Bacillus subtilis AB1 controls Aeromonas infection in rainbow trout (Oncorhynchus mykiss, Walbaum)

Probiotics in fish and shellfish culture: immunomodulatory and ecophysiological responses

Aquaculture is emerging as one of the most viable and promising enterprises for keeping pace with the surging need for animal protein, providing nutritional and food security to humans, particularly those residing in regions where livestock is relatively scarce. With every step toward intensification of aquaculture practices, there is an increase in the stress level in the animal as well as the environment. Hence, disease outbreak is being increasingly recognized as one of the most important constraints to aquaculture production in many countries, including India. Conventionally, the disease control in aquaculture has relied on the use of chemical compounds and antibiotics. The development of non-antibiotic and environmentally friendly agents is one of the key factors for health management in aquaculture. Consequently, with the emerging need for environmentally friendly aquaculture, the use of alternatives to antibiotic growth promoters in fish nutrition is now widely accepted. In recent years, probiotics have taken center stage and are being used as an unconventional approach that has numerous beneficial effects in fish and shellfish culture: improved activity of gastrointestinal microbiota and enhanced immune status, disease resistance, survival, feed utilization and growth performance. As natural products, probiotics have much potential to increase the efficiency and sustainability of aquaculture production. Therefore, comprehensive research to fully characterize the intestinal microbiota of prominent fish species, mechanisms of action of probiotics and their effects on the intestinal ecosystem, immunity, fish health and performance is reasonable. This review highlights the classifications and applications of probiotics in aquaculture. The review also summarizes the advancement and research highlights of the probiotic status and mode of action, which are of great significance from an ecofriendly, sustainable, intensive aquaculture point of view.

Dietary supplementation of Bacillus subtilis and fructooligosaccharide enhance the growth, non-specific immunity of juvenile ovate pompano, Trachinotus ovatus and its disease resistance against Vibrio vulnificus

A feeding trial was conducted to investigate the effects of dietary administration of probiotic Bacillus subtilis and prebiotic fructooligosaccharide (FOS) on growth performance, immune responses and disease resistance of juvenile ovate pompano, Trachinotus ovatus. One thousand six hundred and twenty individuals (initial body weight: 10.32 ± 0.46 g, mean ± S.E) were fed nine practical diets according to a 3 × 3 factorial design: the basal diet as the control diet supplemented with three levels of B. subtilis (0, 1.05 × 10(7) or 5.62 × 10(7) CFU g(-1) diet), crossed with 0, 0.2% or 0.4% FOS. After an 8-week feeding experimental period, six fish per cage were sampled for immunity determination. Then 18 fish of each cage left were challenged by Vibrio vulnificus. The results showed that fish fed with 5.62 × 10(7) CFU B. subtilis g(-1) in combination with 0.2% FOS produced the highest specific growth rate, and were significantly higher than the groups fed with 0 and 0.2% FOS without B. subtilis supplementation (P < 0.05). Feed efficiency ratio significantly increased with the increasing doses of dietary FOS without B. subtilis added (P < 0.05). The immune assay showed that fish fed with the control diet produced the lowest respiratory burst activity and was significantly different from the groups fed the diets containing 0.2% FOS at each B. subtilis level and containing 0.4% FOS single (P < 0.05). Phagocytic activity was significantly decreased with the increasing doses of dietary B. subtilis at 0.4% FOS level (P < 0.05). Alternative complement pathway activity of the fish fed with 0.2% FOS single was significantly lower than those fed with 5.62 × 10(7) CFU B. subtilis g(-1) diet supplemented at each FOS level (P < 0.05). Fish fed with the control diet had the lowest lysozyme activity, and were significantly different from those fed with 0.2 or 0.4% FOS at 1.05 and 5.62 × 10(7) CFU B. subtilis g(-1) diet level. Moreover, fish fed with diets supplemented with 0.2% and 0.4% FOS at each B. subtilis level had notably lower cumulative mortality after 10 days following V. vulnificus infection (P < 0.05). Under the experimental conditions, dietary B. subtilis and FOS had a significant interaction on enhancing the immune responses and disease resistance of juvenile ovate pompano (P < 0.05).

Immunostimulation by poly-β hydroxybutyrate-hydroxyvalerate (PHB-HV) from Bacillus thuringiensis in Oreochromis mossambicus

The present study was designed to test the immunostimulatory efficacy of poly-β hydroxybutyrate-hydroxyvalerate (PHB-HV) extracted from Bacillus thuringiensis B.t.A102 on the immune system of Oreochromis mossambicus. Fish were fed with 0%, 1%, 3% or 5% PHB-HV supplemented feed and were bled at regular intervals of 5 days. The specific immune response was measured in terms of antibody response to sheep red blood cells, the nonspecific immune mechanisms were analysed in terms of serum lysozyme activity, total peroxidases activity and antiprotease activity. The overall functional immunity was tested by experimental challenge with live virulent Aeromonas hydrophila. The results revealed that all the doses of PHB-HV supplementation in feed were effective in stimulating both specific and nonspecific immune mechanisms. The bacterial challenge experiment showed that highest dose of 5% PHB-HV supplementation was more effective than 1% and 3% doses. The study concludes that PHB-HV can be used as a potential immunostimulant in finfish aquaculture.

Effects of three strains of intestinal autochthonous bacteria and their extracellular products on the immune response and disease resistance of common carp, Cyprinus carpio

The study isolated three strains of intestinal autochthonous bacteria Aeromonas veronii BA-1, Vibrio lentus BA-2, and Flavobacterium sasangense BA-3 from the intestinal tract of the common carp (Cyprinus carpio). To reveal the effects of these three strains of bacteria on the innate immunity of carp, the lysozyme, complement C3, total serum protein, albumin and globulin levels, respiratory burst activity, phagocytic activity by blood leucocytes and the expression of IL-1b, lysozyme-C, and TNF-α were examined after feeding with seven different diets for up to 28 days. Also the survival of carp against Aeromonas hydrophila was challenged for 14 days. The carp were fed seven different diets: one control, three diets supplemented with 1 × 10(8) cell g(-1) of carp intestinal bacteria BA-1 (Group D-I), BA-2 (Group D-II) and BA-3 (Group D-III), and three diets supplemented with extracellular products FA-1 (Group E-I), FA-2 (Group E-II) and FA-3 (Group E-III) which were corresponding to the strains BA-1, BA-2, and BA-3, respectively, up to 28 days. For groups D-I, D-III, E-I and E-III, the innate immune parameters of carp were significantly increased, the expression of three immune-related genes in blood was significantly up-regulated examined during 7, 14, and 21 days of feeding, and the survival rate was improved. The study indicates that the two isolated intestinal autochthonous bacteria A. veronii BA-1 and F. sasangense BA-3 could positively influence immune response and enhance disease resistance of carp against A. hydrophila infection.

