Which Gram-positive bacterium is known to have lipopolysaccharide (LPS)?

The correct answer is Listeria monocytogenes. This bacterium, while primarily classified as Gram-positive due to its thick peptidoglycan layer, has unique structural features that include the presence of lipopolysaccharide (LPS) components. The LPS in Listeria is not as prominent or structurally typical as that found in Gram-negative bacteria, but it is still an important characteristic of its cell envelope.

Listeria monocytogenes is notable in various ways, including its ability to cause foodborne infections and its intracellular lifestyle, which facilitates immune evasion. This duality of being Gram-positive yet harboring LPS elements highlights the complexity of bacterial classification and cell wall composition.

In contrast, the other bacteria listed, such as Staphylococcus aureus, Bacillus subtilis, and Streptococcus pneumoniae, are firmly classified as Gram-positive and lack the LPS characteristic typical of Gram-negative bacteria. These organisms possess a different type of cell wall structure that does not include the lipid A component found in LPS, which is critical for understanding the distinctions in immune responses elicited by various bacteria.