Isolation and characterization of broad spectrum bacteriophages lytic to Vibrio harveyi from shrimp farms of Kerala, India

Abstract

Of 33 phages isolated from various shrimp farms in Kerala, India, six were segregated to have broad spectrum lytic efficiency towards 87 isolates of Vibrio harveyi with cross-infecting potential to a few other important aquaculture pathogens. They were further tested on beneficial aquaculture micro-organisms such as probiotics and nitrifying bacterial consortia and proved to be noninfective. Morphological characterization by transmission electron microscopy (TEM) and molecular characterization by RAPD and SDS-PAGE proved them distinct and positioned under Caudovirales belonging to Myoviridae and Siphoviridae.

Significance and impact of the study: In sustainable aquaculture, application of antibiotics is prohibited to manage vibriosis, including the one caused by Vibrio harveyi. In lieu of antibiotics, an eco-friendly alternative method, phage therapy, is recommended here. To facilitate the same, a set of six broad spectrum V. harveyi phages, as cocktail, has been constituted and characterized based on morphological traits and by employing molecular tools. These phages were also found to infect other aquaculture pathogens belonging to Vibrio and Aeromonas. Subsequent to in vivo trials, they can find application in shrimp hatcheries as prophylactics and therapeutics.

Keywords: Caudovirales; V. harveyi; V. harveyi phage; broad spectrum phages; lytic phages; phage therapy; soft agar overlay; vibriophage.