Abstract
Aeromonas dhakensis is an emerging pathogen that is harmful to humans and aquaculture in tropical areas. The aim of this study was to understand the role of the two-component signal transduction system KdpDE in regulating the virulence of this species. A ΔkdpE mutant was generated via a markerless knockout. Phenotype analysis showed that the mutant was attenuated in growth, biofilm formation, mobility, ECPase activity, and resistance to H2O2 and antimicrobial peptides under conditions of potassium depletion. A challenge experiment to analyze the virulence of A. dhakensis in zebrafish, via intraperitoneal injection, demonstrated that the clinicopathological signs of infection were dropsy, tail and/or fin bleeding, hepatonecrosis, spleen congestion, and nephrohemia. The LD50 value of the mutant (9.02 × 106 CFU/ml) was 15.6-fold higher than that of the wild-type strain (5.77 × 105 CFU/ml). The survival rate of zebrafish was higher after double immunization (76.7%) than after single immunization with the mutant (36.7%). These data reveal for the first time that KdpDE is associated with the virulence of A. dhakensis. The ΔkdpE mutant is attenuated in virulence and shows high protective efficacy in adult zebrafish after double immunization, and is therefore a promising attenuated vaccine candidate.
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