Identification, characteristics and whole genome analysis of a pathogenic Aeromonas hydrophila ST2616 from diseased Asian swamp eel (Monopterus albus) with hemorrhagic sepsis

This study reports the cause of mass mortality in diseased Asian swamp eel ( Monopterus albus ) with hemorrhagic sepsis in Shanghai. A pathogenic strain of Aeromonas hydrophila MaAh001 was isolated from the blood of diseased eels. Experimental infection confirmed that MaAh001 is the pathogen responsible for mass mortality event. Histopathological examinations revealed this strain caused different tissue damage. The median lethal dose (LD 50 ) of MaAh001 was determined as 3.16 × 10 7 CFU/mL, which is converted to an LD 50 per unit weight of 1.58 × 10 6 CFU/g. Virulence gene test and antibiotic resistance detection indicated that MaAh001 carried 14 virulence factor and four antibiotics resistance genes. Drug sensitivity test showed that MaAh001 was highly sensitive to 16 antibiotics. Whole genome sequencing indicated that the strain has a total length of 4, 893 Mb, the G+C content of 61.2 %, and is registered in the GenBank under the entry number CP141267.1. According to the multilocus sequence typing (MLST) analysis, MaAh001 belonged to A. hydrophila ST2616 (PubMLST database id: 3152). Comparison with the pathogen virulence factor database (VFDB) indicated that this strain carried a variety of virulence genes related to adhesion, invasion and secretion systems. Analysis results of the comprehensive antibiotic resistance database (CARD) showed that MaAh001 carried the most common five β-lactam resistance genes, including cphA2 , OXA-726 , CepS , P26918 and YP_857635 . In conclusion, this study reported a typical case of A. hydrophila MaAh001 strain infection in eels, which laid a theoretical foundation for the prevention and treatment of eel sepsis in aquaculture and the development of subsequent vaccines. • Strain MaAh001 can cause serious pathological damage to Asian swamp eel. • Strain MaAh001 carried 14 virulence factor genes. • Strain MaAh001 carried four drug resistance genes. • Strain MaAh001 is resistant to six antibiotics. • Whole genome analysis revealed the pathogenicity and drug resistance of strain MaAh001.