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Daniel L Merrifield - One of the best experts on this subject based on the ideXlab platform.
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dietary probiotic Pediococcus acidilactici ma18 5m modulates the intestinal microbiota and stimulates intestinal immunity in rainbow trout oncorhynchus mykiss
Journal of The World Aquaculture Society, 2019Co-Authors: Ali Alhisnawi, Mathieu Castex, Oliana Carnevali, Mark D Rawling, Ana Rodiles, Paul Waines, Georgia Gioacchini, Daniel L MerrifieldAbstract:A study was conducted to evaluate the probiotic effect of Pediococcus acidilactici MA18/5M on rainbow trout, Oncorhynchus mykiss. Fish (310 ± 9 g) were fed a control diet or a P. acidilactici‐supplemented diet (at 2.4 × 10⁶ CFU/g) for 4 weeks. The probiotic was observed to populate the intestine with levels ranging from log 3.7 to 5.4 CFU/g. Furthermore, these populations were able to persist for at least 24 hr after the cessation of probiotic feeding. High‐throughput sequencing analysis of bacterial 16S rRNA libraries demonstrated that P. acidilactici was able to modulate the gut microbiome of rainbow trout and that the probiotic was detected as a common taxon on the mucosa and in the digesta of the probiotic fish (p < .05). Real‐time polymerase chain reaction demonstrated that feeding the probiotic upregulated pro‐inflammatory cytokines, interleukin‐1β, and interleukin‐8 and downregulated anti‐inflammatory interleukin‐10 compared to the control‐fed fish. Furthermore, the mRNA levels for the mucosal antibody immunoglobulin T was also elevated in probiotic‐fed fish. These findings help to explain some of the mechanisms behind the previously reported observed benefits of using this probiotic in the intestinal morphology and immunity of rainbow trout.
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probiotic Pediococcus acidilactici modulates both localised intestinal and peripheral immunity in tilapia oreochromis niloticus
Fish & Shellfish Immunology, 2013Co-Authors: Benedict Standen, Mathieu Castex, S J Davies, Andrew D Foey, Giorgia Gioacchini, Oliana Carnevali, Daniel L MerrifieldAbstract:The application of probiotics in aquaculture has received concerted research efforts but the localised intestinal immunological response of fish to probiotic bacteria is poorly understood. Therefore, a study was conducted to evaluate the probiotic effect of Pediococcus acidilactici on Nile tilapia (Oreochromis niloticus) with specific emphasis on intestinal health and probiotic levels as well as system level responses such as growth performance, feed utilization and haemato-immunological parameters under non-challenged conditions. Fish (9.19 ± 0.04 g) were fed either a control diet or a P. acidilactici supplemented diet (at 2.81 × 10(6) CFU g(-)(1)) for six weeks. At the end of the study the probiotic was observed to populate the intestine, accounting for ca. 3% (1.59 × 10(5) CFU g(-)(1)) of the cultivable intestinal bacterial load. Real-time PCR indicated that the probiotic treatment may potentiate the immune-responsiveness of the intestine as up-regulation of the gene expression of the pro-inflammatory cytokine TNFα was observed in the probiotic fed fish (P 0.05).
