In this study, we investigated the impact of the host factors mucin, bile salts and cholesterol o... more In this study, we investigated the impact of the host factors mucin, bile salts and cholesterol on the virulence of the economically important aquatic pathogen Vibrio anguillarum towards sea bass larvae. Pretreatment of V. anguillarum with either one of the host factors (at 10 mg l(-1)) prior to inoculation into the sea bass rearing water increased virulence of the bacterium, although the effect of cholesterol was not significant. Each of the three host factors significantly increased several virulence-related phenotypes in V. anguillarum, i.e. protease activity, flagellar motility, biofilm formation and exopolysaccharide production, whereas there was no effect on growth of the bacterium under these conditions. Furthermore, the host factors increased the expression of genes involved in these phenotypes, i.e. the metalloprotease empA, the flagellar transcriptional regulator fleQ, the flagellin gene flaA, the chemotaxis methyltransferase gene cheR, the exopolysaccharide biosynthesis g...
Quorum sensing, bacterial cell-to-cell communication with small signal molecules, controls the vi... more Quorum sensing, bacterial cell-to-cell communication with small signal molecules, controls the virulence of many pathogens. In contrast to other vibrios, neither the VanI/VanR acylhomoserine lactone quorum sensing system, nor the three-channel quorum sensing system affects virulence of the economically important aquatic pathogen Vibrio anguillarum. Indole is another molecule that recently gained attention as a putative signal molecule. The data presented in this study indicate that indole signaling and the alternative sigma factor RpoS have a significant impact on the virulence of V. anguillarum. Deletion of rpoS resulted in increased expression of the indole biosynthesis gene tnaA and in increased production of indole. Both rpoS deletion and the addition of exogenous indole (50-100 mM) resulted in decreased biofilm formation, exopolysaccharide production (a phenotype that is required for pathogenicity) and expression of the exopolysaccharide synthesis gene wbfD. Further, indole inhibitors increased the virulence of the rpoS deletion mutant, suggesting that indole acts downstream of RpoS. Finally, in addition to the phenotypes found to be affected by indole, the rpoS deletion mutant also showed increased motility and decreased sensitivity to oxidative stress. Citation: Li X, Yang Q, Dierckens K, Milton DL, Defoirdt T (2014) RpoS and Indole Signaling Control the Virulence of Vibrio anguillarum towards Gnotobiotic Sea Bass (Dicentrarchus labrax) Larvae. PLoS ONE 9(10): e111801.
Homoserine lactone-degrading and poly-β-hydroxybutyrate-accumulating enrichment cultures (ECs) we... more Homoserine lactone-degrading and poly-β-hydroxybutyrate-accumulating enrichment cultures (ECs) were obtained using glycerol as C-source and homoserine lactones as N-source, at a high C/N ratio (78). The kinetics of acyl homoserine lactone (AHL) degradation was established and the poly-β-hydroxybutyrate (PHB) content of the obtained ECs was determined. The ECs were characterised through denaturing gradient gel electrophoresis (DGGE) and the main bands were genetically identified by sequence analysis. In a Vibrio challenge test using Artemia as target organism, a distinct difference in survival of challenged Artemia between the treatments with and without the presence of ECs was observed (53% ± 6; 69% ± 5 and 58% ± 8 versus 4% ± 5; 4% ± 5 and 25% ± 21) in three independent experiments. There was a strong positive correlation between the relative percentage survival values of Artemia and the AHL degradation rate and the PHB content of the ECs. Challenge data with a quorum sensing mutant suggested that the quorum quenching ability of the ECs was less relevant in this Artemia model system, pointing to the importance of PHB. The potential of growing these beneficial ECs on glycerol released into the hatching medium of Artemia was an asset that still requires validation at hatchery level.
Infections caused by antibiotic-resistant luminescent Vibrios can cause dramatic losses in aquacu... more Infections caused by antibiotic-resistant luminescent Vibrios can cause dramatic losses in aquaculture. In this study, the short-chain fatty acid beta-hydroxybutyrate and its polymer poly-beta-hydroxybutyrate were investigated as possible new biocontrol agents. beta-Hydroxybutyrate was shown to completely inhibit the growth of pathogenic Vibrio campbelli at 100 mM. Moreover, the addition of 100 mM of this fatty acid to the culture water of Artemia nauplii infected with the V. campbelli strain significantly increased the survival of the nauplii. As Artemia is a non-selective and particle filter feeder, we also investigated whether poly-beta-hydroxybutyrate particles could be used to protect Artemia from the pathogenic V. campbellii. The addition of 100 mg l(-1) poly-beta-hydroxybutyrate or more to the Artemia culture water offered a preventive and curative protection from the pathogen as a significantly enhanced survival was noticed. If added as a preventive treatment, a complete pro...
