Interactions between candidate probiotics and the immune and antioxidative responses of European sea bass (Dicentrarchus labrax) larvae

Fish skin mucosal surface becomes a barrier of antibiotic resistance genes under apramycin exposure

Antibiotic resistance genes (ARGs) are a kind of emerging environmental contamination, and are commonly found in antibiotic application situations, attracting wide attention. Fish skin mucosal surface (SMS), as the contact interface between fish and water, is the first line of defense against external pollutant invasion. Antibiotics are widely used in aquaculture, and SMS may be exposed to antibiotics. However, what happens to SMS when antibiotics are applied, and whether ARGs are enriched in SMS are not clear. In this study, Zebrafish (Danio rerio) were exposed to antibiotic and antibiotic resistant bacteria in the laboratory to simulate the aquaculture situation, and the effects of SMS on the spread of ARGs were explored. The results showed that SMS maintained the stability of the bacterial abundance and diversity under apramycin (APR) and bacterial exposure effectively. Until 11 days after stopping APR exposure, the abundance of ARGs in SMS (mean value was 3.32 × 10-3 copies/16S rRNA copies) still did not recover to the initial stage before exposure, which means that enriched ARGs in SMS were persistently remained. Moreover, non-specific immunity played an important role in resisting infection of external contamination. Besides, among antioxidant proteins, superoxide dismutase showed the highest activity. Consequently, it showed that SMS became a barrier of antibiotic resistance genes under APR exposure, and ARGs in SMS were difficult to remove once colonized. This study provided a reference for understanding the transmission, enrichment process, and ecological impact of antibiotics and ARGs in aquatic environments.

Current Status of Probiotics in European Sea Bass Aquaculture as One Important Mediterranean and Atlantic Commercial Species: A Review

European sea bass production has increased in recent decades. This increase is associated with an annually rising demand for sea bass, which encourages the aquaculture industries to increase their production to meet that demand. However, this intensification has repercussions on the animals, causing stress that is usually accompanied by dysbiosis, low feed-conversion rates, and immunodepression, among other factors. Therefore, the appearance of pathogenic diseases is common in these industries after immunodepression. Seeking to enhance animal welfare, researchers have focused on alternative approaches such as probiotic application. The use of probiotics in European sea bass production is presented as an ecological, safe, and viable alternative in addition to enhancing different host parameters such as growth performance, feed utilization, immunity, disease resistance, and fish survival against different pathogens through inclusion in fish diets through vectors and/or in water columns. Accordingly, the aim of this review is to present recent research findings on the application of probiotics in European sea bass aquaculture and their effect on growth performance, microbial diversity, enzyme production, immunity, disease resistance, and survival in order to help future research.

In Vitro Characterization of Limosilactobacillus reuteri Lac Ib01 (OL468126.1) Isolated from Traditional Sheep Dry Sausage and Evaluation of the Activity of Arthrospira platensis or Phycocyanin on Its Growth-Promoting Ability

The positive impact of probiotic strains on human health is more evident than ever. To achieve the beneficial health effects and desirable functional properties of probiotics, sufficient numbers of these microorganisms must reach the intestinal tract with high survival rates. The purpose of this study was to identify and characterize a novel strain of Limosilactobacillus reuteri isolated from traditional sheep dry sausage and evaluate its growth-promoting ability with the addition of Arthrospira platensis or phycocyanin extract. In vitro experimental approaches were conducted to determine the physiological features of the candidate probiotic isolate, including biochemical identification, 16S rRNA gene sequencing, tolerance assays to acid and bile salts, antimicrobial activities, adherence ability, and antiproliferative assays. The effects of A. platensis or phycocyanin (0, 1, 5, and 8 mg/mL) on the growth of probiotic cultures were studied after 0, 24, 48, and 72 h. Our results showed that the isolated Limosilactobacillus reuteri (OL468126.1) possesses desirable characteristics as a probiotic candidate and can, therefore, be used as an ingredient in functional foods. Furthermore, A. platensis and phycocyanin extract have great potential for enhancing the growth and prolonging the stationary phase of isolated probiotics. Our findings showed that phycocyanin extract not only plays the role of a natural pigment but also acts as a growth promoter of probiotics.

