Phage cocktails: combatting Vibriosis in aquaculture

Aquaculture is one of the fastest growing industries in the world. However, bacterial infections limit the development of production (Oliveira et al., 2012). Vibriosis is responsible for most of the outbreaks, resulting in huge economic costs. The use of antibiotics to combat this has led to resistant strains. Phage therapy can be an eco-friendly alternative to antibiotic treatment in aquaculture systems to prevent and control pathogens. Phage cocktails, containing two or more phages, have the potential to overcome the problem of phage bacterial resistance. The aim of the study by Mateus et al. (2014) was to evaluate the efficiency of cocktails to control Vibrio spp. infections in aquaculture. V. parahaemolyticus was chosen to be used as the bacterial host in this study as it is a human bacterial pathogen which can lead to gastroenteritis contracted from contaminated.

Three phages (VP-1, VP-2 and VP-3) were isolated from the Cortedas Freiras aquaculture system in Portugal. The phages were tested either by themselves, as a combination of two, or all three combined. The occurrence of lysis zones were used to assess bacterial susceptibility to the bacteriophage. Phage survival was determined by calculating the phage titer. The study found that phage therapy using cocktails was significantly more efficient at inactivating V. parahaemolyticus and had higher burst sizes and shorter lytic cycles than single phage treatment. This could be due to the phages exploiting different bacterial receptors to be absorbed by the host. It was also determined that all three phages had a long period of viability in marine water, between five to seven months.

This report is believed to be the first known study on Vibriosis and phage cocktail control. The authors have proved that these cocktails are a viable alternative to antibiotics in aquaculture and the problem of phage resistant bacteria can be circumvented by the use of a combination of phages (Chan et al., 2013). All phage cocktails were found to be more efficient at controlling bacteria growth than single phages. Phage cocktails have an increased efficiency with a higher and faster rate of inactivation and a delay in the development of bacterial resistance. This could lead to a more effective and environmentally friendly method of controlling pathogens in aquaculture systems. However, they did not prevent bacterial regrowth and would likely have to be reintroduced into the systems periodically. There is a high potential for expansion of the use of phage cocktails in aquaculture which will require further research and the identification of crucial pathogens.

In conclusion, the important findings of this paper show that phage cocktails with two or three phages increase the efficiency of phage therapy against Vibrio, delay the development of resistance by the bacterial host and high burst sizes and short latent periods increase the efficiency of bacterial inactivation. Also, phages have a long period of survival in the environment are more efficient. The identification of these characteristics will help recognise the most effective phages in the future. This knowledge is greatly beneficial to the continual development of the aquaculture industry.

Reviewed paper:

Mateus, L., Costa, L., Silva, Y., Pereira, C., Cunha, A., & Almeida, A. (2014). Efficiency of phage cocktails in the inactivation of Vibrio in aquaculture. Aquaculture, 424-425, 167-173. http://dx.doi.org/10.1016/j.aquaculture.2014.01.001

Other mentioned papers:

Chan, B.K., Abedon, S.T., Loc-Carrillo, C., 2013. Phage cocktails and the future of phage therapy. Future Microbiol 8, 769–783.

Oliveira, J., Castilho, F., Cunha, A., Pereira, M., 2012. Bacteriophage therapy as a bacterial control strategy in aquaculture. Aquac. Int. 20, 879–910.