Aeromonas is one of the most virulent fish pathogens known. Aeromonas hydrophila causes a fish disease known as "Aeromonas or Hemorrhagic Septicemia or Motile Aeromonas Septicemia or Ulcer Disease or Red-Sore Disease". Management involves both prophylactic and therapeutic use of antibiotics. Unfortunately, the indiscriminate use of antimicrobial agents has led to the development of resistant strains of bacteria. The need for alternative strategies other than antibiotics has stimulated research into lytic bacteriophages because of the lower chance of bacteria developing resistance. This study assessed the effect of using bacteriophages on Aeromonas hydrophila in the treatment of tilapia fish Aeromonasis.
The host was resuscitated and reconfirmed using biochemical tests and genetic profiling. The profiled bacteriophage was bulked up and enumerated using the overlay agar method. Bacteriophage stability in tank water for Ph and temperature levels was established. Fish fingerlings of an average weight of 5 gms were acclimatized, put in aquarium glass water tanks and separated into test and control subjects. Test subjects were divided into two groups, one inoculated with bacteria, stressed through delayed feeding and bacteriophages added to the tanks. while the second test group had bacteriophage added without stress. The control groups were not inoculated with either bacteria or phages.
Bacteriophages exhibited stability at both pH 6-9 in tank water. The bathing method was found to be effective for fish challenge and phage application. Stress influenced fish disease in the tanks. A multiplicity of infection of 0.01, 0.1, and 1 showed efficacy on clearing with no differences, while 10 and 100 had outstanding results. Bacteriophage dissociation took around 14 days from the treatment day.
The survival curves plotted using GraphPad Prism version 5 using the Log-rank (Mantel-Cox) test revealed a significant difference in the survival of fish (Chi square = 20.92, df =2 and P value <0.0001 in both test and control groups. The non-parametric test for differences in the survival curves, using the Gehan-Breslow-Wilcoxon test, revealed a significant difference between the curves (χ² = 19.67, df = 2, P < 0.0001).
Use of a single phage isolate showed control of Aeromonas hydrophila infection in water tanks. Direct administration of phages to tank water is an effective route for both phage application and bacterial challenge. Future studies were recommended to establish phage stability in pond water and the need to test the survival of fish in pond water infested with Aeromonas hydrophila using cocktail phage prepared from the three profiled isolates.