Comparative assessment of ΔarnA and ΔugdΔarnA mutants of Aeromonas dhakensis as live attenuated vaccine candidates: implications for polymyxin resistance and virulence attenuation.

Abstract

Aeromonas dhakensis is an emerging pathogen responsible for infections in humans, livestock, and aquatic species, posing a threat to public health and aquaculture. This study investigates the roles of two critical genes, arnA and ugd, which are involved in polymyxin resistance, by creating single (ΔarnA) and double (ΔugdΔarnA) deletion mutants in A. dhakensis. The mutants showed impaired motility, increased sensitivity to polymyxin, and altered biofilm formation. Virulence was reduced in zebrafish models, with ΔarnA exhibiting a 2.03-fold increase in median lethal dose (LD), and ΔugdΔarnA showing a 7.13-fold increase. Immunization with these mutants provided significant protection, with survival rates of 65 % and 40 %, respectively, after challenge with the wild-type isolate, compared to the control group. These results underscore the critical roles of arnA and ugd in polymyxin resistance and virulence, highlighting their potential as targets for vaccine development in aquaculture disease control.