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Farida Mazumder*, James Munro, Mary Barton, and Stephen Pyecroft
School of Animal and Veterinary Sciences
University of Adelaide
Adelaide, SA 5371

Antibiotic resistance is becoming a global problem resulting in the inefficiency of antimicrobial drugs. The problem caused by multidrug resistant bacteria and the limited number of control strategies, highlights the need for alternative control approaches in aquaculture sector. Bacteriophage therapy demonstrates excellent and promising results at both national and international research. This project will support the use of bacteriophage therapy within aquaculture from a research setting into the commercially viable products as a therapeutic option for veterinarian use within the industry.

The present study will be dealing with the bacteriophages active against Aeromonas hydrophila bacteria which is a facultative fish pathogen. Silver perch fish will be used as a model to design the bacteriophage therapeutic tool after successful isolation and characterisation of Aeromonas phages.

With a view to isolating Aeromonas phages, Water samples from different waste water treatment plants (three samples from Bolivar waste water treatment plant and one sample from Glenelg waste water treatment plant) and sewage plant (one sample from Roseworthy sewage plant) were collected and bacteriophages were isolated from those samples through enrichment technique. Ten different strains of Aeromonas hydrophila were used for isolation of Aeromonas phage from five water samples. Isolated bacteriophages were purified by serial dilution of a single plaque on tryptic soy agar plate. Final stocks of purified phages were preserved at 4 °C in SM buffer. Bacteriophage identification was carried out by phage nucleic acid digestion and by observing their morphology using Transmission Electron Microscope (TEM). Phage nucleic acid digestions were carried out using RNase A, S1 Nuclease, BamH1, EcoRI, and PstI.

Out of ten strains of Aeromonas hydrophila, four were positive for plaque formation on tryptic soy agar plate. A total of thirteen bacteriophages were isolated from five different samples applied on ten Aeromonas lawns. The final phage stock titres were 108 pfu/ml. Nucleic acid digestions revealed that all isolated phages were dsDNA viruses. TEM images (FIGURE 1) of the isolated phage samples showed that they have polyhedral head (>60nm diameter) with a long non-contractile tail (230 - 280 nm long). These features confirmed that the isolated Aeromonas phages belong to the Siphoviridae family. The isolated phages will be further applied on Aeromonas infected Silver Perch fish models to study therapeutic effectiveness as well as fish immune response to the bacteriophages.    

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