Acanthamoeba-Bacteria-Bacteriophages Interactions

In nature, bacteria are frequently exposed to predation by bacteriophages and protozoa. These two microbial groups were described as the main causes of bacterial mortality. Yet, bacteria were found to co-exist and thrive in the presence of both predators.

This study was established to investigate whether the presence of Acanthamoeba can protect bacteria from killing by bacteriophages. Gentamicin protection assay was used to determine the ability of P. aeruginosa WB1 and E. coli 4s to intracellularly survive within Acanthamoeba castellanii cells. Later, bacteria retrieved form gentamicin protection assay were subjected to phage infection. Phages were applied in a form of single and combination treatments. Results have indicated that P. aeruginosa WB1 and E. coli 4s were not able to intracellularly survive within the amoebal cells and were digested by 99%. And, single-phages were effective in a single-enemy system (phage-bacteria system) but were not effective in multiple-enemies system (in Acanthamoeba presence), while, phage combinations showed higher efficiency in eradicating bacterial numbers in both systems.

In addition, this study has investigated the ability of phages to internalise and survive within Acanthamoeba cells. Two experiments were performed, first, the ability of phages to survive inside Acanthamoeba cysts was assessed. Non-nutrient agars were seeded with bacteria infected with phages, then, Acanthamoeba trophozoites were introduced and incubated at room temperature for two weeks to induce encystation. Later, cysts were exposed to acid (2% (v/v) HCL) treatment, UV radiation and extreme heat to assess Acanthamoeba ability to protect phages from hostile conditions. Second, phages (without bacterial hosts) were co-cultured with trophozoites and exposed to UV radiation and extreme heat. Results have indicated that phages were able to intracellularly survive within Acanthamoeba cells. Phages were found more resistant to adverse conditions once trapped within Acanthamoeba cysts, as well as, in the presences of amoebal trophozoites.