Dietary of Lactobacillus paracasei and Bifidobacterium longum improve nonspecific immune responses, growth performance, and resistance against Vibrio parahaemolyticus in Penaeus vannamei

An In Vitro System Mimics the Intestinal Microbiota of Striped Beakfish (Oplegnathus fasciatus) and Inhibits Vibrio alginolyticus by Limosilactobacillus reuteri-Derived Extracellular Vesicles

Extracellular vesicles (EVs) are functional substances secreted by microbes and host cells, and it has been discovered that they participate in the interactions between different microorganisms. Our recent findings indicate that Limosilactobacillus reuteri-derived EVs have the potential to improve the intestinal microbiota of Oplegnathus fasciatus fish and inhibit pathogenic bacteria. Previous research has reported that the host intestinal cells play a regulatory role in the intestinal microbiota. This suggested that to investigate the mechanisms through which L. reuteri-derived EVs regulate the intestinal microbiota, a system that excludes interference from host intestinal cells should be established. In this study, an in vitro cultured intestinal bacteria system, without host factors, was used to simulate the intestinal microbiota of O. fasciatus fish. After adding L. reuteri-derived EVs to the system, the changes in the microbiota were analyzed. The results showed that L. reuteri-derived EVs effectively reduced the abundance of Vibrio spp. In the results of the in vitro experiments, it was also observed that L. reuteri-derived EVs have the ability to inhibit Vibrio alginolyticus. We further sequenced the small RNA contained in L. reuteri-derived EVs and found that these small RNAs can interfere with genes (LysR, pirin, MIpA/OmpV, CatB, and aspartate-semialdehyde dehydrogenase) related to the growth of V. alginolyticus. Taken together, the results indicate that in the absence of host involvement, the small RNAs present in L. reuteri-derived EVs have the function of inhibiting pathogenic bacteria and exhibit the potential to regulate the intestinal microbiota.

Probiotics for Aquaculture: Hope, Truth, and Reality

The use of microorganisms as beneficial crops for human and animal health has been studied for decades, and these microorganisms have been in practical use for quite some time. Nowadays, in addition to well-known examples of beneficial properties of lactic acid bacteria, bifidobacteria, selected Bacillus spp., and yeasts, there are several other bacteria considered next-generation probiotics that have been proposed to improve host health. Aquaculture is a rapidly growing area that provides sustainable proteins for consumption by humans and other animals. Thus, there is a need to develop new technologies for the production practices associated with cleaner and environment-friendly approaches. It is a well-known fact that proper selection of the optimal probiotics for use in aquaculture is an essential step to ensure effectiveness and safety. In this critical review, we discuss the evaluation of host-specific probiotics in aquaculture, challenges in using probiotics in aquaculture, methods to improve the survival of probiotics under different environmental conditions, technological approach to improving storage, and delivery along with possible negative consequences of using probiotics in aquaculture. A critical analysis of the identified challenges for the use of beneficial microbes in aquaculture will help in sustainable aquafarming, leading to improved agricultural practices with a clear aim to increase protein production.

Antimicrobial Activity, Genetic Relatedness, and Safety Assessment of Potential Probiotic Lactic Acid Bacteria Isolated from a Rearing Tank of Rotifers (Brachionus plicatilis) Used as Live Feed in Fish Larviculture

Aquaculture is a rapidly expanding agri-food industry that faces substantial economic losses due to infectious disease outbreaks, such as bacterial infections. These outbreaks cause disruptions and high mortalities at various stages of the rearing process, especially in the larval stages. Probiotic bacteria are emerging as promising and sustainable alternative or complementary strategies to vaccination and the use of antibiotics in aquaculture. In this study, potential probiotic candidates for larviculture were isolated from a rotifer-rearing tank used as the first live feed for turbot larvae. Two Lacticaseibacillus paracasei and two Lactiplantibacillus plantarum isolates were selected for further characterization due to their wide and strong antimicrobial activity against several ichthyopathogens, both Gram-positive and Gram-negative. An extensive in vitro safety assessment of these four isolates revealed the absence of harmful traits, such as acquired antimicrobial resistance and other virulence factors (i.e., hemolytic and gelatinase activities, bile salt deconjugation, and mucin degradation, as well as PCR detection of biogenic amine production). Moreover, Enterobacterial Repetitive Intergenic Consensus-PCR (ERIC-PCR) analyses unveiled their genetic relatedness, revealing two divergent clusters within each species. To our knowledge, this work reports for the first time the isolation and characterization of Lactic Acid Bacteria (LAB) with potential use as probiotics in aquaculture from rotifer-rearing tanks, which have the potential to optimize turbot larviculture and to introduce novel microbial management approaches for a sustainable aquaculture.