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probiotic Pediococcus acidilactici modulates both localised intestinal and peripheral immunity in tilapia oreochromis niloticus
Fish & Shellfish Immunology, 2013Co-Authors: Benedict Standen, Mathieu Castex, S J Davies, Andrew D Foey, Giorgia Gioacchini, Oliana Carnevali, Mark D Rawling, Daniel L MerrifieldAbstract:Abstract The application of probiotics in aquaculture has received concerted research efforts but the localised intestinal immunological response of fish to probiotic bacteria is poorly understood. Therefore, a study was conducted to evaluate the probiotic effect of Pediococcus acidilactici on Nile tilapia ( Oreochromis niloticus ) with specific emphasis on intestinal health and probiotic levels as well as system level responses such as growth performance, feed utilization and haemato-immunological parameters under non-challenged conditions. Fish (9.19 ± 0.04 g) were fed either a control diet or a P. acidilactici supplemented diet (at 2.81 × 10 6 CFU g − 1 ) for six weeks. At the end of the study the probiotic was observed to populate the intestine, accounting for ca. 3% (1.59 × 10 5 CFU g − 1 ) of the cultivable intestinal bacterial load. Real-time PCR indicated that the probiotic treatment may potentiate the immune-responsiveness of the intestine as up-regulation of the gene expression of the pro-inflammatory cytokine TNFα was observed in the probiotic fed fish ( P P. acidilactici fed tilapia after six weeks ( P P = 0.08). Concomitantly at week six, along with elevated IELs and elevated TNFα mRNA levels in the intestine, an increased abundance of circulating neutrophils and monocytes were observed in fish fed the probiotic supplemented diet ( P P > 0.05).
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the effect of Pediococcus acidilactici on the gut microbiota and immune status of on growing red tilapia oreochromis niloticus
Journal of Applied Microbiology, 2010Co-Authors: Robert M W Ferguson, Daniel L Merrifield, Mark D Rawling, Glenn M Harper, Sanaa A Mustafa, Simona Picchietti, Jose Luis Balcazar, S J DaviesAbstract:Aim: To assess Pediococcus acidilactici as a dietary supplement for on-growing red tilapia (Oreochromis niloticus). Methods and Results: Tilapia were fed either a control diet or control diet supplemented with Ped. acidilactici at 10 7 CFU g -1 for 32 days. Ped. acidilactici colonized the intestinal tract and significantly affected the intestinal microbial communities. PCR-DGGE revealed direct antagonism of gastric Ped. acidilactici with an endogenous uncultured bacterium during a period of reverting to nonsupplemented feeding. Light microscopy revealed that gut integrity and leucocyte levels were unaffec ted by Ped. acidilactici; however, blood leucocyte levels and serum lysozyme activity were elevated after 14-days' feeding. No significant improvements in growth performance were observed at the end of the trial (day 32), but survival was significantly higher in the probiotic group. Conclusions: The study demonstrates that oral supplementation of Ped. acidilactici modulates intestinal bacterial communities in on-growing red tilapia and also stimulates some aspects of the nonspecific immune response. Significance and Impact of the study: To our knowledge this is the first study assessing the effects of probiotics on the gut microbiota of tilapia using culture-independent methods. Such methods are crucial to understand the mechanisms which underpin and mediate host benefits. © 2010 The Society for Applied Microbiology.
Jie Bao - One of the best experts on this subject based on the ideXlab platform.
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optically pure lactic acid production from softwood derived mannose by Pediococcus acidilactici
Journal of Biotechnology, 2021Co-Authors: Joana Campos, Jie Bao, Gunnar LidenAbstract:Softwood is of interest as a renewable carbon source for production of lactic acid. Softwood hydrolysate contains a high content of mannose. Lactic acid production from mannose by two modified strains, L-lactic acid producing Pediococcus acidilactici TY112 and D-lactic acid producing ZP26, was investigated in the current work. The two strains efficiently converted mannose to L- and D-lactate isomers with an optical purity exceeding 99 %, although the mannose utilization rates were lower than the glucose utilization rates. The mannose conversion to L- and D-lactic acids by P. acidilactici was also confirmed in dilute spruce hemicellulose hydrolysate. The present study provides important knowledge on utilization of the spectrum of fermentable sugars in softwood for future production of chiral lactic acid from lignocellulose feedstocks.
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A short-chain dehydrogenase plays a key role in cellulosic D-lactic acid fermentability of Pediococcus acidilactici.
