Bacteriophages of Vibrio harveyi and their potential to control V. harveyi infection in aquaculture

Wasantha Gunawardhana

Research output: ThesisDoctoral Thesis

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[Truncated abstract] Vibrio harveyi is a devastating pathogen in prawn aquaculture and multiple antibiotic resistant strains are being reported in prawn hatcheries. This suggests the use of antibiotics in aquaculture to control or prevent V. harveyi infection will become progressively less effective. The use of bacteriophages as biological control agents in aquaculture provides an alternative strategy, and was investigated in this study. Twenty V. harveyi phages were isolated from surface seawater (Fremantle, WA, Australia) and characterised using host range, restriction enzyme analysis, pulsed field gel electrophoresis (PFGE), transmission electron microscopy and the presence of DNA sequences associated with virulence genes. All phages had double stranded DNA and genome sizes (based on PFGE) of 57.5–143.5 kb. The phages had morphologies consistent with the families Siphoviridae (17) and Myoviridae (3). They had moderate host ranges compared with previously studied V. harveyi phages; 38% were able to lyse 49–58% of the 43 V. harveyi isolates tested but no phage was able to lyse more than 58% of the isolates. Based on the studied properties these represent a collection of diverse V. harveyi phages. The V. harveyi isolates (46) used in this study varied in pathogenicity to freshly hatched Artemia nauplii. Two V. harveyi isolates (Vh1 and CO71) were highly pathogenic to Artemia, causing 80–100% mortality after 72 h. All tested V. harveyi isolates showed lipase activity, 31 (77.5%) showed protease (caseinase) activity and 32 (80%) showed haemolytic activity (on 5% sheep blood). There was no correlation between the lipase, or haemolytic activities of V. harveyi in this study and mortality to Artemia, but a moderate negative correlation (p <0.05) between protease production and Artemia survival was observed, consistent with previous reports on protease as a virulence factor in V. harveyi. A laboratory biocontrol model was developed using Artemia as the test
Original languageEnglish
QualificationDoctor of Philosophy
Publication statusUnpublished - 2009


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