Catalase is a critical virulence factor in Aeromonas schubertii infection of snakehead fish (Channa argus).

Aeromonas schubertii is an emerging fish pathogen that causes visceral nodules and high mortality in snakehead (Channa argus), but the molecular basis of its virulence remains poorly understood. Catalase detoxifies host-derived hydrogen peroxide and may be critical for pathogenesis. In this study, we constructed an isogenic catalase-deficient mutant (Δcat) of A. schubertii and its complemented strain (C-cat) to evaluate the contribution of catalase to pathogenesis. The results showed that deletion of catalase did not affect growth or colony morphology but significantly reduced catalase activity, decreased hydrogen-peroxide tolerance more than 100-fold, and impaired survival at mildly acidic pH 6. In RAW264.7 macrophages, Δcat showed more than twofold lower intracellular survival after 6h, but this effect was partially mitigated in C-cat. During immersion challenge of juvenile snakehead, cumulative mortalities at 14 days were 100% for wild-type A. schubertii, 0% for Δcat, and 50% for C-cat. These findings demonstrated that catalase-mediated catalase activity was indispensable for oxidative stress resistance, intracellular persistence, and full virulence of A. schubertii, and highlighted catalase as a potential prophylactic target in aquaculture disease control.