Shrimp farming is an extremely important sector in food production worldwide, considering that the biggest problem they face are disease outbreaks. Various infections are attributed to the Vibrio genus, which cause significant mortality from the first days of cultivation, eventually eliminating up to 100% of the population. Within this genus there are specific species and strains that contain one or more extrachromosomal plasmids capable of encoding a potent binary t oxin (PirAB) that causes Acute Hepatopancreatic Necrosis Disease . The objective of this study was to determine the presence of toxigenic Vibrio parahaemolyticus in postlarvae of white shrimp collected in transport tanks of larval production laboratories, using bacteriological and molecular methods.
Samples were collected from a total of 26 containers, 12 corresponding to Sonora (LA, LC, LE) and 14 to Sinaloa (LB, LD, LF) between the months of April and July 2022 and February 2023.
Six of which test ed positive for toxigenic V. parahaemolyticus, corresponding to two laboratories. By the bacteriological method, 21 pos itive cases of toxigenic V. parahaemolyticus (green colonies, sucrose fermenters) were obtained. Using real-time PCR (IQ REAL AHPND/EMS Toxin 1 GeneReach) it was confirmed that six of the above cases were positive for the PirAB toxin. The partial region of the 16s rRNA of the positive bacterial strains was sequenced. In the BLAST system they were analyzed using the online algorithm and compared with the database reported in NCBI. Lab A presented V. campbellii and V. parahaemolyticus while Lab B presented V. campbellii.
The V. parahaemolyticus strain was known to be the main encoder of the binary toxin PirAB (Tran et al ., 2013). The plasmid encoding the binary toxin can be transferred between clades with high similarity. Horizontal gene transfer promotes the conversion of non-pathogenic strains into strains that increase the spread of AHPND (Han et al ., 2015; Restrepo et al ., 2018). This results in V. campbellii being reported as toxigenic strains carrying the binary toxin.
It was possible to diagnose the presence of the PirAB toxin in strains of the genus Vibrio , obtaining characteristics of typical colonies in TCBS and CRHOMagar media. Furthermore, the molecular identification used has high affinity with V. parahaemolyticus and V. campbellii.