Microbiology Exercise 11: Motility Agar and Flagella Staining

What is the purpose of the motility agar test?

To determine the motility of bacteria by observing growth patterns in the agar.

What does a positive result in a motility agar test indicate?

That motile bacteria can migrate away from the stab line, resulting in a red color throughout the agar.

What does a negative result in a motility agar test indicate?

That nonmotile bacteria will only grow along the stab line without spreading.

What are the key materials used in the motility agar test?

Motility agar tubes with tetrazolium salt, inoculating needle, and Bunsen burner.

What is the role of tetrazolium salt in the motility agar?

It is reduced to an insoluble red pigment, formazan, indicating bacterial growth.

What are the different types of flagellar arrangements?

Atrichous, peritrichous, lophotrichous, monotrichous, and amphitrichous.

What does 'atrichous' mean?

Bacteria without flagella.

What does 'peritrichous' mean?

Bacteria with flagella all around their surface.

What does 'lophotrichous' mean?

Bacteria with a tuft of flagella at one end or both ends.

What does 'monotrichous' mean?

Bacteria with a single flagellum.

What does 'amphitrichous' mean?

Bacteria with flagella at both ends.

What is the function of flagella in bacteria?

To enable movement in response to environmental cues.

What is positive phototaxis?

The movement of bacteria towards a light source.

What is negative phototaxis?

The movement of bacteria away from a bright light source.

How are flagella visualized in the laboratory?

Using flagella staining techniques and light microscopy.

What is a mordant in the context of flagella staining?

A substance that helps the stain adhere to the flagella, increasing contrast for visualization.

What is formazan?

An insoluble red pigment produced from the reduction of tetrazolium salt by growing bacteria.

What is the significance of observing motility in bacteria?

It helps in identifying bacterial species and understanding their behavior in different environments.

What is the incubation temperature for motility agar tests?

37°C for 24 to 48 hours.

What is the hanging drop technique?

A method for observing motility by placing a drop of culture on a slide and covering it with a coverslip.

What is the limit of resolution of a light microscope?

0.2 µm, which is insufficient to resolve bacterial flagella.

What happens to the color of the motility agar if bacteria are present?

The color changes to red in the areas where bacteria grow.

What is the purpose of sterilizing the inoculating needle?

To prevent contamination during the inoculation process.

What is the typical length and diameter of bacterial flagella?

Up to 20 µm in length and 0.05 µm in diameter.

What should be recorded after observing the motility agar results?

The distribution of growth in each motility agar culture.