Influence of some environmental variables and addition of r-lysozyme on efficacy of Vibrio harveyi phage for therapy

ABSTRACT

Bacteriophage therapy is a viable proposition for controlling luminous vibriosis caused by Vibrio harveyi in shrimpaquaculture. However, environmental factors influence the growth and activity of phage and affect its efficiency incontrolling bacterial diseases. An essential problem in the use of vibrio phage as a therapeutic agent was the development ofresistance to phage attachment, rendering them resistant to the lytic action of phage. This problem could be overcome byapplying a cocktail of phages. This study aimed to evaluate the effect of salinity and pH on the phage activity and also tostudy the role of recombinant shrimp lysozyme on the performance of the V. harveyi phage. Out of three different levels ofsalinity (20, 25 and 30 ppt) and pH (6, 7 and 8) tested, optimum phage activity was observed at a salinity of 25 ppt and atneutral pH. Application of recombinant shrimp lysozyme in combination with V. harveyi phage significantly improved theactivity of phage in in vitro assay as well as in microcosm study using seawater. The application of phage along withlysozyme can be a useful approach to overcome the inability of phage to enter the bacteria and thus eliminate or reduce fish/shrimp pathogenic bacteria in aquaculture.