Background Acute hepatopancreatic necrosis syndrome (AHPND) caused by Vibrio parahaemolyticus strain (VPAHPND) impacts the shrimp industry worldwide. With the increasing problem of antibiotic abuse, studies on quorum sensing (QS) system and anti-QS compounds bring potential breakthroughs for disease prevention and treatment. Methods In this study, the cell-free culture supernatant (CFCS) and its extract of V. alginolyticus BC25 were investigated for anti-QS activity against a reporter bacteria, Chromobacterium violaceum DMST46846. The effects of CFCS and/ or extract on motility, biofilm formation and extracellular polymeric substances (EPSs) of VPAHPND PSU5591 were evaluated. Moreover, the effects of V. alginolyticus BC25 on virulence of VPAHPND PSU5591 were investigated by shrimp challenge test. The potentially active anti-QS compounds presented in the extract and effect on gene expression of VPAHPND PSU5591 were identified. Results The CFCS of V. alginolyticus BC25 and its extract showed a significant anti-QS activity against the reporter bacteria as well as swimming and swarming motilities, biofilms, and EPSs production by VPAHPND PSU5591. Transcriptome analysis revealed that V. alginolyticus BC25 extract significantly reduced the flagella genes involved in biofilm formation and iron-controlled virulence regulatory gene of VPAHPND PSU5591. Whereas, the LuxR family transcriptional regulator gene, c-factor, a cell-cell signaling gene, and capsular polysaccharide were up-regulated. The potentially active anti-QS compounds identified in extract were Cyclo-(L-Leu-L-Pro), and Cyclo-(L-Phe-L-Pro). Furthermore, V. alginolyticus BC25 enhanced disease resistance against VPAHPND PSU5591 in tested shrimp larvae. Conclusion These findings suggest that V. alginolyticus BC25 could provide natural anti-QS and anti-biofilms compounds and has great ability to be used as biocontrol agent against VPAHPND infection in shrimp aquaculture.
Acute hepatopancreatic necrosis syndrome (AHPND) caused by a unique Vibrio parahaemolyticus strain (VPAHPND) has emerged as a serious disease of cultured shrimps and is causing great economic losses worldwide. In this work, the effects of indole on quorum sensing‐dependent (QS) phenotypes of VPAHPND were assessed. In QS‐inhibitory bioassay using biomonitor strains, indole could interfere with N‐acyl homoserine lactones (AHL)‐mediated violacein pigment production of Chromobacterium violaceum, and autoinducer‐1 (AI‐1) and autoinducer‐2 (AI‐2)‐mediated QS response (bioluminescence) in V. campbellii. Further testing of indole with VPAHPND demonstrated significant decrease in the swimming and swarming motilities. In addition, VPAHPND grown in the presence of indole exhibited a reduction in biofilm formation, extracellular polymeric substances (EPSs) production and autoaggregation index. However, indole did not affect the ability of VPAHPND to use ferrous sulphate (FeSO4) as an iron source. Interestingly, indole reduced the expression of pirA (~2 fold), pirB (~2 fold), cpsA (~1.5 fold) and scrA (~1.7 fold) resulting in the reduction of toxin and capsule production. Lastly, indole‐treated VPAHPND exhibited lower virulence towards an infected model and its specific host, Galleria mellonella larvae and Litopenaeus vannamei respectively. These demonstrated the effects of indole in reducing multiple QS‐dependent phenotypes and virulence of VPAHPND. Thus, using indole, indole‐containing compounds, or indole‐producing organisms might be an attractive anti‐virulence strategy to control infections caused by VPAHPND.
Piper betle L. leaves have traditionally been used to treat various infectious diseases and to possess a wide spectrum of pharmacological effects. This study aimed to determine the antibacterial activity of the Piper betle leaf extract against antibiotic resistant Salmonella spp. isolated from pig farms located in Southern Thailand. Of this, 12 Salmonella spp. isolates were isolated from 24 pig fecal samples from 24 pig farms. The isolates were resistant to ampicillin (91.67%), penicillin (91.67%), tetracycline (81.81%), and doxycycline (81.81%). Antibacterial activity of the Piper betle ethanolic leaf extract against Salmonella spp. was carried out by disc diffusion assays, followed by Minimal inhibitory concentration (MIC) and Minimal bactericidal concentration (MBC) determination, as well as Time kill study. Piper betle extract exhibited antibacterial activity against all the isolates and S. Typhimurium with the inhibition zone ranged from 15.11 ± 0.34 to 20.30 ± 0.50 mm as observed by disc diffusion assay. The extract showed bactericidal activity against the isolates with the MIC and MBC values ranging from 0.5-1.0 mg/mL. Furthermore, the extract at 4 × MIC showed the killing activity with the reduction of the pathogen at least 3 logs within 8 h. The information suggests potential medicinal benefits of the Piper betle leaf extract to inhibit the growth of antibiotic resistant Salmonella spp. isolated from pig farms.
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