Which deficiency causes failure of the neutrophil respiratory burst, leading to recurrent catalase-positive bacterial infections?

• A. NADPH oxidase
• B. Lactoferrin
• C. Superoxide dismutase
• D. Lysozyme

Answer: (A)

Neutrophils kill ingested microbes through a respiratory burst that starts with NADPH oxidase generating reactive oxygen species. This enzyme transfers electrons from NADPH to oxygen, creating superoxide, which is then transformed into hydrogen peroxide and other microbicidal species by subsequent enzymes such as myeloperoxidase. When NADPH oxidase is defective, this burst cannot occur, so neutrophils can’t effectively kill many ingested organisms. The infections that result are particularly associated with catalase-positive organisms because these pathogens break down their own hydrogen peroxide, removing a potential external ROS source the neutrophil could use to compensate for the defective burst. As a result, individuals become prone to recurrent infections with organisms like Staphylococcus aureus, Serratia, Nocardia, and Aspergillus.