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

Abstract

Mass mortality in cultured postlarvae of Penaeus monodon from a farm in Ernakulam District, Kerala, India was reported. Yellowcolonies fromTCBS plateswere randomly picked andwere confirmed as Vibrio cholerae by conventional biochemical tests and 16S rRNAsequencing. The isolateswere 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.