Abstract
Objective: This study was done to report the results of genetic diversity and toxic genes analysis of Vibrio pathogen isolated from white leg shrimp and marine fishes cultured in Thua Thien Hue province, Vietnam. Methods/statistical analysis: Pathogen Vibrio spp. were isolated from shrimps and fishes, and were identified by 16S rRNA sequencing. The presence of toxin genes in Vibrio spp. strains were determined through the presence of genes encoding toxic proteins (pirAvp, pir-Bvp, tlh, tdh and trh) based on specific primers for these genes. Genetic diversity of Vibrio strains was analysed by RAPD technique. Findings: A total of 120 Vibrio colonies from shrimps (with Acute Hepatopancreatic Necrosis Disease) and fishes (with hemorrhagic disease) cultured in Tam Giang lagoon in Thua Thien Hue, Vietnam were isolated. Of which, 14/54 strains from shrimps had pirAvp and pirBvp genes and 18/66 strains from fishes had tlh gene, and none of Vibrio strains had tdh and trh genes. Randomly amplified polymorphic DNA (RAPD) analysis of 36 Vibrio samples showed the 148 polymorphic DNA fragments from ten random primers. The genetic diversity is high within studied species. In there, V. parahaemolyticus has the highest diversity level (h=0.1645 and I=0.2695) while V. shilonii is lowest (h=0.0136) and I=0.0207). The degree of genetic differentiation among species is also high (Gst=0.4827). Genetic identity between V. parahaemolyticus and V. vulnificus (0.9545) is highest while between V. shilonii and V. harveyi (0.7416) is lowest. The dendrogram also showed that V. parahaemolyticus is closely related to V. vulnificus whereas V. shilonii and V. harveyi have large distance. Application/improvements: This study is aimed to provide scientific data as the basis for the study and production of rapid diagnostic kits in the future. Keywords: AHPND; Genetic diversity; RAPD; toxic genes; Vibrio; Vietnam
Highlights
Vibrio spp. are found in all over the world in marine and estuarine environments
From 120 Vibrio samples, we found that 14 strains and 18 strains had pirAvp and pirBvp genes or tlh gene, respectively ( Tables 2 and 3)
The pVPA3-1 plasmid causes Acute Hepatopancreatic Necrosis Disease (AHPND) was identified in V. parahaemolyticus strain 13-028/A3, it consists of genes that encode mobilization proteins, replication enzymes, virulence-associated proteins, and proteins similar to Photorhabdus insect-related (Pir) toxins
Summary
Vibrio spp. are found in all over the world in marine and estuarine environments. In fish, this genus is present as a part of the normal intestinal microflora. Acute Hepatopancreatic Necrosis Disease (AHPND) has caused remarkable mortality (up to 100%) in populations of shrimp cultured in South East Asian and Latin American countries. This disease is referred to as early mortality syndrome (EMS). AHPND is caused by several Vibrio species, which secretes proteins similar to Photorhabdus insect-related (Pir) toxins (PirAvp and PirBvp)(1,2). Vibrio spp. are mainly pathogenic to brackish water and marine fish. The distribution of vibriosis is worldwide and causes economic loss to the aquaculture industry [3]
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