Detection of ctx gene positive non-O1/non-O139 V. cholerae in shrimp aquaculture environments

Abstract

Water and post-larvae samples from black tiger (Penaeus monodon) shrimp hatcheries; pond water, pond sediment and shrimp from aquaculture farms were screened for the presence of V. cholerae. A V. cholerae-duplex PCR method was developed by utilizing V. cholerae species specific sodB primers and ctxAB genes specific primers. Incidence of V. cholerae was not observed in shrimp hatchery samples but was noticed in aquaculture samples. The incidence of V. cholerae was higher in pond water (7.6%) than in pond sediment (5.2%). Shrimp head (3.6%) portion had relatively higher incidence than shrimp muscle (1.6%). All the V. cholerae isolates (n = 42) belonged to non-O1/non-O139 serogroup, of which 7% of the V. cholerae isolates were potentially cholera-toxigenic (ctx positive). All the ctx positive V. cholerae (n = 3) were isolated from the pond water. Since, cholera toxin (CT) is the major contributing factor for cholera gravis, it is proposed that the mere presence of non-O1/non-O139 V. cholerae need not be the biohazard criterion in cultured black tiger shrimp but only the presence of ctx carrying non-O1/non-O139 V. cholerae may be considered as potential public health risk.