying colonies so subtle differences in shape and size can be observed.

What type of light is best for observing colony color and many other features?

Reflected light.

What is the grid on a colony counter used for?

Counting and measuring colonies; each large square represents 1 cm².

What should you do if you see a distinctive colony feature that has no established name?

Create a descriptive name that others can easily understand.

Why should plates with BSL-2 organisms or fuzzy growth not be opened?

BSL-2 organisms may be hazardous, and fuzzy growth may indicate fungi whose spores can spread and contaminate the laboratory.

What should you do if you are unsure whether a plate is safe to open?

Ask the instructor.

What is a mucoid colony?

A colony with a sticky texture.

What is a butyrous colony?

A colony with a buttery consistency.

What is a rugose colony?

A colony with a wrinkled surface.

What is an umbonate colony?

A colony that is raised in the center.

What is a pulvinate colony?

A very convex colony.

What is a punctiform colony?

A tiny, pinpoint colony.

What is a rhizoid colony margin?

A branched margin resembling roots.

What is a filamentous colony margin?

A margin consisting of unbranched strands.

What is the main purpose of Exercise 2-2?

To examine and describe the colony characteristics of bacteria growing on agar plates using standard colony morphology terminology.