Listeria monocytogenes is a Gram-positive facultative anaerobe and an excellent model pathogen for investigating regulatory changes that occur during infection of a mammalian host. SpxA1 is a widely conserved transcriptional regulator that induces expression of peroxide-detoxifying genes in L. monocytogenes and is thus required for aerobic growth. SpxA1 is also required for L. monocytogenes virulence, although the SpxA1-dependent genes important in this context remain to be identified. Here, we sought to investigate the role of SpxA1 in a tissue culture model of infection and made the surprising discovery that Δ
