Genetic relationship of pathogenic Vibrio parahaemolyticus isolated from aquaculture farms and hatcheries

Abstract

Despite stringent preventive actions being taken by the industrialists Vibrio sp. remains to be a major concern during the export of shrimp as evidenced by the data given in RASFF portal of the EU, which notifies the border rejection of two consignments and notification issued for four others in last one year from August 2016 to August 2017. Among the six consignments that were positive for Vibrio parahaemolyticus, three were from India. The presence of V. parahaemolyticus in the consignments can be attributed to its innate prevalence in saline environments of tropical areas. A study was conducted on the prevalence of V. parahaemolyticus in samples collected from aquaculture farms and hatcheries of Kerala during the period from 2014 to 2016. 42 samples including water, mud and shrimp were collected from 12 farms and 3 hatcheries of which 93 per cent were positive for V. parahaemolyticus. 33 pathogenic isolates of V. parahaemolyticus, determined by the presence of either thermostable direct haemolysin (tdh) gene, tdh related haemolysin (trh) gene or Kanagawa phenomenon was isolated from as many as 7 samples. The pathogenic isolates were further subjected to ERIC PCR to understand the genetic relatedness among the isolates. The analysis of ERIC PCR fingerprints revealed extensive diversity among the isolates. At 40 per cent similarity, six major clusters were identified in the dendrogram. The clustering of isolates from different farms located in the same geographical location with high similarity represented the regional spread of these isolates. The isolates that were clustered together with the reference clinical isolate were positive for tdh geneindicating genetic relatedness between these isolates. The study can be further extended to determine the genetic relationship of V. parahaemolyticus from frozen and processed samples which will help in elucidating the possible source of contamination.