Isolation and characterization of Vibrio cholerae O139 associated with mass mortality in Penaeus monodon and experimental challenge in postlarvae of three species of shrimp

• Mass mortality from cultured postlarvae of P. monodon from a farm in Ernakulam District, Kerala, India is reported.
• The causative agent was confirmed as belonging to V. cholerae O139 serogroup, the causative agent of cholerae to human.
• LD50 value of V. cholerae O139 isolate in postlarvae ranged from 4.6x104 for L. vannamei to 7.1x106 for P. monodon.
• This is the first report of V. cholera O139 strain causing high mortalities in shrimp.

Mass mortality in cultured postlarvae of Penaeus monodon from a farm in Ernakulam District, Kerala, India was reported. Yellow colonies from TCBS plates were randomly picked and were confirmed as Vibrio cholerae by conventional biochemical tests and 16S rRNA sequencing. The isolates were confirmed as belonging to the V. cholerae O139 serogroup, generally considered as the causative agent of cholera to humans, using an O139 serogroup-specific antiserum and by a PCR based assay targeting the rfb-O139 gene. The isolates were found to be carrying the cholera toxin producing gene, ctx, and genes coding for virulence determinants, zot and tcpA, as revealed by PCR. Shrimp larvae experimentally exposed to V. cholerae exhibited significant mortalities that increased with increasing doses of bacteria. The LD50 value of one of the isolates was determined in postlarvae of P. monodon, Fenneropenaeus indicus and Litopenaeus vannamei and ranged from 4.6 × 104 for L. vannamei to 7.1 × 106 for P. monodon. V. cholerae was re-isolated from the larvae of experimentally infected moribund shrimps. Histopathological examination revealed rupture of the basal laminae of the hepatopancreatic tubules and severe necrosis. To our knowledge, this is the first report of the V. cholerae O139 strain causing high mortalities in shrimp.