Listeria monocytogenes Has Both Cytochrome -Type and Cytochrome -Type Terminal Oxidases, Which Allow Growth at Different Oxygen Levels, and Both Are Important in Infection.

is a foodborne pathogen responsible for a number of life-threatening infections of humans. During an infection, it invades epithelial cells before spreading from the intestine to the cells of the liver and spleen. This requires an ability to adapt to varying oxygen levels. Here, we demonstrate that has two terminal oxidases, a cytochrome -type (CydAB) and a cytochrome -type menaquinol (QoxAB) oxidase, and that both are used for respiration under different oxygen tensions. Furthermore, we show that possession of both terminal oxidases is important in infection. In air, the CydAB -type oxidase is essential for aerobic respiration and intracellular replication, and mutants are highly attenuated in mice. In contrast, the QoxAB -type oxidase is required neither for aerobic respiration in air nor for intracellular growth. However, the mutants are attenuated in mice, with a delay in the onset of disease signs and with increased survival time, indicating a role for the QoxAB -type oxidase in the initial stages of infection. Growth of bacteria under defined oxygen conditions revealed that at 1% (vol/vol), both oxidases are functional, and the presence of either is sufficient for aerobic respiration and intracellular replication. However, at 0.2% (vol/vol), both oxidases are necessary for maximum growth. These findings are consistent with the ability of to switch between terminal oxidases under different oxygen conditions, providing exquisite adaptation to different conditions encountered within the infected host.