LAUSR

Abstract Aeromonas schubertii is associated with multi-organ necrosis disease that frequently infects cultured snakehead fish. We examined whether type IV pili were important in the pathogenicity of A. schubertii. A Tap pilus mutant (Δpili) was constructed by insertional mutagenesis of the tapM/N/O/P/Q gene cluster. Compared with the wild-type (WT) strain, the proliferation was not changed, but the sensitivity to oxidative stress and low pH were different. The mutant displayed increased survival within macrophages compared with the WT strain. In contrast, cell and tissue adhesion of the mutant was significantly lower than the WT strain. Fish challenged by immersion resulted in reduced cumulative mortality of the mutant compared with the WT strain although intraperitoneal infection was identical for both strains. Expression of IFN-γ, IL-1, TCR, CC22, CD4 and CD40 in infected fish were similar between the two bacterial strains. Together these data indicated that tapM/N/O/P/Q is necessary for Tap pilus biogenesis in A. schubertii and adhesion is a key function for pathogenicity that is mediated by Tap pili.