How does the agar concentration in media used for motility testing differ from that used for standard plate cultures?

• A. Motility testing media does not contain any agar.
• B. Both motility testing and plate culture media use the same agar concentration.
• C. Motility testing media contains a lower concentration of agar to allow bacteria to move through it.
• D. Motility testing media contains a higher concentration of agar to restrict bacterial movement.

Answer: (C)

Verified step by step guidance

1. Understand the purpose of agar concentration in microbiological media: Agar is a solidifying agent that provides a semi-solid or solid surface for bacterial growth.
2. Recognize that standard plate cultures use a higher agar concentration (usually around 1.5%) to create a firm surface where bacteria grow as isolated colonies without movement through the medium.
3. Know that motility testing media requires a lower agar concentration (typically around 0.4%) to create a semi-solid medium that is soft enough to allow motile bacteria to move or swim through it.
4. Compare the agar concentrations: lower agar concentration in motility media facilitates bacterial movement, whereas higher agar concentration in standard plates restricts movement and supports colony formation.
5. Conclude that motility testing media contains a lower concentration of agar than standard plate cultures to allow bacteria to move through the medium, which is essential for observing motility.