The Effect of Lactococcus lactis subsp. lactis PTCC 1403 on the Growth Performance, Digestive Enzymes Activity, Antioxidative Status, Immune Response, and Disease Resistance of Rainbow Trout (Oncorhynchus mykiss)

The effect of Lactococcus lactis subsp. lactis strain PTCC 1403 as a potential probiotic was investigated on the growth, hematobiochemical, immune responses, and resistance to Yersinia ruckeri infection in rainbow trout. A total of 240 fish were distributed into 12 fiberglass tanks representing four groups (× 3 replicates). Each tank was stocked with 20 fish (average initial weight: 11.81 ± 0.32 g) and fed L. lactis subsp. lactis PTCC 1403 at 0 (control, T0), 1 × 10⁹ (T1), 2 × 10⁹ (T2), and 3 × 10⁹ (T3) CFU/g feed for 8 weeks. The results showed enhanced protein efficiency ratio and reduced feed conversion ratio in the fish-fed T2 diet. Further, fish-fed T2 and T3 diets showed a significantly higher survival rate than the control (p < 0.05). Trypsin, lipase, and protease activities were increased in fish-fed L. lactis subsp. lactis PTCC 1403 compared to the control (p < 0.05). Fish fed with a T2 diet showed significantly (p < 0.05) lower glucose content than other groups. The blood lysozyme activity and IgM showed significantly (p < 0.05) higher values in fish-fed T2 and T3 diets than in other groups. The antioxidative responses were increased in fish-fed T2 and T3 diets (p < 0.05). After 7 days post-Y. ruckeri challenge, the cumulative mortality rate showed the lowest value in fish fed with T1 and T2 diets, while the highest value was recorded in the control group. In conclusion, the results revealed beneficial effects of L. lactis subsp. lactis PTCC 1403 on the feed efficiency, immune response, and resistance to Y. ruckeri infection in rainbow trout.

Dietary administration effects of exopolysaccharide from potential probiotic strains on immune and antioxidant status and nutritional value of European sea bass (Dicentrarchus labrax L.)

The use of biological immunostimulants is considered a valuable practice to improve culture conditions in aquaculture sector that may help to increase production and maintain healthy environment. We undertook this study in order to evaluate the potential effect of the administration of two exopolysaccharides (EPS) "EPLB" and "EPB" derived from potential probiotic strains on immune and antioxidant status of European sea bass (Dicentrarchus labrax L.) larvae. In order to find out if the EPSs have an effect on the biochemical composition during the trial period, the nutritional value has been evaluated. The results revealed that expression levels of immune-relevant genes (infg, Il1b, Il8, Il6 and tcr-β) in the gut and head kidney and the scavenging enzymes (cat, sod, gr) genes in the liver were modulated. In fact, the dietary supplementation with the tested EPSs, significantly enhances the expression of immune-associated genes in the head-kidney, particularly infg and tcrβ, as well as catalase gene in liver. During the period of study, EPSs administration did not affect the fatty acid profiles of larvae, which is balanced. This is confirmed by the Docosahexaenoic acid / Eicosapentaenoic acid ratio and demonstrates that EPLB and EPB can be administrated without any negative effect on biochemical composition of European sea bass. The present findings provided evidence that the tested EPSs with antibacterial and antioxidant activities can enhance immune response without negative effect on the biochemical composition. The used EPSs can be considered as a good source of natural functional aquafeed ingredients for European sea bass.

