BACTERIOPHAGES – A NATURAL ALTERNATIVE TO ANTIBIOTICS FOR THE CONTROL OF BACTERIAL INFECTIONS IN AQUACULTURE

Vibriosis is one of the major bacterial diseases of shrimp larvae in hatcheries and juveniles in farms causing huge economic loss of up to 30 % decrease in gross production leading to losses.

The misuse of antibiotics to control infections in aquaculture has resulted in the development of resistant strains, which have rendered antibiotic treatments ineffective. Moreover, the horizontal transfer of resistance determinants to human pathogens and the presence of antibiotic residues in aquaculture products for human consumption constitute important threats to public health.

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;
•  Self-replicating therapeutic
• Self-limiting -Phages thrive in the presence of bacteria, and die out in their absence.
• One phage/bacterium is sufficient
• “Green Natural Alternative” to antibiotics
• No damage to normal (beneficial) flora
• Removal of the biofilms formed by the bacteria.
• Enhances the probiotic performance.

The use of phages for the biological control of pathogens of cultured fish and shrimp has developed interest in recent years since no drugs residues, drug toxicity is associated with this type of therapy

Bacteriophage therapy will be a major breakthrough in the treatment of vibriosis

The advantage of phage therapy in vibriosis are

• Increase in shrimp production by avoiding loss due to vibriosis.
• Increase in acceptance of the shrimp in global market due to the decrease in use of antibiotics.
• A major social advantage is prevention of spread of antibiotic resistant bacteria and residual antibiotics in the meat consumed by human.

 In our facility several phages have been isolated, characterized and formulations have been made and has been widely used in the Indian market.

CHALLENGE STUDIES

 100 Post larvae were challenged with the bacteria and the respective phages.  All the tanks with phages shows marked survivability when compared to control tank which contained only bacteria.  A cocktail of phage 1a, VH20, VH3 and phage 1a, VH19 and VH3 were also used in the above study and 3 trials of challenge studies were conducted at Aristogene and 2 at NCAAH, Cochin.   All these studies prove that protection by phages was as good as antibiotics.

Field Trials:

• Several trials showed that the larval survivability increased markedly with the bacteriophage therapy.
• Commercial hatchery results:  Bacteriophage cocktail has been used for over one year in Andhra Pradesh, India and the survival results are reportedly 10-15 % higher than the best probiotics available.
• 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, increase in survival and increase in Average daily weight gain.
• Field trials in nursery in Costa Rica has shown that phages were able to control EMS (early mortality syndrome)

Results:

• Drastic reduction of total vibrio counts
• Reduction of Running mortality syndrome
• Control of White faecal disease
• Protection against EMS
•  Bacteriophage therapy can be stand alone therapy or can be used in adjunct with probiotics.
• There has been increase in survival, better FCR and protection from vibriosis.

 The results of treatment trial in a farm affected with running mortality syndrome