Characterisation of bacteriophage and bacteriophage cocktails from agricultural sources as potentially novel antimicrobial agents

The threat of antimicrobial resistant (AMR) pathogens to ONE Health is ever looming due to the mistreatment and liberal use of antibiotic treatment. It is becoming difficult to treat infections when the bacteria causing them are becoming resistant to currently available antibiotics. To this end, Lord Jim O’Neill has recommended researching alternative treatments to support the fight against AMR. Bacteriophages (phages) are viruses abundant in nature that attach to and lyse bacteria in order to increase their population, are one such alternative. Studies regarding phages date back as early as 1915, where English microbiologist Frederick Twort first discovered them. However, it would be French – Canadian microbiologist Felix d’Hérelle who would first publish his findings about phages ‘antagonising’ bacteria.

This project isolated phages from agricultural sources such as soil, liquid runoff, pig, and cow faeces by screening them against ten randomly selected strains of Escherichia coli in addition to bacteria present within the soil pellet. Plaque assays were conducted to investigate the presence of phages within collected samples. Host range was determined by conducting promiscuity tests against twenty-four randomly selected bacteria, using phenol red broth as an indicator for bacterial growth. The bacteria were: Escherichia coli, Klebsiella sp., Proteus vulgaris, Proteus mirabilis, and Streptococci. Serial dilutions were performed to assess the killing titre of isolated phages, which proved useful for the phage cocktail experiments. Ten phages were cocktailed and tested against a mixture of compatible bacteria to assess killing efficacy over time via spectrophotometry. A complementary study was performed to investigate how pairing phages of varying killing titres would affect the overall killing efficacy of a cocktail.

This study found that the agricultural phages isolated had low host range and low killing titres. Additionally, the study found that low killer phage cocktails performed well at high concentrations, but saw reduced efficacy at low concentrations, with high killers showing promise at a range of concentrations. With this potential in mind, further research and testing of current methods of standardised phage isolation, purification and concentration is recommended to ensure killing capabilities equivalent to high titre phages.