Bioresource technology, 2019Co-Authors: Zhongyang Qiu, Qiuqiang Gao, Chun Fang, Jie BaoAbstract:Abstract Phenolic aldehydes from lignocellulose pretreatment are strong inhibitors of cell growth and metabolism of cellulosic lactic acid bacteria. Their low solubility and recalcitrance highly reduce the removal efficiency of various detoxification methods. This study shows a simultaneous conversion of phenolic aldehydes and fermentation of D-lactic acid by Pediococcus acidilactici using corn stover feedstock. Vanillin was found to be the strongest phenolic aldehyde inhibitor to P. acidilactici. The overexpression of a short-chain dehydrogenase encoded by the gene CGS9114_RS09725 from Corynebacterium glutamicum was identified to play a key role in D-lactic acid fermentability of P. acidilactici. The engineered P. acidilactici with the genome integration of CGS9114_RS09725 showed the accelerated vanillin reduction and improved cellulosic D-lactic acid production. This study reveals that vanillin conversion is crucial for D-lactic acid fermentation, and the direct expression of a specific vanillin reduction gene in lactic acid bacterium efficiently improves cellulosic D-lactic acid production.
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Engineering Pediococcus acidilactici with xylose assimilation pathway for high titer cellulosic L-lactic acid fermentation
Bioresource Technology, 2018Co-Authors: Zhongyang Qiu, Qiuqiang Gao, Jie BaoAbstract:Xylose-assimilating pathways were constructed in the parental Pediococcus acidilactici strain and evolutionarily adapted to yield a highly stable co-fermentation strain for L-lactic acid production. The phosphoketolase pathway (PK) was blocked for reduction of acetic acid generation by disrupting phosphoketolase (pkt) gene. The pentose phosphate pathway (PPP) was reconstructed for xylose assimilation by integrating four heterologous genes encoding transketolase (tkt), transaldolase (tal), xylose isomerase (xylA) and xylulokinase (xylB) into the P. acidilactici chromosome. The xylose-assimilating ability of the constructed strain was significantly improved by long term adaptive evolution. The engineered strain was applied to the simultaneous saccharification and co-fermentation (SSCF) under high solids loading of wheat straw. The L-lactic acid titer, productivity and xylose conversion reached the record high at 130.8 ± 1.6 g/L, 1.82 ± 0.0 g/L/h, and 94.9 ± 0.0%, respectively. This study provided an important strain and process prototype for production of high titer cellulosic L-lactic acid.
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Constructing xylose-assimilating pathways in Pediococcus acidilactici for high titer D-lactic acid fermentation from corn stover feedstock
Bioresource Technology, 2017Co-Authors: Zhongyang Qiu, Qiuqiang Gao, Jie BaoAbstract:Xylose-assimilating pathway was constructed in a D-lactic acid producing Pediococcus acidilactici strain and evolutionary adapted to yield a co-fermentation strain P. acidilactici ZY15 with 97.3 g/L of D-lactic acid and xylose conversion of 92.6% obtained in the high solids content simultaneous saccharification and co-fermentation (SSCF) of dry dilute acid pretreated and biodetoxified corn stover feedstock. The heterologous genes encoding xylose isomerase (xylA) and xylulokinase (xylB) were screened and integrated into the P. acidilactici chromosome. The metabolic flux to acetic acid in phosphoketolase pathway was re-directed to pentose phosphate pathway by substituting the endogenous phosphoketolase gene (pkt) with the heterologous transketolase (tkt) and transaldolase (tal) genes. The xylose-assimilating ability of the newly constructed P. acidilactici strain was significantly improved by adaptive evolution. This study provided an important strain and process prototype for high titer D-lactic acid production from lignocellulose feedstock with efficient xylose assimilation.
