Which type of bacteria contains lipopolysaccharide (LPS) and porins?

• A. Gram-positive
• B. Gram-negative
• C. Gram-neutral
• D. Both

Answer: (B)

LPS and porins are located in the outer membrane of Gram-negative bacteria. The outer membrane is a distinct feature of these organisms, with lipopolysaccharide (LPS) spanning the outer leaflet and serving as a major endotoxin component, while porins form channels that allow small molecules to diffuse into the cell. Gram-positive bacteria, on the other hand, lack this outer membrane and instead have a thick peptidoglycan layer; they do not contain LPS or porins. The term Gram-neutral isn’t a standard classification, and calling it that would not fit the typical distinctions. Since only Gram-negative bacteria possess both an outer membrane with LPS and porins, they are the correct answer.