Gram Staining: Safranin and Outer Membrane

This question involves evaluating an assertion about Gram staining and a reason related to bacterial cell structure.

Assertion [a] Truthfulness

The assertion states that Gram-negative bacteria show staining with safranin. Safranin is the counterstain used in the Gram staining procedure. It stains Gram-negative bacteria pink or red after the decolorization step. Therefore, Assertion [a] is true.

Reason [r] Truthfulness

The reason states that Gram-negative bacteria possess an outer membrane containing lipopolysaccharides (LPS). This structural feature is characteristic of the cell wall of Gram-negative bacteria. Thus, Reason [r] is true.

Reason for Assertion

The Gram staining process differentiates bacteria based on their cell wall composition. Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane rich in lipopolysaccharides. During decolorization (e.g., with alcohol), the crystal violet-iodine complex is washed out more easily from Gram-negative cells due to the structure of their outer membrane. The subsequent application of safranin counterstains these decolorized cells pink/red. Therefore, the presence of the outer membrane with LPS is fundamental to why Gram-negative bacteria are decolorized and then stained by safranin. Reason [r] correctly explains Assertion [a].

Conclusion

Both the assertion and the reason are true, and the reason correctly explains the assertion.