Dietary synbiotic application modulates Atlantic salmon (Salmo salar) intestinal microbial communities and intestinal immunity

A feeding trial was conducted to determine the effect of dietary administration of Pediococcus acidilactici MA18/5M and short chain fructooligosaccharides (scFOS) on Atlantic salmon (Salmo salar L.) intestinal health. Salmon (initial average weight 250 g) were allocated into triplicate sea pens and were fed either a control diet (commercial diet: 45% protein, 20% lipid) or a synbiotic treatment diet (control diet + P. acidilactici at 3.5 g kg(-1) and 7 g kg(-1) scFOS) for 63 days. At the end of this period, fish were sampled for intestinal microbiology, intestinal histology and the expression of selected immune-related genes (IL1β, TNFα, IL8, TLR3 and MX-1) in the intestine. Compared to the control fish, the total bacterial levels were significantly lower in the anterior mucosa, posterior mucosa and posterior digesta of the synbiotic fed fish. qPCR revealed good recovery (log 6 bacteria g(-1)) of the probiotic in the intestinal digesta of the synbiotic fed fish and PCR-DGGE revealed that the number of OTUs, as well as the microbial community diversity and richness were significantly higher in the anterior digesta of the synbiotic fed fish than the control. Compared to the control fed fish, the mucosal fold (villi) length and the infiltration of epithelial leucocytes were significantly higher in the anterior and posterior intestine, respectively, in the synbiotic group. Real-time PCR demonstrated that all of the genes investigated were significantly up-regulated in the anterior and posterior intestine of the synbiotic fed salmon, compared to the control group. At the systemic level, serum lysozyme activity was significantly higher in the synbiotic fed fish and growth performance, feed utilisation and biometric measurements (condition factor, gutted weight and gut loss) were not affected. Together these results suggest that the synbiotic modulation of the gut microbiota has a protective action on the intestinal mucosal cells, improving morphology and stimulating the innate immune response without negatively affecting growth performance or feed utilization of farmed Atlantic salmon.

Effects of potential probiotic Bacillus amyloliquefaciens [corrected] FPTB16 on systemic and cutaneous mucosal immune responses and disease resistance of catla (Catla catla)

Effects of dietary administration of Bacillus amyloliquefaciens FPTB16 on systemic and mucosal immunity and disease resistance of catla (Catla catla) against Edwardsiella tarda infection were evaluated in the present study. The laboratory maintained B. amyloliquefaciens was used to study antagonistic activity against fish pathogenic bacteria by agar well diffusion assay. Healthy catla were challenged by this bacterium for determination of its safety. For preparation of probiotic supplemented diet, the bacteria were added to the basal diet (control) at three different inclusion levels i.e., 1 × 10(9), 1 × 10(8) and 1 × 10(7) CFU/g diet. Fish (weight 25-30 g) were fed with these diets and various immune parameters and disease resistance study were conducted at 4 weeks and 8 weeks post-feeding. The bacterial antagonism study showed inhibition zone against E. tarda, Aeromonas hydrophila, Vibrio parahaemolyticus and V. harveyi. B. amyloliquefaciens was harmless to catla as neither mortalities nor morbidities were observed after the challenge. Study of different systemic and mucosal immunological parameters viz. superoxide anion production and nitric oxide production, myeloperoxidase content, lysozyme activity and total protein content showed significant enhancement (p < 0.05) in fish fed with 10(8) and 10(9) CFU/g B. amyloliquefaciens at both time points with the highest values observed in case of 10(9) CFU/g. For fish fed with 10(7) CFU/g B. amyloliquefaciens, all the parameters showed significant enhancement (p < 0.05) at both time points except the lysozyme activity of serum at 8 weeks. Diet containing 10(8) and 10(9) CFU/g B. amyloliquefaciens significantly enhanced (p < 0.05) the resistance of catla against bacterial challenge at both time points. These results collectively suggest that B. amyloliquefaciens is a potential probiotic species and can be used in aquaculture to improve health status and disease resistance with an optimal dietary supplementation of 10(9) CFU/g.

Effects of dietary supplementation of probiotic Shewanella colwelliana WA64, Shewanella olleyana WA65 on the innate immunity and disease resistance of abalone, Haliotis discus hannai Ino

The effects of dietary administration of two probiotics, Shewanella colwelliana WA64 and Shewanella olleyana WA65, on the innate immunity of abalone (Haliotis discus hannai Ino), and survival of juvenile abalone challenged with Vibrio harveyi have been studied. Two groups of abalone were fed with three different diets: one control, and two diets supplemented with 10(9) cell g(-1) of probiotic WA64 (WA64 diet) and WA65 (WA65 diet) for up to four weeks. Results showed that abalone fed diets containing S. colwelliana WA64 and S. olleyana WA65 had led to an enhanced cellular and humoral immune response, notably higher haemocytes, respiratory burst activity, serum lysozyme activity and total protein levels were recorded after one week of probiotic administration. On the other hand, mortality after the challenges with V. harveyi in the group fed with control diet ranged from 77 to 80%, while mortality rates observed in the groups fed with diets supplemented with WA64 and WA65 ranged from 27 to 50% and 30-43%, respectively. The results demonstrated potential for S. colwelliana WA64 and S. olleyana WA65 to improve innate immunity and disease resistance in H. discus hannai.

