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 center dot 80% and 4 center dot 90-8 center dot 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 beta-hemolysis were phenotypically observed in 34 (79 center dot 07%), 33 (74 center dot 74%), 30 (69 center dot 77%), 25 (58 center dot 14%), 22 (51 center dot 18%) and 21 (48 center dot 84%) isolates. The virulence genes were detected by polymerase chain reaction (PCR) in following frequencies- aer (86 center dot 05%), hlyA (83 center dot 72%), gcaT (83 center dot 72%), lip (72 center dot 09%), act (67 center dot 44%), fla (65 center dot 12%), ascV (58 center dot 14%), ast (55 center dot 81%), ser (41 center dot 86%), ahyB (39 center dot 53%) and alt (25 center dot 58%). Every isolate was resistant to at least four antibiotics in disk diffusion test. The multiple antibiotic resistance (MAR) index values ranged from 0 center dot 22-0 center dot 50 among the isolates. Our study suggests that zebrafish can be a potential reservoir of virulent and multi-drug resistant Aeromonas spp.