In a study of lipopolysaccharide synthesis, which organism is most likely to test positive for genes involved in lipid A biosynthesis?

• A. Candida albicans
• B. Clostridium difficile
• C. Mycoplasma pneumoniae
• D. Pasteurella multocida

Answer: (D)

Lipid A is a component of lipopolysaccharides (LPS), which are found in the outer membrane of Gram-negative bacteria. The presence of genes involved in lipid A biosynthesis is characteristic of organisms that possess an LPS layer.

Pasteurella multocida is a Gram-negative bacterium, and it is well known for containing lipopolysaccharides in its structure. The genes responsible for the synthesis of lipid A are crucial for its role in the overall biosynthetic pathway of LPS. This characteristic makes Pasteurella multocida the most likely organism to test positive for genes involved in lipid A biosynthesis among the options provided.

In contrast, Candida albicans is a yeast and does not have a typical Gram-negative cell wall structure or LPS. Clostridium difficile is a Gram-positive bacterium and therefore does not produce lipopolysaccharides containing lipid A. Mycoplasma pneumoniae lacks a cell wall and thus does not synthesize lipid A or possess LPS, as these structures are typical of Gram-negative bacteria.

Thus, Pasteurella multocida is correctly identified as the organism most likely to test positive for genes involved in lipid A biosynthesis due to its classification as a Gram-negative bacter