Changes in intestinal morphology and microbiota caused by dietary administration of inulin and Bacillus subtilis in gilthead sea bream (Sparus aurata L.) specimens

Changes produced in gilthead sea bream (Sparus aurata L.) intestinal morphology and microbiota caused by dietary administration of inulin and Bacillus subtilis have been studied. Gilthead sea bream specimens were fed diets containing 0 (control), inulin (10 g kg(-1)), B. subtilis (10(7) cfu g(-1)), or B. subtilis + inulin (10(7) cfu g(-1) + 10 g kg(-1)) for four weeks. Curiously, fish fed the experimental diets (inulin, B. subtilis, or B. subtilis + inulin) showed the same morphological alterations when studied by light and electron microscopy, while significant differences in the signs of intestinal damage were detected by the morphometric study. All of the observed alterations were present only in the gut mucosa, and intestinal morphometric study revealed no effect of inulin or B. subtilis on the intestinal absorptive area. Furthermore, experimental diets cause important alterations in the intestinal microbiota by significantly decreasing bacterial diversity, as demonstrated by the specific richness, Shannon, and range-weighted richness indices. The observed alterations demonstrate that fish fed experimental diets had different signs of gut oedema and inflammation that could compromise their body homeostasis, which is mainly maintained by the epithelial lining of the gastrointestinal tract. To our knowledge, this is the first in vivo study regarding the implications of the use of synbiotics (conjunction of probiotics and prebiotics) on fish gut morphology and microbiota.

Probiotic therapy reduces periodontal tissue destruction and improves the intestinal morphology in rats with ligature-induced periodontitis

BACKGROUND

With increase in the incidence of resistance to antibiotics, probiotics are emerging as a promising adjunctive periodontal therapy. The authors of this study evaluate the influence of probiotic (PROB) supplementation on ligature-induced periodontitis (LIP) and intestinal morphology in rats.

METHODS

Thirty-two rats were randomly divided into four groups: control (C), LIP, PROB, and LIP/PROB. In groups PROB and LIP/PROB, the PROB was administered orally by addition to the drinking water of the animals for 44 days. In groups LIP and LIP/PROB, the mandibular right first molar of the animals received a cotton ligature that was left in the same position for 14 days. All animals were euthanized 44 days after the start of the PROB supplementation. The jaws were resected and histomorphometric analyses were performed. The measurements included evaluation of attachment loss (AL) and alveolar bone level (ABL) on the distal root of the mandibular first molar. Samples of the duodenum, jejunum, and ileum were also dissected from each animal to evaluate the villous height (VH) and crypt depth (CD). The data obtained were subjected to statistical analyses (analysis of variance, Tukey; P <0.05).

RESULTS

Mean values of AL and ABL were significantly higher in group LIP compared with group LIP/PROB (AL: 3.05 ± 0.57 mm and 1.78 ± 0.63 mm, respectively; ABL: 4.21 ± 0.42 mm and 3.38 ± 0.17 mm, respectively). In group LIP/PROB, the mean values of VH and CD of the jejunum were significantly higher than the ones from group LIP (VH: 672.1 ± 83.3 µm and 528.0 ± 51.7 µm, respectively; CD: 463.8 ± 100.9 µm and 269.0 ± 48.4 µm, respectively).

CONCLUSIONS

It can be concluded that PROB supplementation 1) reduces AL and alveolar bone loss in rats with LIP and 2) can protect the small intestine from reactive changes induced by LIP.

Histological alterations and microbial ecology of the intestine in gilthead seabream (Sparus aurata L.) fed dietary probiotics and microalgae

The effects on histology and microbial ecology in gilthead seabream (Sparus aurata) intestine caused by dietary probiotic and microalgae were studied. Fish were fed non-supplemented (C, control) or supplemented diets with Tetraselmis chuii, Phaeodactylum tricornutum and Bacillus subtilis single or combined (diets T, P, B, BT and BP) for 4 weeks. Curiously, fish fed the experimental diets showed similar morphological alterations when studied by light and electron microscopy and significant signs of intestinal damage were detected. No effect of microalgae or B. subtilis on the intestinal absorptive area was observed, whereas the number of goblet cells and IELs were significantly lower in fish fed the T, P, B and BT diets and T, BT and BP diets, respectively. Interestingly, only the diets containing B. subtilis resulted in a significant reduction of microvilli height. Alterations such as wide intercellular spaces and large vacuoles in enterocytes were observed in fish fed T, B, BT, BT and P in lesser degrees. These observations demonstrate that fish fed experimental diets presented different signs of oedema and inflammation that could compromise their body homeostasis. Moreover, the experimental diets cause important alterations in the intestinal microbiota by a significant decrease in bacterial diversity, as demonstrated by the fall in specific richness, Shannon and range-weighted richness indices. To our knowledge, this is the first in vivo study regarding the implications of the use of probiotics in combination with immunostimulants on fish intestinal morphology and microbiota. More morphofunctional studies are needed in order to correlate the nutritional and immune aspects of fish gut.

Effects of marine silages enriched with Lactobacillus sakei 5-4 on haemato-immunological and growth response in Pacific red snapper (Lutjanus peru) exposed to Aeromonas veronii

Combined effects of marine silages enriched with Lactobacillus sakei 5-4 were evaluated on growth performance, immune activity and disease resistance of Pacific red snapper (Lutjanus peru) against Aeromonas veronii infection. The experimental fish were divided into three groups which were fed with each one of the following diets: silage-probiotic-free diet (control, C group), Pacific creole-fish silage diet supplemented with live L. sakei (10(6) CFU g(-1)) (FSLact group) and Humboldt squid silage diet supplemented with live L. sakei (10(6) CFU g(-1)) (SSLact group) for 6 weeks. After 6 weeks, fish were immunocompromised with pathogenic A. veronii and spleen and liver samples were processed for histopathological studies. Generally, the results showed enhanced growth performance in fish fed the diet containing SSLact at 6 and 7 weeks compared with fish fed control diet. Addition of SSLact had an increase in plasmatic protein at week 6 and post-challenge. Hemoglobin concentration increased after challenge in fish fed with SSLact compared to control group. At week 6 and post-challenge the results indicated that, the fish groups which received diet supplemented with SSLact revealed significant increase in humoral immune parameters. Histologically, fish fed C diets showed marked fatty degeneration and great activation of melanomacrophage centers compare with SSLact and FSLact groups. These results support the idea that the marine silages with squid as protein source enriched or combined with L. sakei 5-4 increases the body weight and stimulates the physiological and humoral immune parameters in Pacific red snapper infected with A. veronii.