... England. Other Details: Languages: eng Pagination: 36 Citation Subset: IM. Affiliation: Depar... more ... England. Other Details: Languages: eng Pagination: 36 Citation Subset: IM. Affiliation: Department of Medical Microbiology and Infection Control, Jeroen Bosch Hospital,'s-Hertogenbosh, The Netherlands. [email protected]. ...
Vlaams Instituut voor de Zee. VLIZ. Informatie over marien en kustgebonden onderzoek & be... more Vlaams Instituut voor de Zee. VLIZ. Informatie over marien en kustgebonden onderzoek & beleid in Vlaanderen.
Infections caused by antibiotic-resistant pathogenic bacteria can cause considerable losses in aq... more Infections caused by antibiotic-resistant pathogenic bacteria can cause considerable losses in aquaculture. Many aquaculture pathogens regulate the expression of virulence genes through quorum sensing, bacterial cell-to-cell communication with small signal molecules. N-acyl homoserine lactones (AHLs) are the most extensively studied class of quorum sensing signals. AHL-degrading enrichment cultures were previously isolated from the intestinal tract of healthy aquaculture animals and found to increase the survival of fish and shrimp larvae. In this study, we isolated Gram-positive spore-forming strains from AHL-degrading enrichment cultures originating from whiteleg shrimp and European sea bass. Five selected isolates showed good AHL degradation abilities in a nutrient-rich background, simulating the presence of high levels of other nutrients as is the case in a gastrointestinal environment. Indeed, degradation rates between 0.7 and 0.9 mg l − 1 h − 1 were observed in Luria-Bertani medium supplemented with 5 mg l − 1 N-hexanoyl-L-homoserine lactone. The selected isolates were confirmed to belong to the genus Bacillus by 16S rDNA sequencing and might be interesting novel biocontrol strains for use in aquaculture.
Vibrios belonging to the Harveyi clade are important pathogens of a large number of marine animal... more Vibrios belonging to the Harveyi clade are important pathogens of a large number of marine animals in the aquaculture industry. In this study, six isolates (H1 to H6) were obtained from a shrimp hatchery in Rio Grande do Norte (Natal-Area, Brazil), which had been confronted with disease outbreaks in 2009. The aim was to characterize the virulence of these isolates, both in vitro (virulence factor production) and in vivo (virulence towards gnotobiotic brine shrimp, Artemia franciscana, larvae) and to compare these characteristics to those of the most virulent pathogen in the brine shrimp model described to date, Vibrio campbellii LMG 21363. Of all 6 isolates, H5 and H6 were found to be the most virulent ones and were therefore selected for further characterization. Isolate H5 exhibited a similar virulence as the control strain, while H6 exhibited a higher virulence, both in gnotobiotic and conventionally reared brine shrimp. Both H5 and H6 were motile and produced all of the lytic enzymes tested (hemolysin, caseinase, gelatinase, lipase and phospholipase). Although H6 was the most virulent isolate in vivo, this was not reflected in the highest production of all virulence factors tested. Finally, isolates H5 and H6 were identified to belong to the Harveyi clade of vibrios.
Obtaining a better understanding of mechanisms involved in bacterial infections is of paramount i... more Obtaining a better understanding of mechanisms involved in bacterial infections is of paramount importance for the development of novel agents to control disease caused by (antibiotic resistant) pathogens in aquaculture. In this study, we investigated the impact of catecholamine stress hormones on growth and virulence factor production of pathogenic vibrios (i.e. two Vibrio campbellii strains and two Vibrio anguillarum strains). Both norepinephrine and dopamine (at 100 lM) significantly induced growth in media containing serum. The compounds also increased swimming motility of the tested strains, whereas they had no effect on caseinase, chitinase, and hemolysin activities. Further, antagonists for eukaryotic catecholamine receptors were able to neutralize some of the effects of the catecholamines. Indeed, the dopaminergic receptor antagonist chlorpromazine neutralized the effect of dopamine, and the a-adrenergic receptor antagonists phentolamine and phenoxybenzamine neutralized the effect of norepinephrine, whereas the b-adrenergic receptor antagonist propranolol had limited to no effect. Finally, pretreatment of pathogenic V. campbellii with catecholamines significantly increased its virulence toward giant freshwater prawn larvae. However, the impact of catecholamine receptor antagonists on in vivo virulence was less clear-cut when compared to the in vitro experiments. In summary, our results show thatsimilar to enteric pathogens catecholamines also increase the virulence of vibrios that are pathogenic to aquatic organisms by increasing motility and growth in media containing serum.
