Isolation and characterization of vibrio bacteria from acute hepatopancreatic necrosis diseased whiteleg shrimp (Litopenaeus vannamei) cultured in the Mekong Delta

Abstract

Acute hepatopancreatic necrosis disease (AHPND), a farmed penaeid shrimp bacterial disease originally known as early mortality syndrome (EMS). In 2013, the causative agent was discovered to be the only isolates of Vibrio parahaemolyticus containing the 69 kbp plasmid. This study was conducted to isolate and identify Vibrio bacteria from Litopenaeus vannamei infected with AHPND. Field sampling was conducted in Ben Tre, Tra Vinh,Soc Trang, Bac Lieu and Ca Mau provinces. Disease signs at pond level included pale hepatopancreas (HP), significant atrophy of the HP, guts with discontinuous contents or no content and mortality starting as early as 10 days post stocking.The isolated bacteria were Gram-negative, short rod-shaped, motile, and positive with oxidase and catalase, with green colonies on TCBS and bluish green colonies on hicrome agar plates. The bacteria were identified as Vibrio parahaemolyticus (99.9% ID) by using API 20E kit (BioMerieux) and confirmed by positive result with PCR analysis using primer pair to detect the specific gene of V. parahemolyticus. Result in analysis tissue structure on hepatopancreas recorded is structurally changed, degeneration and necrotic sloughing of the HP tubule epithelial cells, accompanied by a decrease of R, B and F-cells, karyomegaly, formation of melanized granulomas.