Identification of Bacillus strains for biological control of catfish pathogens

Bacillus strains isolated from soil or channel catfish intestine were screened for their antagonism against Edwardsiella ictaluri and Aeromonas hydrophila, the causative agents of enteric septicemia of catfish (ESC) and motile aeromonad septicaemia (MAS), respectively. Twenty one strains were selected and their antagonistic activity against other aquatic pathogens was also tested. Each of the top 21 strains expressed antagonistic activity against multiple aquatic bacterial pathogens including Edwardsiella tarda, Streptococcus iniae, Yersinia ruckeri, Flavobacterium columnare, and/or the oomycete Saprolegnia ferax. Survival of the 21 Bacillus strains in the intestine of catfish was determined as Bacillus CFU/g of intestinal tissue of catfish after feeding Bacillus spore-supplemented feed for seven days followed by normal feed for three days. Five Bacillus strains that showed good antimicrobial activity and intestinal survival were incorporated into feed in spore form at a dose of 8×10(7) CFU/g and fed to channel catfish for 14 days before they were challenged by E. ictaluri in replicate. Two Bacillus subtilis strains conferred significant benefit in reducing catfish mortality (P<0.05). A similar challenge experiment conducted in Vietnam with four of the five Bacillus strains also showed protective effects against E. ictaluri in striped catfish. Safety of the four strains exhibiting the strongest biological control in vivo was also investigated in terms of whether the strains contain plasmids or express resistance to clinically important antibiotics. The Bacillus strains identified from this study have good potential to mediate disease control as probiotic feed additives for catfish aquaculture.

Effects of dietary Bacillus subtilis, Tetraselmis chuii, and Phaeodactylum tricornutum, singularly or in combination, on the immune response and disease resistance of sea bream (Sparus aurata L.)

Combined or individual effects of two microalgae (Phaeodactylum tricornutum and Tetraselmis chuii) and Bacillus subtilis on immune response, gene expression, and survival to challenge with Photobacterium damselae subsp. piscicida of gilthead sea bream were investigated. To test the capacity of B. subtilis to grow employing the microalgae polysaccharides as energy and carbon source, an in vitro assay was defined, and demonstrated that the digestion product of microalgae, mainly P. tricornutum, supported the growth of B. subtilis much better than glucose. For the in vivo study, fish were distributed in six equal groups (each of two replicates) and received one of the following experimental diets: C) control, non-supplemented diet; T) T. chuii 100 g kg(-1); P) P. tricornutum 100 g kg(-1); B) B. subtilis (10(7) cfu g(-1)); BT) B. subtilis (10(7) cfu g(-1))+T. chuii (100 g kg(-1)); and BP) B. subtilis (10(7) cfu g(-1))+P. tricornutum (100 g kg(-1)). The complement activity, serum IgM level, respiratory burst, phagocytic activity, and expression of seven selected immune-related genes in head-kidney were evaluated following two and four weeks of treatment. At the end of the feeding trial, fish were challenged by intraperitoneal injection of LD(50) concentration of P. damselae subsp. piscicida and mortality was recorded. This is the first study testing the immunomodulatory capacity of the microalgae used in the present work. The dietary applications of B. subtilis, T. chuii, and P. tricornutum, singly or in combination, may exhibit up-regulating effects on gilthead sea bream immune parameters. P. tricornutum demonstrated the highest immunostimulant activity. There were no significant differences between combination feeding and feeding ingredients separately. Our results demonstrated the potential of microalgae as immunostimulants for fish, although further studies regarding the implications and effects of a stimulated immune system against pathogens, especially the protective capacity against specific diseases, are necessary.

Increases in immune parameters by inulin and Bacillus subtilis dietary administration to gilthead seabream (Sparus aurata L.) did not correlate with disease resistance to Photobacterium damselae

The present work evaluates the effects of inulin and Bacillus subtilis, single or combined, on immune parameters, immune-related gene expression and protection against Photobacterium damselae subsp. piscicida in gilthead seabream (Sparus aurata). Three trials were conducted. In the first trial, different concentrations of inulin (10, 15 and 30 g kg(-1)) (as a prebiotic) were administered to determine the optimal concentration for stimulating the seabream's immune system. In the second trial, the optimum concentration of inulin (10 g kg(-1)) was combined with B. subtilis (as a probiotic). Following two and four weeks of the treatment, the main immune parameters, as well as the expression of seven immune-related genes, were measured. In the final trial, fish fed the same diet as in the second trial were challenged intraperitoneally with P. damselae subsp. piscicida (10(9) cfu g(-1)). Treatment groups for the second and third trial were control (non-supplemented diet), inulin (10 g kg(-1)), B. subtilis (10(7) cfu g(-1)) and inulin + B. subtilis (10 g kg(-1) and 10(7) cfu g(-1) respectively). Dietary administration of inulin or B. subtilis for two weeks stimulated the serum complement activity and the IgM level, as well as leucocyte phagocytic activity; furthermore, inulin stimulated leucocyte respiratory burst activity. When inulin and B. subtilis were administered together (as a synbiotic), only the serum complement activity and the IgM level increased in a statistically significant manner. Furthermore, the complement activity showed a significant increase in fish fed the three experimental diets for four weeks. The challenge experiment showed that the fish fed inulin or the synbiotic diet had non-significantly lower or significantly higher cumulative mortality, respectively, compared with the control group (non-supplemented diet). These results suggest that inulin and B. subtilis modulate the immune response of the gilthead seabream, although the combined administration increases susceptibility to infection by P. damselae subsp. piscicida.

Pseudomonas M162 confers protection against rainbow trout fry syndrome by stimulating immunity

AIMS

  To evaluate the antagonistic effect of Pseudomonas M162 against Flavobacterium psychrophilum.