In this study, we investigated the impact of the host factors mucin, bile salts and cholesterol o... more In this study, we investigated the impact of the host factors mucin, bile salts and cholesterol on the virulence of the economically important aquatic pathogen Vibrio anguillarum towards sea bass larvae. Pretreatment of V. anguillarum with either one of the host factors (at 10 mg l(-1)) prior to inoculation into the sea bass rearing water increased virulence of the bacterium, although the effect of cholesterol was not significant. Each of the three host factors significantly increased several virulence-related phenotypes in V. anguillarum, i.e. protease activity, flagellar motility, biofilm formation and exopolysaccharide production, whereas there was no effect on growth of the bacterium under these conditions. Furthermore, the host factors increased the expression of genes involved in these phenotypes, i.e. the metalloprotease empA, the flagellar transcriptional regulator fleQ, the flagellin gene flaA, the chemotaxis methyltransferase gene cheR, the exopolysaccharide biosynthesis g...
Quorum sensing, bacterial cell-to-cell communication with small signal molecules, controls the vi... more Quorum sensing, bacterial cell-to-cell communication with small signal molecules, controls the virulence of many pathogens. In contrast to other vibrios, neither the VanI/VanR acylhomoserine lactone quorum sensing system, nor the three-channel quorum sensing system affects virulence of the economically important aquatic pathogen Vibrio anguillarum. Indole is another molecule that recently gained attention as a putative signal molecule. The data presented in this study indicate that indole signaling and the alternative sigma factor RpoS have a significant impact on the virulence of V. anguillarum. Deletion of rpoS resulted in increased expression of the indole biosynthesis gene tnaA and in increased production of indole. Both rpoS deletion and the addition of exogenous indole (50-100 mM) resulted in decreased biofilm formation, exopolysaccharide production (a phenotype that is required for pathogenicity) and expression of the exopolysaccharide synthesis gene wbfD. Further, indole inhibitors increased the virulence of the rpoS deletion mutant, suggesting that indole acts downstream of RpoS. Finally, in addition to the phenotypes found to be affected by indole, the rpoS deletion mutant also showed increased motility and decreased sensitivity to oxidative stress. Citation: Li X, Yang Q, Dierckens K, Milton DL, Defoirdt T (2014) RpoS and Indole Signaling Control the Virulence of Vibrio anguillarum towards Gnotobiotic Sea Bass (Dicentrarchus labrax) Larvae. PLoS ONE 9(10): e111801.
Homoserine lactone-degrading and poly-β-hydroxybutyrate-accumulating enrichment cultures (ECs) we... more Homoserine lactone-degrading and poly-β-hydroxybutyrate-accumulating enrichment cultures (ECs) were obtained using glycerol as C-source and homoserine lactones as N-source, at a high C/N ratio (78). The kinetics of acyl homoserine lactone (AHL) degradation was established and the poly-β-hydroxybutyrate (PHB) content of the obtained ECs was determined. The ECs were characterised through denaturing gradient gel electrophoresis (DGGE) and the main bands were genetically identified by sequence analysis. In a Vibrio challenge test using Artemia as target organism, a distinct difference in survival of challenged Artemia between the treatments with and without the presence of ECs was observed (53% ± 6; 69% ± 5 and 58% ± 8 versus 4% ± 5; 4% ± 5 and 25% ± 21) in three independent experiments. There was a strong positive correlation between the relative percentage survival values of Artemia and the AHL degradation rate and the PHB content of the ECs. Challenge data with a quorum sensing mutant suggested that the quorum quenching ability of the ECs was less relevant in this Artemia model system, pointing to the importance of PHB. The potential of growing these beneficial ECs on glycerol released into the hatching medium of Artemia was an asset that still requires validation at hatchery level.
Infections caused by antibiotic-resistant luminescent Vibrios can cause dramatic losses in aquacu... more Infections caused by antibiotic-resistant luminescent Vibrios can cause dramatic losses in aquaculture. In this study, the short-chain fatty acid beta-hydroxybutyrate and its polymer poly-beta-hydroxybutyrate were investigated as possible new biocontrol agents. beta-Hydroxybutyrate was shown to completely inhibit the growth of pathogenic Vibrio campbelli at 100 mM. Moreover, the addition of 100 mM of this fatty acid to the culture water of Artemia nauplii infected with the V. campbelli strain significantly increased the survival of the nauplii. As Artemia is a non-selective and particle filter feeder, we also investigated whether poly-beta-hydroxybutyrate particles could be used to protect Artemia from the pathogenic V. campbellii. The addition of 100 mg l(-1) poly-beta-hydroxybutyrate or more to the Artemia culture water offered a preventive and curative protection from the pathogen as a significantly enhanced survival was noticed. If added as a preventive treatment, a complete pro...
