Characterization and antimicrobial susceptibility of motile aeromonads isolated from freshwater ornamental fish showing signs of septicaemia

• Published in: Diseases of aquatic organisms 2014-05, Vol.109 (2), p.127-137
• Main Authors: Jagoda, S S S de S, Wijewardana, T G, Arulkanthan, A, Igarashi, Y, Tan, E, Kinoshita, S, Watabe, S, Asakawa, S
• Format: Article
• Language: English
• Subjects: Aeromonas; Aeromonas - classification; Aeromonas - drug effects; Aeromonas veronii; Animals; Anti-Bacterial Agents - pharmacology; DNA Fingerprinting; DNA, Bacterial - genetics; DNA, Ribosomal - genetics; Drug Resistance, Bacterial; Fish Diseases - microbiology; Fishes; Fresh Water; Freshwater; Gram-Negative Bacterial Infections - microbiology; Gram-Negative Bacterial Infections - veterinary; Phylogeny; Phylogeography; Polymerase Chain Reaction; Polymorphism, Restriction Fragment Length; RNA, Ribosomal, 16S - genetics; Sepsis - microbiology; Sepsis - veterinary
• ISSN: 0177-5103; 1616-1580
• DOI: 10.3354/dao02733

A total of 74 phenotypically identified presumptive motile Aeromonas isolates recovered from septicaemic freshwater ornamental fish in Sri Lanka were genetically characterized by sequencing of rpoD and gyrB genes. rpoD/gyrB phylogeny confirmed only 53 isolates as Aeromonas, among which A. veronii was the predominant species (79.2%), followed by A. hydrophila (7.5%), A. caviae (5.7%), A. jandaei (1.9%), A. dhakensis (3.8%) and A. entero pelogenes (1.9%). The aeromonads confirmed by sequencing were further subjected to 16S rDNA PCR-RFLP which substantiated sequencing results for 83% of isolates. Fingerprinting of A. enteropelogenes (n = 42) using ERIC-PCR revealed no dominant clones, and the majority were genetically distinct. All isolates were screened by PCR for 7 virulence determinant genes (aer, act, ast, alt, fla, ser, exu) and 2 integrase encoding genes (intI1, intI2). Each isolate contained ≥3 of the virulence genes tested for, with a heterogeneous distribution. Of the isolates, 77% harboured the intI1 gene, while none had intI2. In vitro antimicrobial susceptibility testing showed highest resistances towards tetracycline (58.5%) and erythromycin (54.7%). Our results indicate the diverse range of aeromonads that could potentially be associated with motile aeromonad septicaemia in ornamental fish. This is the first isolation of A. dhakensis from a septicaemic ornamental fish since its original description from the same host.