METHODS AND RESULTS

  The antagonistic activity of M162 was tested in vivo and in vitro, and its mode of action examined by siderophore production and immunological responses of rainbow trout (Oncorhynchus mykiss) fry. Pseudomonas M162 inhibited the growth of Fl. psychrophilum in vitro and increased the resistance of the fish against the pathogen, resulting in a relative per cent survival (RPS) of 39·2%. However, the siderophores produced by M162 did not have an inhibitory effect on Fl. psychrophilum. In fish fed with M162, the probiotic colonized the gastrointestinal tract and stimulated peripheral blood leucocyte counts, serum lysozyme activity and total serum immunoglobulin levels after 3 weeks from the start of feeding.

CONCLUSIONS

  This study showed the potential of Pseudomonas M162 as a probiotic by reducing the mortalities that occurred during an experimental Fl. psychrophilum infection, resulting mainly through the immunostimulatory effects of the bacterium.

SIGNIFICANCE AND IMPACT OF THE STUDY

  Rainbow trout fry syndrome (RTFS) causes high mortalities during the early life stages of the fish's life cycle, partly because their adaptive immunity has not yet fully developed. Thus, immunomodulation by probiotics could be an effective prophylactic method against RTFS.

Aquaculture and stress management: a review of probiotic intervention

To meet the ever-increasing demand for animal protein, aquaculture continuously requires new techniques to increase the production yield. However, with every step towards intensification of aquaculture practices, there is an increase in stress level on the animal as well as on the environment. Feeding practices in aqua farming usually plays an important role, and the addition of various additives to a balanced feed formula to achieve better growth is a common practice among the fish and shrimp culturists. Probiotics, also known as 'bio-friendly agents', such as LAB (Lactobacillus), yeasts and Bacillus sp., can be introduced into the culture environment to control and compete with pathogenic bacteria as well as to promote the growth of the cultured organisms. In addition, probiotics are non-pathogenic and non-toxic micro-organisms, having no undesirable side effects when administered to aquatic organisms. Probiotics are also known to play an important role in developing innate immunity among the fishes, and hence help them to fight against any pathogenic bacterias as well as against environmental stressors. The present review is a brief but informative compilation of the different essential and desirable traits of probiotics, their mode of action and their useful effects on fishes. The review also highlights the role of probiotics in helping the fishes to combat against the different physical, chemical and biological stress.

Effect of Coriolus versicolor supplemented diet on innate immune response and disease resistance in kelp grouper Epinephelus bruneus against Listonella anguillarum

The effect of Coriolus versicolor extract supplemented diets on innate immune response and disease resistance in kelp grouper, Epinephelus bruneus against Listonella anguillarum, is reported. Kelp grouper were divided into four groups of 25 each and fed with C. versicolor enriched diets at 0% (control), 0.01%, 0.1%, and 1.0% level. After 30 days of feeding, all fish were injected interaperitoneally (i.p.) with 50 μl of L. anguillarum (4.7 × 10(7) CFU) to investigate the immune parameters at weeks 1, 2, and 4. The reactive oxygen species and reactive nitrogen species production were significantly enhanced in fish fed with 0.1% and 1.0% supplementation diets from weeks 1-4 when compared to the non enriched diet fed and infected control. The phagocytic activity significantly increased with 0.1% and 1.0% diets on weeks 2 and 4. The leucocyte myeloperoxidase content, lysozyme activity, and total protein level significantly increased when fed with 0.1% and 1.0% supplementation diets from weeks 1-4. The cumulative mortality was 35% and 45% in 1.0% and 0.1% enriched diet fed groups whereas it was 55% and 80% in 0.01% and 0% groups respectively. The present results suggest that diets enriched with C. versicolor at 0.1% or 1.0% level positively enhance the innate immune system and affords protection from L. anguillarum.

Effects of a probiotic, protexin, on the growth performance and hematological parameters in the Oscar (Astronotus ocellatus) fingerlings

This study examined the effects of a probiotic, protexin, on the growth performance and hematological parameters in an ornamental fish, the Oscar Astronotus ocellatus fingerlings. A completely randomized experimental design was applied with three experimental diets each with three replicates. A commercial food, BioMar, was supplemented with protexin at levels of 0.15, 0.5, and 1.0 g kg(-1) dry food and fed three times a day for 60 days. The control diet was prepared with no protexin supplementation. The experimental fish were biometried every 15 days to compare their growth rates at each treatment. For hematological assays, blood samples were prepared every 30 days to measure such parameters as red and white blood cells, hemoglobin, hematocrit, and percentages of lymphocytes, monocytes, neutrophiles, basophiles, and eosinophiles. Based on the results, the fingerlings fed a 0.15 g kg(-1) supplemented food were significantly different from the fish in the other treatments and in the control, with the highest mean of both final weight (35.07 ± 1.19) and body weight gain (30.17 ± 1.08). Significant differences in both hemoglobin concentration and mean red and white blood cells were found between the experimental groups and the control within 2 months. The highest hemoglobin concentration and also red and white blood cells was observed in the fish-fed 0.15 dietary protexin in both months. The results of this study show that the probiotic, protexin, at a level of 0.15 g kg(-1) dry food could have measurable effects on the growth and hematological parameters in the Oscar A. ocellatus fingerlings.

Effects of dietary chitosan and Bacillus subtilis on the growth performance, non-specific immunity and disease resistance of cobia, Rachycentron canadum