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engineering wild type robust Pediococcus acidilactici strain for high titer l and d lactic acid production from corn stover feedstock
Journal of Biotechnology, 2016Co-Authors: Peng Zhang, Qiuqiang Gao, Jian Zhang, Jiaoe Sun, Jie BaoAbstract:Pediococcus acidilactici TY112 producing L-lactic acid and P. acidilactici ZP26 producing D-lactic acid, were engineered from the wild-type P. acidilactici DQ2 by ldhD or ldh gene disruption, and the robustness of the wild-type strain to the inhibitors derived from lignocellulose pretreatment was maintained well. In simultaneous saccharification and fermentation (SSF), 77.66 g L(-1) of L-lactic acid and 76.76 g L(-1) of D-lactic acid were obtained at 25% (w/w) solids content of dry dilute acid pretreated and biodetoxified corn stover feedstock. L- and D-Lactic acid yield and productivity were highly dependent on the inhibitor removal extent due to the significant down-regulation on the expressions of ldh and ldhD encoding lactate dehydrogenase by inhibitor, especially syringaldehyde and vanillin at the low concentrations. This study provided a prototype of industrial process for high titer L- and D-lactic acid production from lignocellulose feedstock.
Mathieu Castex - One of the best experts on this subject based on the ideXlab platform.
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dietary probiotic Pediococcus acidilactici ma18 5m modulates the intestinal microbiota and stimulates intestinal immunity in rainbow trout oncorhynchus mykiss
Journal of The World Aquaculture Society, 2019Co-Authors: Ali Alhisnawi, Mathieu Castex, Oliana Carnevali, Mark D Rawling, Ana Rodiles, Paul Waines, Georgia Gioacchini, Daniel L MerrifieldAbstract:A study was conducted to evaluate the probiotic effect of Pediococcus acidilactici MA18/5M on rainbow trout, Oncorhynchus mykiss. Fish (310 ± 9 g) were fed a control diet or a P. acidilactici‐supplemented diet (at 2.4 × 10⁶ CFU/g) for 4 weeks. The probiotic was observed to populate the intestine with levels ranging from log 3.7 to 5.4 CFU/g. Furthermore, these populations were able to persist for at least 24 hr after the cessation of probiotic feeding. High‐throughput sequencing analysis of bacterial 16S rRNA libraries demonstrated that P. acidilactici was able to modulate the gut microbiome of rainbow trout and that the probiotic was detected as a common taxon on the mucosa and in the digesta of the probiotic fish (p < .05). Real‐time polymerase chain reaction demonstrated that feeding the probiotic upregulated pro‐inflammatory cytokines, interleukin‐1β, and interleukin‐8 and downregulated anti‐inflammatory interleukin‐10 compared to the control‐fed fish. Furthermore, the mRNA levels for the mucosal antibody immunoglobulin T was also elevated in probiotic‐fed fish. These findings help to explain some of the mechanisms behind the previously reported observed benefits of using this probiotic in the intestinal morphology and immunity of rainbow trout.