Toxic effects of microplastics and nitrite exposure on intestinal histology, digestion, immunity, and microbial community of shrimp Litopenaeus vannamei

Nitrite and microplastics (MPs) are environmental pollutants that threaten intestinal integrity and affect immune function of shrimp. In this study, the shrimp Litopenaeus vannamei were exposed to the individual and combined stress of nitrite and microplastics for 14 days, and the changes of intestinal histology and physiological functions were investigated. After single and combined stress, affectations occurred in intestinal tissue; the antioxidant enzyme activities (MDA, H2O2, CAT increased) and gene expression levels (CAT, SOD, GPx, HSP70 up-regulated) changed. The expression levels of detoxification genes (CYP450, UGT down-regulated, GST up-regulated), apoptosis genes (CASP-3 up-regulated) and endoplasmic reticulum stress genes (Bip, GRP94 down-regulated) changed. Furthermore, the stress also increased intestinal microbial diversity, causing bacterial composition variation, especially beneficial bacteria and pathogenic bacteria. These results suggested that nitrite and microplastics stress had adverse effects on the intestinal health of L. vannamei by affecting intestinal tissue morphology, immune response and microbial community.

Safety Assessment and Probiotic Potential Comparison of Bifidobacterium longum subsp. infantis BLI-02, Lactobacillus plantarum LPL28, Lactobacillus acidophilus TYCA06, and Lactobacillus paracasei ET-66

Bifidobacterium longum subsp. infantis BLI-02, Lactobacillus paracasei ET-66, Lactobacillus plantarum LPL28, and Lactobacillus acidophilus TYCA06, isolated from healthy breast milk, miso, and the healthy human gut, were assessed for safety in this study. BLI-02, LPL28, TYCA06, and ET-66 exhibited no antibiotic resistance and mutagenic activity in the Ames test at the highest dosage (5000 μg/plate). No genotoxicity was observed in micronucleus and chromosomal aberration assays in rodent spermatogonia at the maximum dosage of 10 g/kg body weight (BW). No acute and sub-chronic toxicity occurred in mice and rats at the maximum tested dosage of 10 g/kg BW and 1.5 g/kg BW, respectively. The lyophilized powder of these strains survived a low pH and high bile salt environment, adhering strongly to Caco-2 cells. Unique antimicrobial activities were noted in these strains, with BLI-02 demonstrating the best growth inhibition against Vibrio parahaemolyticus, LPL28 exhibiting the best growth inhibition against Helicobacter pylori, and ET-66 showing the best growth inhibition against Aggregatibacter actinomycetemcomitans. Based on the present study, the lyophilized powder of these four strains appears to be a safe probiotic supplement at tested dosages. It should be applicable for clinical or healthcare applications.

Lactobacillus rhamnosus Attenuates Cisplatin-Induced Intestinal Mucositis in Mice via Modulating the Gut Microbiota and Improving Intestinal Inflammation

Lactobacillus rhamnosus (LBS) is a well-documented probiotic strain in oncology and has a pivotal role in clinical applications. Here, we have investigated the protective effect of Lactobacillus rhamnosus on intestinal mucositis induced by cisplatin (CP) and explored the underlying mechanisms targeting inflammatory proteins, as well as the histological changes in the intestinal tissue of mice, in addition, the bacterial strains that may be related to the health-enhancing properties. BALB/c mice were pre-treated with or without LBS via oral gavage, followed by mucositis induction with cisplatin. Our results revealed that the LBS-treated groups significantly attenuated proinflammatory cytokine levels (IL-1β, IL-6, and TNF-α) compared to the CP group. Furthermore, LBS mitigated the damaged tight junction integrity caused by CP via up-regulating the levels of claudin, occludin, ZO-1, and mucin-2 protein (MUC-2). Finally, the 16S rRNA fecal microbiome genomic analysis showed that LBS administration enhanced the growth of beneficial bacteria, i.e., Firmicutes and Lachnospiraceae, while the relative abundance of the opportunistic bacteria Bacteroides and Proteobacteria decreased. Collectively, LBS was found to beneficially modulate microbial composition structure and functions and enrich the ecological diversity in the gut.