Comparative study of host-associated and commercial probiotic effects on serum and mucosal immune parameters, intestinal microbiota, digestive enzymes activity and growth performance of roach (Rutilus rutilus caspicus) fingerlings

The study aimed to isolate host-associated probiotic (HAP) lactic acid bacteria from intestine of adult Caspian roach and compare the efficacy of HAP with a commercially available probiotic strain (Pediococcus acidilactici) on the growth and feed utilisation, digestive enzymes and systemic and mucosal immune system of roach fingerling. The HAP strain isolated from roach intestine was Enterococcus faecium strain CGMCC1.2136. The experiment was a simple completely randomized design and lasted for eight weeks. Two hundred and seventy fish with an average weight of 12 g randomly distributed into nine tanks. The trial consisted of three treatments with three respective replications. During the experimental period, fish received basal diet without any bacterial supplementation (as the control group), basal diet enriched with 10⁸ CFU g^-1 HAP or 10⁷ CFU g^-1 CP. At the end of the experiment, serum immune parameters of those fish fed HAP including alkaline phosphatase activity, total protein content, total immunoglobulin level, lysozyme activity and complement activity (ACH50) were significantly higher that other experimental groups (P < 0.05). Similarly, dietary supplementation of HAP resulted in better mucosal immune parameters in comparison to control group and commercial probiotic administration (P < 0.05). Intestinal heterotrophic bacteria and autochthonous LAB counts of those fish fed HAP were significantly higher than other experimental groups at the end of the experiment as well as 15 days seizing probiotic administrations (P < 0.05). Fish fed with HAP containing diet presented significantly higher amylase, lipase and protease activity in comparison to the CP fed fish and the control group (P < 0.05). Growth indices of those fish fed HAP were significantly higher than other treatments (P < 0.05). The highest carcass protein and ash content along with the lowest body moisture content belonged to those fish received HAP (P < 0.05). In conclusion, the use host-HAP resulted in better immune competence and growth performance and it seems aquaculture sector should probably focus on the development of probiotics isolated from the cultured species instead of using terrestrial probiotics with greatly different requirements and environmental conditions.

Influence of Dietary Supplementation of Probiotic Pediococcus acidilactici MA18/5M During the Transition From Freshwater to Seawater on Intestinal Health and Microbiota of Atlantic Salmon (Salmo salar L.)

The aim of this study was to assess the effect of the transfer from freshwater to seawater on the distal intestinal bacterial communities of Atlantic salmon (Salmo salar L.) and to evaluate the effect of dietary inclusion of Pediococcus acidilactici MA18/5M (at 1.19 × 10⁶ CFU/g). In this context, fish health and antiviral response were also investigated. A 12-week feeding trial was conducted in a flow-through rearing system involving 6 weeks in freshwater and 6 weeks in seawater. Fish received a control and probiotic diet. The composition of the salmon gut bacterial communities was determined by high-throughput sequencing of digesta and mucosa samples from both the freshwater and seawater stage. The main phyla detected during both freshwater and seawater stages were Firmicutes, Proteobacteria, Fusobacteria, and Actinobacteria. Significant differences were observed between the intestinal microbiota in the digesta and the mucosa. Both probiotic supplementation and the seawater transfer (SWT) had a substantial impact on the microbial communities, with most pronounced changes detected in the mucosal communities after SWT. This last finding together with a significantly higher antiviral response (mx-1 and tlr3 gene expression) in the distal intestine of fish fed the probiotic diet suggest a causal link between the microbiota modulation and activation of antiviral response. Feeding probiotics during the freshwater stage did not significantly increase survival after infectious pancreatic necrosis virus (IPNV) challenge after SWT, although higher survival was observed in one out of two replicate challenge tanks. In conclusion, this study demonstrated that both dietary probiotic supplementation and transfer from freshwater to seawater have an important role in modulating the bacterial communities in the distal intestine of Atlantic salmon. Furthermore, supplementation of the diet with P. acidilactici MA18/5M can modulate antiviral response.

