Which statement correctly describes Gram-negative bacteria?

Which statement correctly describes Gram-negative bacteria?

• A. Stain blue due to a thick peptidoglycan layer
• B. Lack lipid content
• C. Stain red due to a thin cell wall with high lipid content
• D. Are never pathogenic

Answer: (C)

Gram-negative bacteria are identified by a thin peptidoglycan layer and an outer lipid-rich membrane. This structure causes them not to retain the crystal violet-iodine complex after the alcohol decolorization step in Gram staining, so they take up the counterstain and appear red/pink. The presence of a high lipid content in the outer membrane is a key feature that facilitates this decolorization and the characteristic red staining. Therefore, the statement describing these bacteria as staining red due to a thin cell wall with high lipid content correctly captures what Gram staining reveals about their cell envelope. In contrast, a thick peptidoglycan layer would retain the violet stain (Gram-positive), lack of lipids is not true for Gram-negative bacteria, and Gram-negative organisms can be pathogenic, so they are not inherently nonpathogenic.

Gram-negative bacteria are identified by a thin peptidoglycan layer and an outer lipid-rich membrane. This structure causes them not to retain the crystal violet-iodine complex after the alcohol decolorization step in Gram staining, so they take up the counterstain and appear red/pink. The presence of a high lipid content in the outer membrane is a key feature that facilitates this decolorization and the characteristic red staining.

Therefore, the statement describing these bacteria as staining red due to a thin cell wall with high lipid content correctly captures what Gram staining reveals about their cell envelope. In contrast, a thick peptidoglycan layer would retain the violet stain (Gram-positive), lack of lipids is not true for Gram-negative bacteria, and Gram-negative organisms can be pathogenic, so they are not inherently nonpathogenic.