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effects of dietary supplementation with Pediococcus acidilactici ma18 5m galactooligosaccharide and their synbiotic on growth innate immunity and disease resistance of rockfish sebastes schlegeli
Aquaculture, 2018Co-Authors: Samad Rahimnejad, Francisco A Guardiola, Eric Leclercq, Angeles M Esteban, Mathieu Castex, Ebrahim SotoudehAbstract:Abstract The trial investigated the effects of dietary supplementation with the commercial prebiotic galactooligosaccharide (1% GOS; GOS diet), the commercial probiotic Pediococcus acidilactici MA18/5 M (6.3 log CFU g− 1 PA; PA diet) and their combination as synbiotic (1% GOS and 6.3 log CFU g− 1 PA; SYN diet) on the growth, innate immunity and disease resistance of juvenile rockfish (Sebastes schlegeli). Triplicate groups of fish (18.2 ± 0.3 g) were fed one of the four diets for 8 weeks and then subjected to a standard challenge with Edwardsiella tarda by intraperitoneal injection. The results showed significant (P
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probiotic Pediococcus acidilactici modulates both localised intestinal and peripheral immunity in tilapia oreochromis niloticus
Fish & Shellfish Immunology, 2013Co-Authors: Benedict Standen, Mathieu Castex, S J Davies, Andrew D Foey, Giorgia Gioacchini, Oliana Carnevali, Daniel L MerrifieldAbstract:The application of probiotics in aquaculture has received concerted research efforts but the localised intestinal immunological response of fish to probiotic bacteria is poorly understood. Therefore, a study was conducted to evaluate the probiotic effect of Pediococcus acidilactici on Nile tilapia (Oreochromis niloticus) with specific emphasis on intestinal health and probiotic levels as well as system level responses such as growth performance, feed utilization and haemato-immunological parameters under non-challenged conditions. Fish (9.19 ± 0.04 g) were fed either a control diet or a P. acidilactici supplemented diet (at 2.81 × 10(6) CFU g(-)(1)) for six weeks. At the end of the study the probiotic was observed to populate the intestine, accounting for ca. 3% (1.59 × 10(5) CFU g(-)(1)) of the cultivable intestinal bacterial load. Real-time PCR indicated that the probiotic treatment may potentiate the immune-responsiveness of the intestine as up-regulation of the gene expression of the pro-inflammatory cytokine TNFα was observed in the probiotic fed fish (P 0.05).
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probiotic Pediococcus acidilactici modulates both localised intestinal and peripheral immunity in tilapia oreochromis niloticus
Fish & Shellfish Immunology, 2013Co-Authors: Benedict Standen, Mathieu Castex, S J Davies, Andrew D Foey, Giorgia Gioacchini, Oliana Carnevali, Mark D Rawling, Daniel L MerrifieldAbstract:Abstract The application of probiotics in aquaculture has received concerted research efforts but the localised intestinal immunological response of fish to probiotic bacteria is poorly understood. Therefore, a study was conducted to evaluate the probiotic effect of Pediococcus acidilactici on Nile tilapia ( Oreochromis niloticus ) with specific emphasis on intestinal health and probiotic levels as well as system level responses such as growth performance, feed utilization and haemato-immunological parameters under non-challenged conditions. Fish (9.19 ± 0.04 g) were fed either a control diet or a P. acidilactici supplemented diet (at 2.81 × 10 6 CFU g − 1 ) for six weeks. At the end of the study the probiotic was observed to populate the intestine, accounting for ca. 3% (1.59 × 10 5 CFU g − 1 ) of the cultivable intestinal bacterial load. Real-time PCR indicated that the probiotic treatment may potentiate the immune-responsiveness of the intestine as up-regulation of the gene expression of the pro-inflammatory cytokine TNFα was observed in the probiotic fed fish ( P P. acidilactici fed tilapia after six weeks ( P P = 0.08). Concomitantly at week six, along with elevated IELs and elevated TNFα mRNA levels in the intestine, an increased abundance of circulating neutrophils and monocytes were observed in fish fed the probiotic supplemented diet ( P P > 0.05).
Zhongyang Qiu - One of the best experts on this subject based on the ideXlab platform.
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A short-chain dehydrogenase plays a key role in cellulosic D-lactic acid fermentability of Pediococcus acidilactici.
Bioresource technology, 2019Co-Authors: Zhongyang Qiu, Qiuqiang Gao, Chun Fang, Jie BaoAbstract:Abstract Phenolic aldehydes from lignocellulose pretreatment are strong inhibitors of cell growth and metabolism of cellulosic lactic acid bacteria. Their low solubility and recalcitrance highly reduce the removal efficiency of various detoxification methods. This study shows a simultaneous conversion of phenolic aldehydes and fermentation of D-lactic acid by Pediococcus acidilactici using corn stover feedstock. Vanillin was found to be the strongest phenolic aldehyde inhibitor to P. acidilactici. The overexpression of a short-chain dehydrogenase encoded by the gene CGS9114_RS09725 from Corynebacterium glutamicum was identified to play a key role in D-lactic acid fermentability of P. acidilactici. The engineered P. acidilactici with the genome integration of CGS9114_RS09725 showed the accelerated vanillin reduction and improved cellulosic D-lactic acid production. This study reveals that vanillin conversion is crucial for D-lactic acid fermentation, and the direct expression of a specific vanillin reduction gene in lactic acid bacterium efficiently improves cellulosic D-lactic acid production.
