Phenyl-lactic acid is an active ingredientin bactericidal supernatants of Lactobacillus crispatus

Anti-fungal effects of lactic acid bacteria from pickles on the growth and sterigmatocystin production of Aspergillus versicolor

Sterigmatocystin (STC) is an emerging mycotoxin that poses a significant threat to the food security of cereal crops. To mitigate STC contamination in maize, this study employed selected lactic acid bacteria as biocontrol agents against Aspergillus versicolor, evaluating their biocontrol potential and analyzing the underlying mechanisms. Lactiplantibacillus plantarum HJ10, isolated from pickle, exhibited substantial in vitro antifungal activity and passed safety assessments, including antibiotic resistance and hemolysis tests. In vivo experiments demonstrated that L. plantarum HJ10 significantly reduced the contents of A. versicolor and STC in maize (both >84 %). The impact of heat, enzymes, alkali, and other treatments on the antifungal activity of cell-free supernatant (CFS) was investigated. Integrated ultra-high-performance liquid chromatography (UPLC) and gas chromatography-mass spectrometry (GC-MS) analysis revealed that lactic acid, acetic acid, and formic acid are the key substances responsible for the in vitro antifungal activity of L. plantarum HJ10. These metabolites induced mold apoptosis by disrupting cell wall structure, increasing cell membrane fluidity, reducing enzyme activities, and disrupting energy metabolism. However, in vivo antagonism by L. plantarum HJ10 primarily occurs through organic acid production and competition for growth space and nutrients. This study highlights the potential of L. plantarum HJ10 in reducing A. versicolor and STC contamination in maize.

The evolving world of the urinary microbiome

PURPOSE OF REVIEW

The existence of urinary microbiome in healthy individuals is now widely accepted as the longstanding belief in urinary tract sterility was disproved over a decade ago. The urinary microbiome has since been implicated in multiple urologic conditions including urinary tract infection (UTI), urinary incontinence, and bladder cancer. This review relays new findings of urinary microbiome compositional changes associated with aging and UTI susceptibility.

RECENT FINDINGS

Recent advancements have established how the urinary microbiome changes over the lifespan. Studies finding distinct urinary microbiomes in prepubescent, reproductive age, and postmenopausal females have identified sex hormones as potential modulators of urinary microbiome composition and have identified prevalent species that may be markers of dysbiosis. Research in male children finds a cultivable urinary microbiota that varies with age or urologic history but not delivery mode. Emerging research also addresses the function of the urinary microbiota, including genetic factors associated with urinary tract colonization and interactions with uropathogens.

SUMMARY

The urinary microbiome is a promising therapeutic target for urologic disease. However, a more functional understanding is necessary for the development of microbiome-based therapies. Future research should develop accurate animal models and explore functional relationships between the urinary microbiome and the host environment.

Draft genome sequences of three Lactobacillus crispatus strains, isolated from the female urinary tract

Lactobacillus crispatus is a frequent member of the female urogenital microbiota. Here, we present the draft genome assemblies of three L. crispatus strains: UMB4356, UMB5661, and UMB6244. All strains were isolated from voided urine samples from females with type 2 diabetes.

Evidence of Lactobacillus strains shared between the female urinary and vaginal microbiota

Lactobacillus species are common inhabitants of the 'healthy' female urinary and vaginal communities, often associated with a lack of symptoms in both anatomical sites. Given identification by prior studies of similar bacterial species in both communities, it has been hypothesized that the two microbiotas are in fact connected. Here, we carried out whole-genome sequencing of 49 Lactobacillus strains, including 16 paired urogenital samples from the same participant. These strains represent five different Lactobacillus species: L. crispatus, L. gasseri, L. iners, L. jensenii, and L. paragasseri. Average nucleotide identity (ANI), alignment, single-nucleotide polymorphism (SNP), and CRISPR comparisons between strains from the same participant were performed. We conducted simulations of genome assemblies and ANI comparisons and present a statistical method to distinguish between unrelated, related, and identical strains. We found that 50 % of the paired samples have identical strains, evidence that the urinary and vaginal communities are connected. Additionally, we found evidence of strains sharing a common ancestor. These results establish that microbial sharing between the urinary tract and vagina is not limited to uropathogens. Knowledge that these two anatomical sites can share lactobacilli in females can inform future clinical approaches.

