MPO and infection: PMNs from individuals who lack a functional phagocyte oxidase or MPO fail to kill microbes normally.7 Specifically, patients with a defective NADPH oxidase develop chronic granulomatous disease (CGD), which leads to recurrent infections, predominantly by Nocardia, Aspergillus species, and catalase-positive bacteria including Staphylococcus aureus and Burkholderia cepacia.