Skin-associated lactic acid bacteria from North American bullfrogs as potential control agents of Batrachochytrium dendrobatidis

The fungal pathogen Batrachochytrium dendrobatidis (Bd) is the causative agent of chytridiomycosis and has been a key driver in the catastrophic decline of amphibians globally. While many strategies have been proposed to mitigate Bd outbreaks, few have been successful. In recent years, the use of probiotic formulations that protect an amphibian host by killing or inhibiting Bd have shown promise as an effective chytridiomycosis control strategy. The North American bullfrog (Lithobates catesbeianus) is a common carrier of Bd and harbours a diverse skin microbiota that includes lactic acid bacteria (LAB), a microbial group containing species classified as safe and conferring host benefits. We investigated beneficial/probiotic properties: anti-Bd activity, and adhesion and colonisation characteristics (hydrophobicity, biofilm formation and exopolysaccharide-EPS production) in two confirmed LAB (cLAB-Enterococcus gallinarum CRL 1826, Lactococcus garvieae CRL 1828) and 60 presumptive LAB (pLAB) [together named as LABs] isolated from bullfrog skin.We challenged LABs against eight genetically diverse Bd isolates and found that 32% of the LABs inhibited at least one Bd isolate with varying rates of inhibition. Thus, we established a score of sensitivity from highest (BdGPL AVS7) to lowest (BdGPL C2A) for the studied Bd isolates. We further reveal key factors underlying host adhesion and colonisation of LABs. Specifically, 90.3% of LABs exhibited hydrophilic properties that may promote adhesion to the cutaneous mucus, with the remaining isolates (9.7%) being hydrophobic in nature with a surface polarity compatible with colonisation of acidic, basic or both substrate types. We also found that 59.7% of LABs showed EPS synthesis and 66.1% produced biofilm at different levels: 21% weak, 29% moderate, and 16.1% strong. Together all these properties enhance colonisation of the host surface (mucus or epithelial cells) and may confer protective benefits against Bd through competitive exclusion. Correspondence analysis indicated that biofilm synthesis was LABs specific with high aggregating bacteria correlating with strong biofilm producers, and EPS producers being correlated to negative biofilm producing LABs. We performed Random Amplified Polymorphic DNA (RAPD)-PCR analysis and demonstrated a higher degree of genetic diversity among rod-shaped pLAB than cocci. Based on the LAB genetic analysis and specific probiotic selection criteria that involve beneficial properties, we sequenced 16 pLAB which were identified as Pediococcus pentosaceus, Enterococcus thailandicus, Lactobacillus pentosus/L. plantarum, L. brevis, and L. curvatus. Compatibility assays performed with cLAB and the 16 species described above indicate that all tested LAB can be included in a mixed probiotic formula. Based on our analyses, we suggest that E. gallinarum CRL 1826, L. garvieae CRL 1828, and P. pentosaceus 15 and 18B represent optimal probiotic candidates for Bd control and mitigation.

Gut Bacterial Communities in Geographically Distant Populations of Farmed Sea Bream (Sparus aurata) and Sea Bass (Dicentrarchus labrax)

This study investigated the profile of the autochthonous gut bacterial communities in adult individuals of Sparus aurata and Dicentrarchus labrax reared in sea cages in five distantly located aquaculture farms in Greece and determine the impact of geographic location on them in order to detect the core gut microbiota of these commercially important fish species. Data analyses resulted in no significant geographic impact in the gut microbial communities within the two host species, while strong similarities between them were also present. Our survey revealed the existence of a core gut microbiota within and between the two host species independent of diet and geographic location consisting of the Delftia, Pseudomonas, Pelomonas, Propionibacterium, and Atopostipes genera.

The effects of single or combined administration of galactooligosaccharide and Pediococcus acidilactici on cutaneous mucus immune parameters, humoral immune responses and immune related genes expression in common carp (Cyprinus carpio) fingerlings