The present study was performed to investigate the effects of various levels of dietary Bacillus subtilis and chitosan on the growth performance, non-specific immunity and protection against Vibrio harveyi infection in cobia, Rachycentron canadum. Fish were fed with the control diet and six different experimental diets containing three graded levels of B. subtilis at 2 × 10(10) CFU g(-1) (0.0, 1.0, 2.0 g kg(-1) diet) for each of two levels of chitosan (3.0 and 6.0 g kg(-1) diet). The results of 8 weeks feeding trial showed that the survival rate ranged from 81.3% to 84.0% with no significant difference (P > 0.05). The SGR (%) in the fish fed with dietary treatments was significantly higher than that of the control fish except diet 6 group with 2.0 g kg(-1)B. subtilis and 3.0 g kg(-1) chitosan. The serum lysozyme activities were significantly higher in 6.0 g kg(-1) chitosan groups and no significant differences were observed among B. subtilis levels. The serum ACP activities were significantly higher in 3.0 g kg(-1) chitosan groups at 0.0 and 1.0 g kg(-1)B. subtilis levels; at low chitosan level, the cobia fed diets with 1.0 g kg(-1)B. subtilis had significantly higher serum ACP activity, but at high chitosan level, the cobia fed diets with 2.0 g kg(-1)B. subtilis had significantly higher serum ACP activity. The phagocytosis and respiratory burst activity in the fish fed with dietary treatments was significantly higher than that of the control fish except diet 3 group with 6.0 g kg(-1) chitosan. Moreover, fish fed the diet containing 2.0 g kg(-1)B. subtilis and 6.0 g kg(-1) chitosan had significantly higher post-challenge survival on the 7th day following V. harveyi infection and post-challenge survival showed clearly the synergistic effect of chitosan and B. subtilis. Based on these results, the combination of 1.0 g kg(-1)B. subtilis and 6.0 g kg(-1) chitosan is optimal for the growth, innate immunity and disease resistance of cobia with an 8-week oral administration.

Immunomodulatory effects of secondary metabolites from thermophilic Anoxybacillus kamchatkensis XA-1 on carp, Cyprinus carpio

A bacterial strain with putative immunomodulatory properties was isolated from Xi'an hot springs in China. Comparison of 16S rRNA gene revealed a 97% similarity between the tested strain (designated XA-1) and Anoxybacillus kamchatkensis. Two compounds isolated from the secondary metabolites of XA-1 were identified by spectral data (infrared, nuclear magnetic resonance and mass spectrometry) as: (1) cyclo (Gly-L-Pro) and (2) cyclo (L-Ala-4-hydroxyl-L-Pro). Two cyclic dipeptides showed stimulatory properties towards a range of parameters when a dose of 20mg kg(-1) body weight was intraperitoneally injected in naive common carp, Cyprinus carpio. Innate immune parameters (serum SOD, lysozyme and bactericidal activity, and phagocytic activity by peripheral blood leucocytes) along with the expression of two immune-related genes (IL-1β and iNOS) in blood were examined after 7, 14, 21, and 28 days of injection. In the absence of infection, immunomodulators should ideally not affect normal physiology and immunity of the host; possible negative outcomes of activated immune responses in the naive state are discussed. Protection by two bacterial dipeptides was assessed in an intraperitoneal injection challenge trial with live Aeromonas hydrophila. Both compounds reduced mortality, with the highest survival rate observed in the group that received compound 2 (80%) followed by the group that received compound 1 (65%) while control group scored the worse (15%). Elucidation of the involved protective mechanisms in carp requires future studies.

Effects of dietary supplementation of synbiotic on growth performance, serum biochemical parameters and carcass composition in rainbow trout (Oncorhynchus mykiss) fingerlings

The aim of this study was to evaluate the influence of a synbiotic (Biomin IMBO) on serum parameters and feeding efficiency in rainbow trout (Oncorhynchus mykiss) fingerlings. The fish with initial average weight of 4.59 ± 0.2 g were randomly assigned to four dietary treatments for two months. The dietary treatment (0.5, 1 and 1.5 g/kg of diet) was supplemented with basal diet and non-supplemented basal diet was used as control. After two months, all treatments supplemented with synbiotic showed significant (p < 0.05) increase in final mean weight, weight gain percentage, specific growth rate, condition factor, food conversion efficiency and survival rate, compared to the control group. Among all supplemented treatments, the best result in terms of growth factors and survival was observed in the treatment supplemented with 1 g synbiotic per kilogram of diet. Furthermore, supplementation with symbiotic, specifically 1 and 1.5 g/kg, significantly (p < 0.05) increased the total serum protein, but there was no significant (p > 0.05) difference in globulin content, albumin/globulin ratio, and triglyceride content among experimental treatments. In terms of body composition, carcass protein content of fish fed with synbiotic significantly (p < 0.05) increased compared to the control. These results revealed that a feeding regime with synbiotic for two months led to a significant increase in growth performance, survival rate and feeding efficiency in rainbow trout fingerlings.

Effect of dietary alginic acid on juvenile tilapia (Oreochromis niloticus) intestinal microbial balance, intestinal histology and growth performance

The aim of the present study was to assess the effect of a commercial alginic acid source (Ergosan) on tilapia Oreochromis niloticus intestinal microbial balance, intestinal morphology, and growth parameters. Fish were fed a basal control diet or the basal diet plus a source of alginic acid (5 g kg(-1) Ergosan; Schering-Plough Aquaculture, UK) for 9 weeks. At the end of the trial, light and electron microscopy demonstrated that the morphology of the intestinal tract at the gross and ultra-structural level was not affected by dietary alginic acid inclusion. Both groups of fish displayed healthy, normal morphology with no signs of disease, cell or tissue damage. Intestinal epithelial leucocyte infiltration was not affected by dietary alginic acid. Molecular bacterial profiles derived from PCR-DGGE illustrated highly similar microbial communities (both within the lumen and associated with the intestinal mucosa) in the respective treatment groups. Microbial ecological parameters (e.g. species diversity and richness) also remained unaffected. Although not significant, trends towards elevated survival and body protein content were observed in the alginic acid-fed fish. These results are suggestive that alginic acid does not adversely impact the indigenous gastrointestinal microbial balance and subsequently does not impact upon the epithelial brush border integrity. Validation of non-detrimental impacts of immunostimulatory products on gastric microbiota and epithelial integrity should be pursued in future studies as maintaining microbial balance and epithelial integrity is essential for proper gut functionality.

Immunostimulatory activities of specific bacterial secondary metabolite of Anoxybacillus flavithermus strain SX-4 on carp, Cyprinus carpio

AIMS

  To determine the capacity of secondary metabolite of strain SX-4, to enhance the nonspecific immunity and survival of carp (Cyprinus carpio), and to identify the constituents that are responsible.

