Isolation, identification, and pathogenicity analysis of a Vibrio parahaemolyticus strain from Litopenaeus vannamei

A pathogenic bacterium strain 20100612001 was isolated from the hepatopancreas tissue of diseased white shrimp Litopenaeus vannamei. The LD50 challenge assay was performed and the LD50 value was found to be 1.44×106CFU/ml. The cell morphotype was observed to be bacilli,coccoid rod or pear-like and some cells could be observed intensely stained at two poles. The strain was Gram-negative, sporeless and had a single polar flagellum. It formed transparent or translucent round colonies on 2216E solid medium but green or blue-green colonies on TCBS medium. It showed the highest identity to V. parahaemolyticus or Vibrio natriegenis by using fatty acid analysis and Biolog system. Based on 16S rRNA sequencing,the strain is 98.9% identical to several species in Vibrio genus, and the phylogenetic tree revealed that it is most close to Vibrio parahaemolyticus. Taken together, the pathogenic strain 2010060612001 is identified as V. parahaemolyticus.