The GspCD-dependent type II secretion system promotes necrotizing soft tissue infection caused by Aeromonas hydrophila.

Necrotizing soft tissue infections (NSTIs) are fulminant bacterial diseases characterized by rapid tissue destruction, systemic deterioration, and high mortality. Aeromonas hydrophila is an important causative agent of NSTIs, but the bacterial mechanisms that promote tissue destruction, in vivo expansion, dissemination, and host lethality remain incompletely understood. Here, we investigated the contribution of the GspCD-dependent type II secretion system (T2SS) to A. hydrophila virulence using transposon mutants, extracellular protein analyses, and a mouse NSTI model. Mutants carrying transposon insertions in gspD and gspC showed defective secretion of a FLAG-tagged truncated AerA construct and markedly reduced hemolytic activity in culture supernatants. Comparative analysis of extracellular proteins further showed that disruption of gspC reduced the abundance of multiple known or predicted virulence-associated extracellular factors, including AerA, Ahh, lipase, and metalloprotease. In the mouse NSTI model, both mutants exhibited attenuated virulence, including reduced serum markers of tissue injury, less severe histopathological damage, impaired in vivo expansion and dissemination, and decreased lethality. Together, these findings show that the GspCD-dependent T2SS plays an important role in A. hydrophila NSTI pathogenesis by promoting extracellular protein secretion, tissue destruction, bacterial spread, and host mortality.