METHODS AND RESULTS

  A thermophilic strain SX-4 that is able to produce immunostimulatory metabolite was isolated from sludge sample of hot spring and identified by comparison with 16S rRNA sequences (99% of homology) as Anoxybacillus flavithermus. Bioactivity-guided fractionation of methanol extract from its cell-free culture, one bacterial peptide with the capacity of improving the nonspecific immune responses and disease resistance (relative per cent survival = 66·67%) was obtained and the compound was characterized as cyclo-(L-Pro-Gly) by IR, ESI-MS, (1) H NMR and (13) C NMR spectroscopic analyses. After intraperitoneal administration of this peptide, selected innate immune parameters including phagocytic activity, superoxide anion production, serum lysozyme activity and serum SOD activity, along with immune-related genes expression (i.e. interleukin-1β and inducible nitric oxide synthase), in the blood were found to be significantly increased.

CONCLUSIONS

  The bacterial peptide cyclo-(L-Pro-Gly) significantly enhances nonspecific immunity and survival of carp.

SIGNIFICANCE AND IMPACT OF THE STUDY

  There is a possibility of using cyclo-(L-Pro-Gly) as a better natural immunostimulant, which could have a promising role in aquaculture to prevent diseases and disease outbreaks.

Host-microbiota interactions within the fish intestinal ecosystem

Teleost fish are in direct contact with the aquatic environment, and are therefore in continual contact with a complex and dynamic microbiota, some of which may have implications for health. Mucosal surfaces represent the main sites in which environmental antigens and intestinal microbiota interact with the host. Thus, the gut-associated lymphoid tissues (GALT) must develop mechanisms to discriminate between pathogenic and commensal microorganisms. Colonization of intestinal mucosal surfaces with a normal microbiota has a positive effect on immune regulatory functions of the gut, and disturbance in these immune regulatory functions by an imbalanced microbiota may contribute to the development of diseases. Significant attention has therefore been recently focused on the role of probiotics in the induction or restoration of a disturbed microbiota to its normal beneficial composition. Given this, this article explores the fascinating relationship between the fish immune system and the bacteria that are present in its intestinal microbiota, focusing on the bacterial effect on the development of certain immune responses.

Probiotics and immunity: a fish perspective

Probiotics are usually live microorganisms which when administered in adequate amounts confer a health benefits on host. Nowadays, probiotics are also becoming an integral part of the aquaculture practices to obtain high production. The common probiotics that are used for aquaculture practices include Lactobacillus, Lactococcus, Leuconostoc, Enterococcus, Carnobacterium, Shewanella, Bacillus, Aeromonas, Vibrio, Enterobacter, Pseudomonas, Clostridium, and Saccharomyces species. The involvement of probiotics in nutrition, disease resistance and other beneficial activities in fish has proven beyond any doubt. Among the numerous health benefits attributed to probiotics, modulation of immune system is one of the most commonly purported benefits of the probiotics and their potency to stimulate the systemic and local immunity under in vitro and in vivo conditions is noteworthy. Different probiotics either monospecies or multispecies supplementation can eventually elevate phagocytic, lysozyme, complement, respiratory burst activity as well as expression of various cytokines in fish. Similarly, probiotics can stimulate the gut immune system of fish with marked increase in the number of Ig(+) cells and acidophilic granulocytes. Furthermore, mono-bacterial association studies (with non-probiotic bacterial strains) in gnotobiotic fish also indicate the up-regulation of various immune related genes. Though the exact mode of action of probiotics is yet to be established in any animal including fish, probiotics often exert host specific and strain specific differences in their activities. Various factors like source, type, dose and duration of supplementation of probiotics can significantly affect the immunomodulatory activity of probiotics. The review is therefore, aiming to highlight the immunomodulatory activity of probiotics and also to evaluate the factors that regulate for the optimum induction of immune responses in fish.

Competitive exclusion as a mode of action of a novel Bacillus cereus aquaculture biological agent

AIMS

To determine the contribution of potential modes of action of a Bacillus cereus aquaculture biological control agent in inhibition of the fish pathogen, Aeromonas hydrophila.

METHODS AND RESULTS

When B. cereus was tested in plate well inhibition studies, no production of antimicrobial compounds was detected. Bacillus cereus had a high growth rate (0.96 h(-1)), whereas Aer. hydrophila concentration decreased by c. 70% in co-culture experiments. In nutrient limitation studies, B. cereus had a significantly higher growth rate when cultured under glucose (P < 0.05) and iron (P < 0.01) limitation in comparison with Aer. hydrophila. Bacillus cereus glucose (0.30 g l(-1) h(-1)) and iron (0.60 mg l(-1) h(-1)) uptake rates were also significantly higher (P < 0.01) than the Aer. hydrophila glucose (0.14 g l(-1) h(-1)) and iron (0.43 mg l(-1) h(-1)) uptake rates. Iron uptake was facilitated by siderophore production shown in time profile studies where relative siderophore production was c. 60% through the late exponential and sporulation phases.

CONCLUSIONS

Competitive exclusion by higher growth rate, competition for organic carbon and iron, facilitated by siderophore production, could be identified as mechanisms of pathogen growth inhibition by B. cereus.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study is the first elucidation of the mechanism of action of our novel B. cereus biological agent in growth attenuation of pathogenic Aer. hydrophila. This study enhances the application knowledge and attractiveness for adoption of B. cereus NRRL 100132 for exploitation in aquaculture.

Kocuria SM1 controls vibriosis in rainbow trout (Oncorhynchus mykiss, Walbaum)

AIMS

To develop probiotics for the control of vibriosis caused by Vibrio anguillarum and Vibrio ordalii in finfish.

