Characterization of virulence properties and multi-drug resistance profiles in motile Aeromonas spp. isolated from zebrafish (Danio rerio).

Aeromonas spp. are opportunistic pathogenic bacteria associated with a multitude of diseases in ornamental fish. In this study, virulence properties and antibiotic resistance patterns of 43 Aeromonas strains isolated from 46 zebrafish were investigated. The isolates were identified as Aeromonas veronii biovar veronii (n = 26), A. veronii biovar sobria (n = 3), Aeromonas hydrophila (n = 8), A. caviae (n = 3), Aeromonas enteropelogenes (n = 2) and Aeromonas dhakensis (n = 1) by gyrB gene sequencing. The sequence divergence within and between the species ranged from 0-5·80% and 4·90-8·00%. Each species formed a distinct group in a neighbour-joining phylogenetic tree. The lipase production, biofilm formation, DNase activity, gelatinase production, caseinase production and β-hemolysis were phenotypically observed in 34 (79·07%), 33 (74·74%), 30 (69·77%), 25 (58·14%), 22 (51·18%) and 21 (48·84%) isolates. The virulence genes were detected by polymerase chain reaction (PCR) in following frequencies- aer (86·05%), hlyA (83·72%), gcaT (83·72%), lip (72·09%), act (67·44%), fla (65·12%), ascV (58·14%), ast (55·81%), ser (41·86%), ahyB (39·53%) and alt (25·58%). Every isolate was resistant to at least four antibiotics in disk diffusion test. The multiple antibiotic resistance (MAR) index values ranged from 0·22-0·50 among the isolates. Our study suggests that zebrafish can be a potential reservoir of virulent and multi-drug resistant Aeromonas spp. SIGNIFICANCE AND IMPACT OF THE STUDY: Aeromonas spp. are Gram-negative and facultative anaerobic bacteria which are ubiquitous in aquatic environments. Virulence properties and antibiotic resistance of ornamental fish-borne Aeromonas spp. are poorly understood. The virulence factors as well as multiple antibiotic resistance profiles of zebrafish-borne Aeromonas spp. were characterized for the first time in Korea. Most of the isolates were positive for phenotypic virulence traits and harboured several virulence genes revealing the virulence potential of zebrafish-borne Aeromonas spp. Additionally, the high multiple antibiotic resistance (MAR) index values displayed by the isolates highlight the necessity of responsible use of antibiotics in the ornamental fish industry.