Which statement correctly describes Gram-positive bacteria?

• A. Thick peptidoglycan layer; no outer membrane; stains purple; little periplasm; no LPS; contains teichoic acid
• B. Thin peptidoglycan layer; has outer membrane; stains pink; much periplasm; has LPS; lacks teichoic acid
• C. Thick peptidoglycan layer; has outer membrane; stains pink; little periplasm; has LPS; lacks teichoic acid
• D. Thin peptidoglycan layer; no outer membrane; stains purple; little periplasm; no LPS; contains teichoic acid

Answer: (A)

Gram-positive bacteria have a thick peptidoglycan cell wall and no outer membrane, which explains why they retain the crystal violet stain and appear purple. The thick wall traps the dye, and the absence of an outer membrane means there’s no outer-LPS barrier or significant outer envelope features. Teichoic acids are characteristic components of this wall, contributing to its structure and charge. The small periplasmic space and lack of LPS further distinguish Gram-positive envelopes. So, describing a thick peptidoglycan layer, no outer membrane, purple staining, little periplasm, no LPS, and the presence of teichoic acid lines up precisely with Gram-positive bacteria. If an outer membrane and LPS were present, or if the peptidoglycan were thin, the stain would typically appear pink, characteristic of Gram-negative bacteria.