... England. Other Details: Languages: eng Pagination: 36 Citation Subset: IM. Affiliation: Depar... more ... England. Other Details: Languages: eng Pagination: 36 Citation Subset: IM. Affiliation: Department of Medical Microbiology and Infection Control, Jeroen Bosch Hospital,'s-Hertogenbosh, The Netherlands. [email protected]. ...
Vlaams Instituut voor de Zee. VLIZ. Informatie over marien en kustgebonden onderzoek & be... more Vlaams Instituut voor de Zee. VLIZ. Informatie over marien en kustgebonden onderzoek & beleid in Vlaanderen.
Infections caused by antibiotic-resistant pathogenic bacteria can cause considerable losses in aq... more Infections caused by antibiotic-resistant pathogenic bacteria can cause considerable losses in aquaculture. Many aquaculture pathogens regulate the expression of virulence genes through quorum sensing, bacterial cell-to-cell communication with small signal molecules. N-acyl homoserine lactones (AHLs) are the most extensively studied class of quorum sensing signals. AHL-degrading enrichment cultures were previously isolated from the intestinal tract of healthy aquaculture animals and found to increase the survival of fish and shrimp larvae. In this study, we isolated Gram-positive spore-forming strains from AHL-degrading enrichment cultures originating from whiteleg shrimp and European sea bass. Five selected isolates showed good AHL degradation abilities in a nutrient-rich background, simulating the presence of high levels of other nutrients as is the case in a gastrointestinal environment. Indeed, degradation rates between 0.7 and 0.9 mg l − 1 h − 1 were observed in Luria-Bertani medium supplemented with 5 mg l − 1 N-hexanoyl-L-homoserine lactone. The selected isolates were confirmed to belong to the genus Bacillus by 16S rDNA sequencing and might be interesting novel biocontrol strains for use in aquaculture.
Vibrios belonging to the Harveyi clade are important pathogens of a large number of marine animal... more Vibrios belonging to the Harveyi clade are important pathogens of a large number of marine animals in the aquaculture industry. In this study, six isolates (H1 to H6) were obtained from a shrimp hatchery in Rio Grande do Norte (Natal-Area, Brazil), which had been confronted with disease outbreaks in 2009. The aim was to characterize the virulence of these isolates, both in vitro (virulence factor production) and in vivo (virulence towards gnotobiotic brine shrimp, Artemia franciscana, larvae) and to compare these characteristics to those of the most virulent pathogen in the brine shrimp model described to date, Vibrio campbellii LMG 21363. Of all 6 isolates, H5 and H6 were found to be the most virulent ones and were therefore selected for further characterization. Isolate H5 exhibited a similar virulence as the control strain, while H6 exhibited a higher virulence, both in gnotobiotic and conventionally reared brine shrimp. Both H5 and H6 were motile and produced all of the lytic enzymes tested (hemolysin, caseinase, gelatinase, lipase and phospholipase). Although H6 was the most virulent isolate in vivo, this was not reflected in the highest production of all virulence factors tested. Finally, isolates H5 and H6 were identified to belong to the Harveyi clade of vibrios.
Obtaining a better understanding of mechanisms involved in bacterial infections is of paramount i... more Obtaining a better understanding of mechanisms involved in bacterial infections is of paramount importance for the development of novel agents to control disease caused by (antibiotic resistant) pathogens in aquaculture. In this study, we investigated the impact of catecholamine stress hormones on growth and virulence factor production of pathogenic vibrios (i.e. two Vibrio campbellii strains and two Vibrio anguillarum strains). Both norepinephrine and dopamine (at 100 lM) significantly induced growth in media containing serum. The compounds also increased swimming motility of the tested strains, whereas they had no effect on caseinase, chitinase, and hemolysin activities. Further, antagonists for eukaryotic catecholamine receptors were able to neutralize some of the effects of the catecholamines. Indeed, the dopaminergic receptor antagonist chlorpromazine neutralized the effect of dopamine, and the a-adrenergic receptor antagonists phentolamine and phenoxybenzamine neutralized the effect of norepinephrine, whereas the b-adrenergic receptor antagonist propranolol had limited to no effect. Finally, pretreatment of pathogenic V. campbellii with catecholamines significantly increased its virulence toward giant freshwater prawn larvae. However, the impact of catecholamine receptor antagonists on in vivo virulence was less clear-cut when compared to the in vitro experiments. In summary, our results show thatsimilar to enteric pathogens catecholamines also increase the virulence of vibrios that are pathogenic to aquatic organisms by increasing motility and growth in media containing serum.
Uploads
Papers by Tom Defoirdt