Aeromonas dhakensis is a formidable pathogen and has emerged as a significant threat due to its ability to inflict severe infections in aquatic organisms and humans worldwide. The pathogenicity of A. dhakensis is multifactorial, involving a large number of virulence factors such as hemolysins, aerolysin, proteases, cytotoxins, and secretion systems (mainly Type II and Type III) which help the bacteria invade the tissue and evade the immune system. In this research, we report the first-time isolation of A. dhakensis from diseased mangrove red snapper reared in cage systems of Kerala, India.
In the present study, we also report the first whole-genome sequencing and analysis of A. dhakensis KS130825 strain, thus 35 million reads (Q30 > 94%) were generated and the genome was assembled into 27 contigs (total length = 4,725,118 bp; N50 = 614,135 bp; GC = 61.75%). Genome annotation revealed 4,380 coding sequences and Resistome analysis revealed a multitude of resistance determinants, such as β-lactamases, the quinolone resistance protein QnrB, and genes for a multidrug efflux pump (macA, macB, tolC). Besides this, resistance-conferring genes via target modification (gyrA, gyrB, rpoB) and regulatory proteins (OxyR, H-NS) were also detected. The virulome contained 136 genes (VFDB) associated with hemolysins, secretion systems (Types II/III), biofilm formation, and adhesion. Subsystem analysis showed the main functions to be stress response, metabolism of aromatic compounds, and metal ion transport. Phylogenetic analysis (RAxML) aligned the isolate with clinical A. dhakensis strains, thereby suggesting zoonotic potential. Parallelly, antibiogram profile has been completed and found the isolate was phenotypically susceptible to the antibiotics tested. The presence of such latent genetic determinants represents a potential risk for the rapid emergence of resistance when selective antibiotic pressure exists in the environment. Interestingly, WGS also has uncovered the convergence of virulence, environmental persistence, and genomic plasticity in addition to the presence of unexpressed but yet potentially activatable resistome. This discovery underscores the limitations of conventional susceptibility testing and highlights that genomic surveillance is crucial to locating the cryptic antimicrobial resistance determinants.