Characterization of Vibrio parahaemolyticus isolates from shrimp farms of Southeast coast of India with special reference to Acute Hepatopancreatic Necrosis Disease (AHPND) status

Vibrio parahaemolyticus is an important shrimp & human pathogen and a special strain of it harbouring toxic plasmid can cause Acute Hepatopanreatic Necrosis Disease (AHPND) to shrimp. An attempt was made to isolate and further characterize this bacterium from shrimp farms of south east coast of India. From 381 shrimp farms sampled over a period of four years, 105 isolates were presumptively identified as V. parahaemolyticus. All the 105 isolates were found to be negative for PirA and PirB toxin, characteristic of AHPND V.parahaemolytiucs. The challenge experiments with representative isolates required higher number of bacteria to cause shrimp mortality. The isolates were negative for thermostable direct haemolysin (tdh), tdh related haemolysin (trh) and type III secretion system alpha and beta. The isolates were tested to be sensitive to majority of the antibiotics. This study thus indicates that V. parahaemolyticus isolates recovered from aquaculture ponds of Southeast coast of India are non-shrimp pathogenic and non-human pathogenic. Direct tissue samples (hepatopancreas and stomach) and Tryptic Soy Broth enriched bacteria population from these tissues were also found to be negative for PirA and PirB toxin, characteristic of AHPND. Based on this evidence, AHPND was not detected in any of the samples collected from these shrimp culturing areas.