Bacteriophages: an alternative to antibiotics for fish farms?

30-Jan-2017 - Last updated on 30-Jan-2017 at 11:26 GMT

An EU-funded project led by the Spanish marine environment and food technology center AZTI is close to determining whether bacteriophages could be a viable alternative to antibiotics for destroying pathogens in aquaculture.

The €800,000 Enviphage project, co-funded by the European LIFE program, is in the final stages of evaluating the environmental impact of bacteriophages by establishing the effect of the technology on marine micro-organisms and fish.

Bacteriophages - viruses that infect and destroy bacteria - are produced by fermentation via a technology that is similar to bacterial starter production. Up until now, scientists have obtained promising results in laboratories that suggest they could be used as an alternative to prophylactic antibiotics in feed for preventing diseases in fish farms. However, the use of bacteriophages on an industrial scale requires knowledge of their environmental impact.

“We know that antibiotics modify the environmental bacteria populations, and before using bacteriophages, we have to be sure about the effect of phages on the natural bacteria population,” Igor Hernandez, researcher at AZTI and Enviphage project coordinator, told FeedNavigator.

The problem with antibiotics…

When antibiotics are provided as part of fish food, unconsumed food and fish faeces containing antibiotics settle at the bottom of raising pens and/or are transported by the water and discharged into the environment, where antibiotics can be ingested by wild fish or settle in sediments. Once in the environment, antibiotics alter the composition of the microbiota, with antibiotic resistant bacteria taking over from non-resistant bacteria. This has potentially serious environmental and human health consequences.

Much effort has been made to find environmentally friendly alternatives to antibiotics as prophylaxis agents in aquaculture. However, alternative prophylaxis is not possible in very small fish, among which the losses are greatest, so larvae and young fry are still dependent on antibiotic treatments. Also, vaccines are useless for treatment of shellfish.

An environmentally-friendly alternative?

Bacteriophages present one promising alternative, and because they are highly specific, scientists believe they have limited effects on environmental bacterial ecology.

“In theory, bacteriophages are so specific that they should not introduce any modification in the population structure, but nobody has demonstrated this point up until now,” said Hernandez.

Bacteriophages offer other advantages over antibiotics too, according to Hernandez.

“Preliminary results indicate that the cost of phage production would be much lower than antibiotic production. Bacteriophages would also offer other advantages compared with antibiotics, such as the absence of residues, the fact that no security period is necessary before marketing them and the ability to add them to water for fry and egg treatments,” he said.

Impregnated fish feed is one delivery route for bacteriophage therapy.

Genetic technologies

This final stage of the four-year Enviphage project is studying the effect of bacteriophages on the bacterial population via NGS (next generation sequencing) technology, which Hernandez describes as “the most accurate method for population description available at this moment."

During 2014 and 2015, the project focused on selecting the most suitable bacteriophages for evaluation, namely those that are most active against pathogenic micro-organisms in fish. During 2016, significant quantities of these phages have been produced for treating fish at an aquaculture facility at Ria de Aveiro in Portugal. Environmental and fish samples were taken to determine the effect of this technology on marine micro-organisms, on the micro-organisms present in the fish and on the animals themselves.

The results are expected this year, following analysis of the metagenomic data characterizing the bacteria present. But even if - as the researchers expect - the findings are positive, there will still be other obstacles to overcome before bacteriophages are accepted as a commercial alternative to antibiotics, according to Hernandez:

“There are several obstacles. First is the absence of clear legislation governing the use of these antibacterials. Second is the absence of commercial phages available for this treatment in aquaculture. But probably the biggest obstacle is that bacteriophages are little known among fish farmers.”