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Engineering Pediococcus acidilactici with xylose assimilation pathway for high titer cellulosic L-lactic acid fermentation
Bioresource Technology, 2018Co-Authors: Zhongyang Qiu, Qiuqiang Gao, Jie BaoAbstract:Xylose-assimilating pathways were constructed in the parental Pediococcus acidilactici strain and evolutionarily adapted to yield a highly stable co-fermentation strain for L-lactic acid production. The phosphoketolase pathway (PK) was blocked for reduction of acetic acid generation by disrupting phosphoketolase (pkt) gene. The pentose phosphate pathway (PPP) was reconstructed for xylose assimilation by integrating four heterologous genes encoding transketolase (tkt), transaldolase (tal), xylose isomerase (xylA) and xylulokinase (xylB) into the P. acidilactici chromosome. The xylose-assimilating ability of the constructed strain was significantly improved by long term adaptive evolution. The engineered strain was applied to the simultaneous saccharification and co-fermentation (SSCF) under high solids loading of wheat straw. The L-lactic acid titer, productivity and xylose conversion reached the record high at 130.8 ± 1.6 g/L, 1.82 ± 0.0 g/L/h, and 94.9 ± 0.0%, respectively. This study provided an important strain and process prototype for production of high titer cellulosic L-lactic acid.
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Constructing xylose-assimilating pathways in Pediococcus acidilactici for high titer D-lactic acid fermentation from corn stover feedstock
Bioresource Technology, 2017Co-Authors: Zhongyang Qiu, Qiuqiang Gao, Jie BaoAbstract:Xylose-assimilating pathway was constructed in a D-lactic acid producing Pediococcus acidilactici strain and evolutionary adapted to yield a co-fermentation strain P. acidilactici ZY15 with 97.3 g/L of D-lactic acid and xylose conversion of 92.6% obtained in the high solids content simultaneous saccharification and co-fermentation (SSCF) of dry dilute acid pretreated and biodetoxified corn stover feedstock. The heterologous genes encoding xylose isomerase (xylA) and xylulokinase (xylB) were screened and integrated into the P. acidilactici chromosome. The metabolic flux to acetic acid in phosphoketolase pathway was re-directed to pentose phosphate pathway by substituting the endogenous phosphoketolase gene (pkt) with the heterologous transketolase (tkt) and transaldolase (tal) genes. The xylose-assimilating ability of the newly constructed P. acidilactici strain was significantly improved by adaptive evolution. This study provided an important strain and process prototype for high titer D-lactic acid production from lignocellulose feedstock with efficient xylose assimilation.
S J Davies - One of the best experts on this subject based on the ideXlab platform.
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probiotic Pediococcus acidilactici modulates both localised intestinal and peripheral immunity in tilapia oreochromis niloticus
Fish & Shellfish Immunology, 2013Co-Authors: Benedict Standen, Mathieu Castex, S J Davies, Andrew D Foey, Giorgia Gioacchini, Oliana Carnevali, Daniel L MerrifieldAbstract:The application of probiotics in aquaculture has received concerted research efforts but the localised intestinal immunological response of fish to probiotic bacteria is poorly understood. Therefore, a study was conducted to evaluate the probiotic effect of Pediococcus acidilactici on Nile tilapia (Oreochromis niloticus) with specific emphasis on intestinal health and probiotic levels as well as system level responses such as growth performance, feed utilization and haemato-immunological parameters under non-challenged conditions. Fish (9.19 ± 0.04 g) were fed either a control diet or a P. acidilactici supplemented diet (at 2.81 × 10(6) CFU g(-)(1)) for six weeks. At the end of the study the probiotic was observed to populate the intestine, accounting for ca. 3% (1.59 × 10(5) CFU g(-)(1)) of the cultivable intestinal bacterial load. Real-time PCR indicated that the probiotic treatment may potentiate the immune-responsiveness of the intestine as up-regulation of the gene expression of the pro-inflammatory cytokine TNFα was observed in the probiotic fed fish (P 0.05).