Lactobacillus plantarum isolated from kefir enhances immune responses and survival of white shrimp (Penaeus vannamei) challenged with Vibrio alginolyticus

Lactobacillus plantarum is known for its probiotics benefit to host, although the effects vary among strains. This study conducted a feeding experiment of three Lactobacillus strains, MRS8, MRS18 and MRS20, which were isolated from kefir and incorporated into the diets of shrimp to evaluate the effects of non-specific immunity, immune-related gene expression, and disease resistance of white shrimp (Penaeus vannamei) against Vibrio alginolyticus. To prepare the experimental feed groups, the basic feed was mixed with different concentrations of L. plantarum strains MRS8, MRS18, and MRS 20, which were incorporated at 0 CFU (control), 1 × 10⁶ CFU (groups 8-6, 18-6, and 20-6), and 1 × 10⁹ CFU (groups 8-9, 18-9, and 20-9) per gram of diet for an in vivo assay. During the rearing period for 28 days of feeding each group, immune responses, namely the total hemocyte count (THC), phagocytic rate (PR), phenoloxidase activity, and respiratory burst were examined on days 0, 1, 4, 7, 14, and 28. The results showed that groups 20-6, 18-9 and 20-9 improved THC, and groups 18-9 and 20-9 improved phenoloxidase activity and respiratory burst as well. The expression of immunity-related genes was also examined. Group 8-9 increased the expression of LGBP, penaeidin 2 (PEN2) and CP, group 18-9 increased the expression of proPO1, ALF, Lysozyme, penaeidin 3 (PEN3) and SOD, and group 20-9 increased the expression of LGBP, ALF, crustin, PEN2, PEN3, penaeidin 4 (PEN4) and CP (p < 0.05). Groups 18-6, 18-9, 2-6, and 20-9 were further used in the challenge test. After feeding for 7 days and 14 days, Vibrio alginolyticus was injected into white shrimp and observed the shrimp survival for 168 h. The results showed that compared to the control, all groups improved the survival rate. Especially, feeding group 18-9 for 14 days improved the survival rate of white shrimp (p < 0.05). After the challenge test for 14 days, the midgut DNA of survival white shrimps was extracted to analyze the colonization of L. plantarum. Among the groups, (6.61 ± 3.58) × 10⁵ CFU/pre shrimp of L. plantarum in feeding group 18-9 and (5.86 ± 2.27) × 10⁵ CFU/pre shrimp in group 20-9 were evaluated by qPCR. Taken together, group 18-9 had the best effects on the non-specific immunity, the immune-related gene expression, and the disease resistance, which might be due to the benefit of the probiotic colonization.

Dietary fulvic acid supplementation improves the growth performance and immune response of sea cucumber (Apostichopus japonicas)

The present study aims to explore the effects of dietary fulvic acid (FA) supplementation on the growth performance, digestive enzyme activity and immune response of sea cucumber (Apostichopus japonicas). FA was used to replace 0 (control), 0.1, 0.5 and 1 g cellulose in the basic diet of sea cucumber to formulate four experimental feeds with equivalent nitrogen and energy denoted as F0, F0.1, F0.3 and F1, respectively. No significant differences were observed in the survival rate among all groups (P > 0.05). Results show that the body weight gain rate, specific growth rate, intestinal trypsin, amylase and lipase activities, serum superoxide dismutase, catalase, lysozyme, alkaline and acid phosphatase activities and disease resistance ability against the pathogen, Vibrio splendidus of the sea cucumbers fed with FA-containing diets were significantly higher than those of the control group (P < 0.05). The optimum dose of dietary FA supplementation required for the maximum growth of sea cucumber was 0.54 g/kg. Therefore, dietary FA supplementation to the feed of sea cucumber can significantly improve its growth performance immune response.

Probiotics Mechanism of Action on Immune Cells and Beneficial Effects on Human Health

Immune cells and commensal microbes in the human intestine constantly communicate with and react to each other in a stable environment in order to maintain healthy immune activities. Immune system-microbiota cross-talk relies on a complex network of pathways that sustain the balance between immune tolerance and immunogenicity. Probiotic bacteria can interact and stimulate intestinal immune cells and commensal microflora to modulate specific immune functions and immune homeostasis. Growing evidence shows that probiotic bacteria present important health-promoting and immunomodulatory properties. Thus, the use of probiotics might represent a promising approach for improving immune system activities. So far, few studies have been reported on the beneficial immune modulatory effect of probiotics. However, many others, which are mainly focused on their metabolic/nutritional properties, have been published. Therefore, the mechanisms behind the interaction between host immune cells and probiotics have only been partially described. The present review aims to collect and summarize the most recent scientific results and the resulting implications of how probiotic bacteria and immune cells interact to improve immune functions. Hence, a description of the currently known immunomodulatory mechanisms of probiotic bacteria in improving the host immune system is provided.