Vibrio parahaemolyticus was isolated from shrimp of five farms located in the Pattani and Songkhla provinces of southern Thailand. Using a PCR method targeted to the unique DNA sequences derived from the plasmid (AP2 primers) and the toxin gene (AP3 primers) of V. parahaemolyticus that caused acute hepatopancreatic necrosis disease (AHPND), a total of 33 of 108 isolates were positive. In contrast, all 63 and 66 isolates of clinical and environmental V. parahaemolyticus, respectively, obtained previously from 2008 to 2014 from the same area were negative. This implied that these strains were likely to be the cause of the outbreak of AHPND in this area. Intestinal samples proved to be a better source for the isolation of V. parahaemolyticus AHPND than the hepatopancreas. All isolates were investigated for haemolytic activity, virulence genes, serotypes, genotypes and antibiotic susceptibility. All the AHPND isolates had a unique O antigen, but small variations of the K antigens were detected from different farms. In addition, the DNA profiles of V. parahaemolyticus AHPND isolates were similar, but distinct from those clinical and environmental isolates. It is postulated that the causative agent of AHPND might have originated from one clone and then slightly different serotypes subsequently developed.

Acute hepatopancreatic necrosis disease, a severe disease of shrimp, is caused by Vibrio parahaemolyticus (AHPND Vp), a halophilic bacterium harboring a plasmid that contains toxin genes homologous to Photorhabdus insect-related toxins. We obtained 9 isolates of Bdellovibrio and like organisms (BALOs) from water and sediment samples in Thailand. Using 16S rRNA sequencing, all of the organisms were identified as Bacteriovorax spp. and were able to attack all tested AHPND Vp isolates. In addition, their various susceptible hosts, including Gram-positive and Gram-negative bacteria, were observed. The optimal ratio for interaction between the Bacteriovorax isolate BV-A and AHPND Vp was determined to be 1:10. The suitable conditions applied for co-culture between BV-A and AHPND Vp were 30°C, 2% NaCl, and pH 7.6. The capability of BV-A to reduce numbers of AHPND Vp in vitro was observed in co-culture after incubation for 2 d and continued until the end of the incubation period. In vivo, BV-A was able to reduce mortality of shrimp post-larvae infected with AHPND Vp. In addition, BV-A significantly decreased the formation of biofilm by AHPND Vp. These findings provide evidence for using Bacteriovorax as a biocontrol of AHPND Vp in shrimp aquaculture.

BackgroundVibrio parahaemolyticus is a causative agent of gastroenteritis. Most of the clinical isolates carry either tdh and/or trh genes which are considered as the major virulence genes of this pathogen. In this study, the clinical isolates of V. parahaemolyticus carrying trh gene (n = 73) obtained from 1886 to 2012 from various countries were investigated for the urease production, haemolytic activity, and biofilm formation. In addition, the potential of clustered regularly interspaced short palindromic repeats (CRISPR)-based genotyping among these isolates was investigated.ResultsIn this study, no significant differences were observed in the urease production between tdh+ trh1+ and tdh+ trh2+ isolates (p = 0.063) and between the tdh− trh1+ and tdh− trh2+ isolates (p = 0.788). The isolates carrying only the trh gene showed variation in their haemolytic activity. The ratio of urease production and haemolytic activity between the trh1+ and trh2+ isolates and biofilm formation of trh+ V. parahaemolyticus isolates were not significantly different. Sixteen of thirty-four tested isolates (47.0%) of trh+ V. parahaemolyticus were positive for CRISPR detection. The discriminatory power index (DI) of CRISPR-virulence typing was higher than the DI obtained by CRISPR typing alone.ConclusionThe tdh and trh genes were not involved in urease production in the trh+ V. parahaemolyticus, and variation of haemolytic activity detected in V. parahaemolyticus carrying only the trh gene might be correlated to the sequence variation within trh1 and trh2 genes. Additionally, biofilm production of V. parahaemolyticus was not associated with harboring of virulence genes. For genotyping, CRISPR sequences combined with virulence genes can be used as genetic markers to differentiate trh+ V. parahaemolyticus strains.Electronic supplementary materialThe online version of this article (10.1186/s13099-018-0275-4) contains supplementary material, which is available to authorized users.

Vibrio parahaemolyticus is the causative agent of acute hepatopancreatic necrosis disease. In this study, we isolated yeasts possessing inhibitory activity against V. parahaemolyticus. In general, the generation time of yeasts is longer than that of bacteria. Therefore, the techniques used to evaluate yeasts with activity against bacteria using the same incubation time may not be appropriate. In this work, an agar well diffusion technique was modified to resolve this problem. Various selected yeast colonies were selected and each colony was introduced into an agar plug and incubated for 48 hr at room temperature. V. parahaemolyticus was spread onto Mueller Hinton agar plates, after agar plugs were removed to form wells and replaced with agar plugs seeded with yeast. After incubating for 24 hr at room temperature, the diameter of the inhibition zone was recorded. A total of 22 yeast isolates exhibited inhibitory activity towards V. parahaemolyticus. Thirteen isolates that possessed high inhibitory activity were identified by PCR and confirmed by sequencing, with four genera and 11 species of yeast identified. In a Galleria mellonella larvae model, a selected yeast strain reduced the larval mortality rate after being challenged with V. parahaemolyticus, indicating the usefulness of this yeast in shrimp aquaculture.