Select the most accurate statement.
a. The Gram stain is a simple stain.
b. Bacterial endospores appear green from the acid-fast stain.
c. The acid-fast stain is used to detect bacteria that have a capsule.
d. Bacterial flagella can only be seen with electron microscopes.
e. The mordant in the Gram stain is iodine.

Verified step by step guidance

1. Step 1: Understand the purpose of each staining technique mentioned. The Gram stain differentiates bacteria based on cell wall properties, the acid-fast stain identifies bacteria with waxy cell walls, and simple stains generally color all cells uniformly.
2. Step 2: Evaluate option (a): The Gram stain is not a simple stain; it is a differential stain because it distinguishes between Gram-positive and Gram-negative bacteria using multiple reagents.
3. Step 3: Evaluate option (b): Bacterial endospores are typically stained green by the endospore stain (using malachite green), not by the acid-fast stain, which targets mycolic acid in cell walls and stains acid-fast bacteria red.
4. Step 4: Evaluate option (c): The acid-fast stain is used to detect bacteria with mycolic acid in their cell walls (like Mycobacterium), not bacteria with capsules. Capsule staining is a different technique.
5. Step 5: Evaluate options (d) and (e): Flagella are very thin and generally require special staining or electron microscopy to be seen, so (d) is accurate. The mordant in the Gram stain is iodine, which helps fix the crystal violet dye, so (e) is also accurate. Compare these two to select the most accurate statement.

Key Concepts

Gram Stain and Mordant

The Gram stain is a differential staining technique that classifies bacteria as Gram-positive or Gram-negative based on cell wall properties. Iodine acts as the mordant, forming a complex with crystal violet dye to fix it inside the cell. This process is distinct from a simple stain, which uses only one dye without mordants.

Acid-Fast Stain and Its Targets

The acid-fast stain is used to identify bacteria with waxy, mycolic acid-rich cell walls, such as Mycobacterium species. It does not stain capsules or endospores. Endospores require a different staining method (e.g., malachite green stain), and acid-fast bacteria appear red, not green.

Microscopy of Bacterial Structures

Bacterial flagella are too thin to be seen with light microscopes and typically require special staining or electron microscopy for visualization. Electron microscopes provide the high resolution needed to observe fine structures like flagella, which are essential for bacterial motility.