Phage therapy means using bacteriophage/phages capable of killing the bacterial pathogens, for treating the disease caused by that bacterial pathogen. Using this method of disease treatment has a number of benefits such as particular phage specifically target bacterial pathogen and other bacteria (including beneficial associated microbes) remain unaffected, as density of bacterial pathogen decreases, consequently phage concentration also declines. The same authors have previously reported isolation and characterisation of lytic phages for two bacterial pathogens of corals. This study particularly looked at treatment of white plague-like (WPL) disease in a coral species Favia favus, caused by a bacterium Thalassomonas loyana.
Field experiments were conducted in the Red sea of Eilat, Israel. The study was conducted by injecting phage BA3 (capable of infecting specifically T. loyana) to the treatment which was compared to controls which were without the dose of phage. The experiments were conducted for two times, firstly in 2009 and then in 2011. Corals from these treatments were transferred in aquaria and divided as per their healthy/diseases status. Phage concentration in these aquaria waters was measured by soft agar overlay technique. Coral samples were prepared and used for identification of T. loyana by 16S rRNA gene sequencing.
The authors noted little reduction in the living tissue in the phage treated corals whereas in the non-treated controls, living tissue was significantly reduced along with the mortality of few diseased corals. They also noted that phage treatment also significantly reduced transmission of WPL disease.
If phage therapy is to be operated on a large scale for treating coral diseases, developing a technique for delivering phages to infected corals over a large area, production of sufficient phages for treating large area of a reef and convincing local authorities for safety of this therapy by providing necessary evidence, would be required. Regarding concentration of phages required for treating the disease, authors showed that 103 phage per ml (which is a thousand times higher than their natural abundance in Eilat seawater) is enough to prevent the spread of WPL. Extrapolating these figures, the authors suggested that production of sufficient phages to treat a large area of a reef is possible. Nevertheless, authors did not address issues such as feasibility of phage therapy on reefs, in terms of its costs and effectiveness. Similarly, they did not address any limitations of it. A limitation which I can think of is its applicability to only few bacterial diseases which are caused by a single bacterial pathogen, but what about diseases like black band disease which is caused by a consortium of pathogens?
This study proves that phage BA3 can be effective against progression and transmission of WPL disease. Interestingly, as BA3 phage can only infect T. loyana; this study also confirms that T. loyana is the causative agent of WPL disease. This discovery led authors to suggest that in nature, phages may be playing a role in making few of the corals naturally resistant to certain bacterial diseases, which I found thought provoking. As authors suggested, perhaps, this is why many times healthy corals are surrounded by diseased corals. Could the phages of Vibrio shiloi have played any role in making the coral Oculina patagonica resistant against V. shiloi? The authors could have discussed this idea of “can phages confer resistance against bacterial pathogens?” in the context of coral probiotic hypothesis and hologenome theory of evolution. The discussion of this paper is very short and I think it is incomplete. I think this is a revolutionary idea that phages could play a role in providing natural resistance to organisms against bacterial diseases. How widely applicable this idea would be? Could we link it to natural resistance of few individuals to a bacterial disease epidemic of humans and other animals?
Atad, I., Zvuloni, A., Loya, Y., & Rosenberg, E. (2012). Phage therapy of the white plague-like disease of Favia favus in the Red Sea. Coral reefs, 31(3), 665-670.