The present study was performed to investigate the effects of single or combined administration of galactooligosaccharide (GOS) and Pediococcus acidilactici on cutaneous mucus immune parameters, humoral immune responses and immune related genes expression in common carp (Cyprinus carpio) fingerlings. Carps were fed experimental diets for 8 weeks as follows: non-supplemented (Control), prebiotic diet (10 g/kg GOS), probiotic diet (1 g/kg [0.9 × 10⁷ CFU] lyophilized P. acidilactici) and synbiotic diet (10 GOS in combination with 1 g/kg [0.9 × 10⁷ CFU] lyophilized P. acidilactici). Unlike skin mucus, the serum lysozyme activity showed no significant difference between carps fed supplemented or control diets, however, remarkable elevation of serum ACH50 activity was noticed in carps fed supplemented diet (pro-, pre- and synbiotic diets) compared control group. Besides, feeding on pro-, pre- and synbiotic supplemented diets significantly increased serum and skin mucus total Ig levels. However, no significant difference was observed between treatments and control group in case of skin mucus proteases activity. There was no significant difference between expression levels of intestinal genes of LYZ and IL1b in fish fed on pre- and synbiotic, compared to the control. However, evaluation of TNF-alpha gene expression in the intestine of carps revealed remarkable down-regulation in treated groups (p < 0.05). These results indicated positive effect of supplementation of carp diet with GOS and P. acidilactici on some mucosal or serum immune parameters.

Apple cider vinegar boosted immunomodulatory and health promoting effects of Lactobacillus casei in common carp (Cyprinus carpio)

The present study was performed to investigate the immunomodulatory and health promoting effects of combined or singular administration of apple cider vinegar (ACV) and Lactobacillus casei in common carp (Cyprinus carpio) diet. An 8-week feeding trial was designed with following treatments: Control (basal diet), Pro (contains 10⁷ CFU g^-1L. casei), LACV (contains 1% ACV), HACV (contains 2% ACV), Pro + LACV (contains 10⁷ CFU g^-1L. casei plus 1% ACV) and Pro + HACV (contains 10⁷ CFU g^-1L. casei plus 2% ACV). Evaluation of skin mucus revealed notable increase of total Ig level and lysozyme activity in Pro + LACV and Pro + HACV treatments compared other groups (P < 0.05). Similarly, serum total Ig and lysozyme activity in HACV, Pro + LACV and Pro + HACV fed carps was remarkably higher than other groups (P < 0.05). However, regarding serum alternative complement (ACH50) activity significant difference was observed just between Pro + HACV and control treatment (P < 0.05). The highest expression of immune related (LYZ, TNF-alpha, IL1b, IL8) and antioxidant enzymes genes (GSR, GST) were observed in carps fed Pro + HACV and Pro + LACV. The expression of GH gene expression in Pro, LACV and HACV treatments was significantly higher than those in control group (P < 0.05). The highest expression level of GH and IGF1 was observed in fish fed combined Pro and ACV (P < 0.05). These results indicated that co-administration of ACV boosted immunomodulatory and health promoting effects of L. casei and can be considered as a promising immunostimulants in early stage of common carp culture.

Dietary Lactobacillus acidophilus modulated skin mucus protein profile, immune and appetite genes expression in gold fish (Carassius auratus gibelio)

The objective of the present study was to investigate the effect of dietary Lactobacillus acidophilus on skin mucus protein pattern, immune and appetite related genes expression as well as growth performance in gold fish (Carassius auratus gibelio). Three hundred healthy gold fish (2.5 ± 0.05) juveniles were randomly distributed in 12 glass aquariums (400-L; 25 fish per aquaria) and fed experimental diets contain different levels of L. acidophilus (0, 1.5 × 10⁸, 3 × 10⁸ and 6 × 10⁸) for 8 weeks. SDS-PAGE analysis of skin mucus protein profile at the end of the feeding trial revealed differences in protein profile of probiotic fed fish and control group; even three new bands were observed in L. acidophilus treated groups. Furthermore, fish fed 6 × 10⁸ CFU g^-1 supplemented diet showed up-regulation of both TNF-1α and TNF-2α gene expression (P < 0.05). Evaluation of appetite related gene expression showed down-regulation of ghrelin in probiotic fed fish compared those of control treatment (P < 0.05). However, administration of different levels of L. acidophilus had no significant effects on growth performance (P > 0.05). These results demonstrated that while no beneficial effects on growth performance, dietary L. acidophilus affects immune and appetite related genes expression as well as skin mucus protein profile.