METHODS AND RESULTS

Kocuria SM1, isolated from the digestive tract of rainbow trout, was administered orally to rainbow trout (Oncorhynchus mykiss) for 2 weeks at a dose equivalent to c. 10(8) cells per g of feed and then challenged intraperitoneally with V. anguillarum and V. ordalii. Use of SM1 led to a reduction in mortalities to 15-20% compared to 74-80% mortalities in the controls. SM1 stimulated both cellular and humoral immune responses in rainbow trout, by elevation of leucocytes (5.5 +/- 0.8 x 10(6) ml(-1) from 3.7 +/- 0.8 x 10(6) ml(-1)), erythrocytes (1.2 +/- 0.1 x 10(8) ml(-1) from 0.8 +/- 0.1 x 10(8) ml(-1)), protein (23 +/- 4.4 mg ml(-1) from 16 +/- 1.3 mg ml(-1)), globulin (15.7 +/- 0.2 mg ml(-1) from 9.9 +/- 0.1 mg ml(-1)) and albumin (7.3 +/- 0.2 mg ml(-1) from 6.1 +/- 0.1 mg ml(-1)) levels, upregulation of respiratory burst (0.05 +/- 0.01 from 0.02 +/- 0.01), complement (56 +/- 7.2 units ml(-1) from 40 +/- 8.0 units ml(-1)), lysozyme (920 +/- 128.8 units ml(-1) from 760 +/- 115.3 units ml(-1)) and bacterial killing activities.

CONCLUSIONS

Kocuria SM1 successfully controlled vibriosis in rainbow trout, and the mode of action reflected stimulation of the host innate immune system.

SIGNIFICANCE AND IMPACT OF THE STUDY

Probiotics can contribute a significant role in fish disease control strategies, and their use may replace some of the inhibitory chemicals currently used in fish farms.

Soybean meal alters autochthonous microbial populations, microvilli morphology and compromises intestinal enterocyte integrity of rainbow trout, Oncorhynchus mykiss (Walbaum)

Abstract Rainbow trout were fed either a diet containing fishmeal (FM) as the crude protein source or a diet containing 50% replacement with soybean meal (SBM) for 16 weeks. An enteritis-like effect was observed in the SBM group; villi, enterocytes and microvilli were noticeably damaged compared with the FM group. The posterior intestine microvilli of SBM-fed fish were significantly shorter and the anterior intestine microvilli significantly less dense than the FM-fed fish. Electron microscopy confirmed the presence of autochthonous bacterial populations associated with microvilli of both fish groups. Reduced density of microvilli consequently led to increased exposure of enterocyte tight junctions, which combined with necrotic enterocytes is likely to diminish the protective barrier of the intestinal epithelium. No significant differences in total viable counts of culturable microbial populations were found between the groups in any of the intestinal regions. A total of 1500 isolates were tentatively placed into groups or genera, according to standard methods. Subsequent partial 16S rRNA sequencing revealed species that have not been identified from the rainbow trout intestine previously. Compared with the FM group levels of Psychrobacter spp. and yeast were considerably higher in the SBM group; a reduction of Aeromonas spp. was also observed.

Influence of probiotic feeding duration on disease resistance and immune parameters in rainbow trout

The effect of feeding the probiotic Kocuria SM1 to rainbow trout (Oncorhynchus mykiss, Walbaum) on disease resistance was evaluated. Thus, rainbow trout were fed Kocuria SM1 supplemented diets at concentrations of approximately 10(8) cells g(-1) feed for up to four weeks, and then challenged intraperitoneally with Vibrio anguillarum at weekly intervals. A two-week feeding regime led to the maximum reduction in mortalities, i.e. 16%, compared to mortalities of 62, 30 and 22% for one, three and four week feeding regimes, respectively. These compared to 70-90% mortalities of the controls. An enhanced cellular and humoral immune response, notably greater head kidney macrophage phagocytic and peroxidase activities, and higher serum lysozyme and total protein levels were recorded after two weeks of probiotic administration. These results reveal that a two-week feeding regime with Kocuria SM1 leads to higher disease protection in rainbow trout, with protection linked to stimulation of immune parameters.

Pseudomonas chlororaphis strain JF3835 reduces mortality of juvenile perch, Perca fluviatilis L., caused by Aeromonas sobria

Motile aeromonad septicaemia caused by Aeromonas sobria is a cause of disease in farmed perch, Perca fluviatilis L., in Switzerland. We have evaluated the potential of a Pseudomonas chlororaphis isolate, obtained from perch intestine, to control A. sobria infection. Inoculation of juvenile perch with P. chlororaphis strain JF3835 prior to infection with A. sobria caused a reduction in A. sobria associated mortalities. Infection of perch with xylE-labelled P. chlororaphis indicated the bacterium is able to transiently colonize juvenile fish and fingerlings.

Ecology and genomics of Bacillus subtilis

Bacillus subtilis is a remarkably diverse bacterial species that is capable of growth within many environments. Recent microarray-based comparative genomic analyses have revealed that members of this species also exhibit considerable genomic diversity. The identification of strain-specific genes might explain how B. subtilis has become so broadly adapted. The goal of identifying ecologically adaptive genes could soon be realized with the imminent release of several new B. subtilis genome sequences. As we embark upon this exciting new era of B. subtilis comparative genomics we review what is currently known about the ecology and evolution of this species.

Enhanced innate immune parameters in Labeo rohita (Ham.) following oral administration of Bacillus subtilis

The present study assessed the use of Bacillus subtilis in fish as a probiotic. The bacterium was administered orally at three different doses 0.5 x 10(7) (T(2)), 1 x 10(7) (T(3)), 1.5 x 10(7) (T(4)) cfu/g feed to Labeo rohita for two weeks. The positive control group (T(1)) and negative control group (T(5,)) were fed feed without B. subtilis for the same period. On the 15th day blood and serum were sampled to determine respiratory burst activity (NBT assay), differential leukocyte counts (DLC) and serum bactericidal activity. Fishes were challenged intraperitoneally with Aeromonas hydrophila O:18 after two weeks in the treatment groups (T(2), T(3) and T(4)) and also in the positive control group(T(1)), while the negative control group (T(5)) was challenged with phosphate buffered saline (PBS, pH 7.2) only. The respiratory burst activity and DLC were assessed on the 3rd day post-challenge. B. subtilis treated fish showed significantly higher (P<0.05) respiratory burst activity and bactericidal activity during the pre-challenge compared with the control groups. The highest respiratory burst activity (0.37+/-0.03) and serum bactericidal activity were recorded in the group (T(4)) fed feed containing B. subtilis at 1.5 x 10(7)cfu/g feed. Granulocyte numbers were significantly higher (P<0.05) in treatment groups in comparison to the control in both the pre- and post-challenge periods. The result suggests that B. subtilis can enhance certain innate immune responses in rohu.