AUTHOR=Erickson Vera Irene , Khoi Le Minh , Hounmanou Yaovi Mahuton Gildas , Dung Tu Thanh , Phu Tran Minh , Dalsgaard Anders 

TITLE=Comparative genomic analysis of Aeromonas dhakensis and Aeromonas hydrophila from diseased striped catfish fingerlings cultured in Vietnam

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1254781

DOI=10.3389/fmicb.2023.1254781

ISSN=1664-302X

ABSTRACT=<sec><title>Introduction</title><p>Motile <italic>Aeromonas</italic> septicemia (MAS) is a burden for striped catfish (<italic>Pangasius hypophthalmus</italic>) farmers in Vietnam. MAS can be caused by several species of <italic>Aeromonas</italic> but <italic>Aeromonas hydrophila</italic> is seen as the leading cause of MAS in aquaculture, but recent reports suggest that <italic>A. dhakensis</italic> is also causing MAS.</p></sec><sec><title>Methods</title><p>Here we investigated the bacterial etiology of MAS and compared the genomic features of <italic>A. hydrophila</italic> and <italic>A. dhakensis</italic>. We collected 86 isolates from diseased striped catfish fingerlings over 5 years from eight provinces in Vietnam. Species identification was done using PCR, MALDI-TOF and whole genome sequence (WGS). The MICs of commonly used antimicrobials was established. Thirty presumed <italic>A. hydrophila</italic> isolates were sequenced for species confirmation and genomic comparison. A phylogenetic analysis was conducted using publicly available sequences and sequences from this study.</p></sec><sec><title>Results</title><p>A total of 25/30 isolates were <italic>A. dhakensis</italic> sequence type (ST) 656 and 5/30 isolates were <italic>A. hydrophila</italic> ST 251. Our isolates and all publicly available <italic>A. hydrophila</italic> isolates from Vietnam belonged to ST 251 and differed with &lt;200 single nucleotide polymorphisms (SNP). Similarly, all <italic>A. dhakensis</italic> isolates from Vietnam belonged to ST 656 and differed with &lt;100 SNPs. The <italic>tet(A)</italic> gene was found in 1/5 <italic>A. hydrophila</italic> and 19/25 <italic>A. dhakensis</italic>. All <italic>A. hydrophila</italic> had an MIC ≤2 mg/L while 19/25 <italic>A. dhakensis</italic> had MIC ≥8 mg/L for oxytetracycline. The <italic>floR</italic> gene was only found in <italic>A. dhakensis</italic> (14/25) which showed a MIC ≥8 mg/L for florfenicol. Key virulence genes, i.e., <italic>aerA</italic>/<italic>act</italic>, <italic>ahh1</italic> and <italic>hlyA</italic> were present in all genomes, while <italic>ast</italic> was only present in <italic>A. dhakensis</italic>.</p></sec><sec><title>Discussion</title><p>This study confirms previous findings where <italic>A. dhakensis</italic> was the dominating pathogen causing MAS and that the importance of <italic>A. hydrophila</italic> has likely been overestimated. The differences in antimicrobial susceptibility between the two species could indicate a need for targeted antimicrobial treatment plans. The lipopolysaccharide regions and outer membrane proteins did not significantly differ in their immunogenic potentials, but it remains to be determined with <italic>in vivo</italic> experiments whether there is a difference in the efficacy of available vaccines against <italic>A. hydrophila</italic> and <italic>A. dhakensis</italic>.</p></sec>