BACTERIOPHAGE THERAPY TO REDUCE PATHOGENIC VIBRIOS IN MOLLUSCAN SHELLFISH AQUACULTURE

Minimizing the effects of vibrios in molluscan shellfish is a formidable task. From larval  mortalities caused by  pathogens like  Vibrio coralliilyticus (Vc )  and  Vibrio tubiashii  (Vt)  to human  pathogenic vibrios , like Vibrio parahaemolyticus (Vp )  and Vibrio vulnificus (Vv )  in market shellfish, new innovative approaches are needed to alleviate outbreaks. L arval oyster  mortalities in the US have reached  unprecedented levels with the largest East Coast hatchery experiencing major losses  in 2019  due to unexplained mortality events. West Coast hatcheries continue to experience sporadic mortality events that have limited the availability of seed oysters needed for commercial aquaculture operations.  Many outbreaks have been associated with Vc , which is more pathogenic to shellfish at elevated seawater temperatures.  Interventions to reduce vibrios in shellfish have become more urgent as vibrio pathogenicity in the environment appears to be increasing. Technological advancements, like the development of bacteriophage-based methods to reduce Vc and V t in hatcheries, are showing  great promise , while the application of bacteriophage (phage)  therapy  against vibrios is expected to reduce pathogenic vibrios in market shellfish.

We isolated  and characterized  from Hawaiian seawater  phages that have broad specificity toward eight strains of Vc.  A  three-phage  cocktail reduced  larval oyster  mortalities by over 80% in hatchery trials. The cocktail had no negative effects on larval development or motility.  Commercialization of this cocktail is being sought.

During a  survey  of  Delaware Bay oysters, we frequently isolated phages against potentially dangerous,  pandemic strains of Vp from three harvesting sites. Characterization of phage isolates revealed tailed and non-tailed phages. T hese phages  are earmarked for short-term treatments in  phage therapy  trials of market-sized oysters in a depuration-like system . Phage-based technologies  are offering new avenues to  enhance  shellfish hatchery and commercial oyster operations.