Isolation and Characterization of Bacteriophages from Inland Saline Aquaculture Environments to Control Vibrio parahaemolyticus Contamination in Shrimp

Among the various bacterial pathogens associated with the aquaculture environment, Vibrio parahaemolyticus the important one from shrimp and human health aspects. Though having been around for several decades, phage-based control of bacterial pathogens (phage therapy) has recently re-emerged as an attractive alternative due to the availability of modern phage characterization tools and the global emergence of antibiotic-resistant bacteria. In the present study, a total of 12 V. parahaemolyticus specific phages were isolated from 264 water samples collected from inland saline shrimp culture farms. During the host range analysis against standard/field isolates of V. parahaemolyticus and other bacterial species, lytic activity was observed against 2.3–45.5% of tested V. parahaemolyticus isolates. No lytic activity was observed against other bacterial species. For genomic characterization, high-quality phage nucleic acid with concentrations ranging from 7.66 to 220 ng/µl was isolated from 9 phages. After digestion treatments with DNase, RNase and S1 nuclease, the nature of phage nucleic acid was determined as ssDNA and dsDNA for 7 and 2 phages respectively. During transmission electron microscopy analysis of phage V5, it was found to have a filamentous shape making it a member of the family Inoviridae . During efficacy study of phage against V. parahaemolyticus in shrimp, 78.1% reduction in bacterial counts was observed within 1 h of phage application. These results indicate the potential of phage therapy for the control of V. parahaemoyticus in shrimp.