BACTERIOPHAGE BASED CONTROL OF VIBRIOSIS IN AQUACULTURE

The shrimp industry ranks as the highest foreign exchange earner among our marine product exports. Asian countries like Indonesia, Thailand and India have emerged as global leaders in shrimp production. Aquaculture is the most rapidly expanding sector in food production, yet the most vulnerable to losses caused by disease.   Among the groups of pathogenic microorganisms, vibriosis is the well-known cause of severe economic losses and responsible for massive mortality of cultured shrimp, fish and shellfish. An intensive mode of culture with high stocking density has resulted in increase in the incidence of diseases.  To maintain productivity of such intensive aquaculture massive use of antibiotics has been employed. The spread of antibiotic resistance from aquaculture settings to the natural environment is increasing.  About 70% of the Vibrio isolated from aquaculture settings is multi-drug resistant. 

Another concern associated with the use of antibiotics is the problem of residues, which has resulted in rejection by seafood importing countries of shrimp containing traces of antibiotics. Alternative strategies must be developed to control diseases in aquaculture. These strategies should reduce the risk of developing and spreading microbial resistance and more environment friendly.

Today, unless concerted action is taken to curb antibiotic overuse and misuse, in humans and animals, the world may be heading for a post-antibiotic age.

Bacteriophage Therapy

Bacteriophage therapy is currently considered as a viable alternative to antibiotics for the treatment of bacterial infections in aquaculture systems. The use of bacteriophages to control bacterial infections in aquatic food production system has the promising potential to address the twin problem of controlling bacterial infections and at the same time avoiding residue contamination.

The application of phages in aquaculture has good advantages over the use of antibiotics.

• This includes the targeted attack of vibrios by phages, phages are abundant in nature, no serious side effect; On the contrary, antibiotics target both pathogen and normal micro-flora, which have multiple side effects;
• Self-replicating therapeutic
• Self-limiting -Phages thrive in the presence of bacteria and die out in their absence.
• “Green Natural Alternative” to antibiotics
• No damage to normal (beneficial) flora

The present study is aimed at assessing the potential advantages of using bacteriophages against vibrios in shrimp culture. 

Field Trials:

• Several Field trials showed that the larval survivability in the hatcheries increased markedly with the bacteriophage therapy.
• Use of phage therapy in grow-out culture:  Phage cocktail against vibriosis was also mixed with feed and fed to animals which showed that there is a decrease in the vibrio counts in the gut of animals, decrease in running mortality, White faecal disease, increase in survival and increase in Average daily weight gain.
• Bacteriophage-based formulation against vibrios resulted in better growth, survival, FCR and quality of marine shrimp Penaeus Vannamei.
• The trials have demonstrated the potential of vibrio-specific phages to significantly reduce the impacts of vibrios, with a resulting positive effect on shrimp survival.  Therefore, phage therapy may be a realistic alternative approach for controlling pathogenic bacteria in aquaculture owing to its several advantages over the conventional antibiotics and other methods against pathogenic multiple drug resistant (MDR) bacteria.