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probiotic Pediococcus acidilactici modulates both localised intestinal and peripheral immunity in tilapia oreochromis niloticus
Fish & Shellfish Immunology, 2013Co-Authors: Benedict Standen, Mathieu Castex, S J Davies, Andrew D Foey, Giorgia Gioacchini, Oliana Carnevali, Mark D Rawling, Daniel L MerrifieldAbstract:Abstract The application of probiotics in aquaculture has received concerted research efforts but the localised intestinal immunological response of fish to probiotic bacteria is poorly understood. Therefore, a study was conducted to evaluate the probiotic effect of Pediococcus acidilactici on Nile tilapia ( Oreochromis niloticus ) with specific emphasis on intestinal health and probiotic levels as well as system level responses such as growth performance, feed utilization and haemato-immunological parameters under non-challenged conditions. Fish (9.19 ± 0.04 g) were fed either a control diet or a P. acidilactici supplemented diet (at 2.81 × 10 6 CFU g − 1 ) for six weeks. At the end of the study the probiotic was observed to populate the intestine, accounting for ca. 3% (1.59 × 10 5 CFU g − 1 ) of the cultivable intestinal bacterial load. Real-time PCR indicated that the probiotic treatment may potentiate the immune-responsiveness of the intestine as up-regulation of the gene expression of the pro-inflammatory cytokine TNFα was observed in the probiotic fed fish ( P P. acidilactici fed tilapia after six weeks ( P P = 0.08). Concomitantly at week six, along with elevated IELs and elevated TNFα mRNA levels in the intestine, an increased abundance of circulating neutrophils and monocytes were observed in fish fed the probiotic supplemented diet ( P P > 0.05).
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the effect of Pediococcus acidilactici on the gut microbiota and immune status of on growing red tilapia oreochromis niloticus
Journal of Applied Microbiology, 2010Co-Authors: Robert M W Ferguson, Daniel L Merrifield, Mark D Rawling, Glenn M Harper, Sanaa A Mustafa, Simona Picchietti, Jose Luis Balcazar, S J DaviesAbstract:Aim: To assess Pediococcus acidilactici as a dietary supplement for on-growing red tilapia (Oreochromis niloticus). Methods and Results: Tilapia were fed either a control diet or control diet supplemented with Ped. acidilactici at 10 7 CFU g -1 for 32 days. Ped. acidilactici colonized the intestinal tract and significantly affected the intestinal microbial communities. PCR-DGGE revealed direct antagonism of gastric Ped. acidilactici with an endogenous uncultured bacterium during a period of reverting to nonsupplemented feeding. Light microscopy revealed that gut integrity and leucocyte levels were unaffec ted by Ped. acidilactici; however, blood leucocyte levels and serum lysozyme activity were elevated after 14-days' feeding. No significant improvements in growth performance were observed at the end of the trial (day 32), but survival was significantly higher in the probiotic group. Conclusions: The study demonstrates that oral supplementation of Ped. acidilactici modulates intestinal bacterial communities in on-growing red tilapia and also stimulates some aspects of the nonspecific immune response. Significance and Impact of the study: To our knowledge this is the first study assessing the effects of probiotics on the gut microbiota of tilapia using culture-independent methods. Such methods are crucial to understand the mechanisms which underpin and mediate host benefits. © 2010 The Society for Applied Microbiology.