Synthesis of current pediatric urinary microbiome research

The human urinary bladder hosts a complex microbial community of low biomass referred to as the urobiome. While the composition of the urobiome has been investigated in adults for over a decade now, only a few studies have considered the presence and composition of the urobiome in children. It is critical to explore how the urobiome develops throughout the life span and how it changes in the presence of various health conditions. Therefore, we set to review the available data on pediatric urobiome composition and its development with age and disease. In addition, we focused on identifying and reporting specific gaps in our knowledge of the pediatric urobiome that we hope will be addressed by future studies in this swiftly developing field with fast-improving methods and consensus.

Development of phenyllactic acid ionic liquids and evaluation of cytotoxicity to human cervical epithelial cells

Phenyllactic acid (PLA), is a naturally produced, broad-spectrum antimicrobial compound with activity against bacteria and fungi. PLA can be produced by a variety of lactic acid bacteria, including vaginal Lactobacillus species, which are healthy constituents of the vaginal microbiome with a protective role against invading pathogenic bacteria and/or fungi. Additionally, PLA has been shown to exhibit anti-inflammatory and immunomodulatory properties, overall indicating its therapeutic potential as an intravaginally delivered compound for modulation of the vaginal microbiome. However, PLA has low kinetic solubility in water. Hence, strategies to improve the solubility of PLA are necessary to facilitate its intravaginal delivery. Using biocompatible cations, choline and carnitine, we successfully transformed both d- and l-enantiomers of crystalline PLA into amorphous low-melting ionic liquids (ILs) with high water solubility. We further evaluated the in vitro cytotoxicity of PLA ILs to human cervical epithelial cells. Microscopic visualisation of cellular morphology using crystal violet staining and MTT cell proliferation assay revealed that PLA ILs result in minimal morphological changes and low cytotoxicity to human cervical epithelial cells. Overall, we successfully demonstrated that transforming PLA into ILs efficiently enhances its solubility in water and these formulations are not toxic to human epithelial cells. This investigation lays the groundwork for future testing of PLA ILs for their antimicrobial properties and metabolic activity within the cervicovaginal microenvironment.

The larvicidal effect of the supernatant of Lactobacillus acidophilus ATCC 4356 on Toxocara canis

Human toxocariasis is a parasitic anthropozoonosis that is difficult to treat and control. A previous study carried out with Lactobacillus acidophilus ATCC 4356 revealed that the cell free supernatant (CFS) of this probiotic killed 100% of Toxocara canis larvae in vitro. The present study aimed to investigate the characteristics of the CFS of L. acidophilus ATCC 4356, which may be involved in its larvicidal effects on T. canis. L. acidophilus ATCC 4356 was cultured, and lactic and acetic acids present in the CFS were quantified by high performance liquid chromatography (HPLC). The levels of pH and H2O2 were also analyzed. To assess the larvicidal effect of the CFS, this was tested pure and diluted (1:2 to 1:128) on T. canis larvae. High concentrations of lactic and acetic acids were detected in the CFS. The acidity of the pure CFS was observed at pH 3.8, remaining acidic at dilutions of 1:2 to 1:16. Regarding the in vitro larvicidal effect, 100% death of T. canis larvae was observed using the pure CFS and 1:2 dilution. Based on these results, it can be inferred that the presence of higher concentrations of organic acids and low pH of the medium contributed to the larvicidal activity of the CFS of L. acidophilus ATCC 4356. In addition, the maintenance of the larvicidal effect, even after dilution, suggests a greater chance of the larvicidal effect of this CFS against T. canis in vivo.

The modulatory effect of Lactobacillus gasseri ATCC 33323 on autophagy induced by extracellular vesicles of Helicobacter pylori in gastric epithelial cells in vitro

Helicobacter pylori has been recognized as a true pathogen, which is associated with various gastroduodenal diseases, and gastric adenocarcinoma. The crosstalk between H. pylori virulence factors and host autophagy remains challenging. H. pylori can produce extracellular vesicles (EVs) that contribute to gastric inflammation and malignancy. Some probiotic strains have been documented to modulate cell autophagy process. This study was aimed to investigate the modulatory effect of cell-free supernatant (CFS) obtained from Lactobacillus gasseri ATCC 33323 on autophagy induced by H. pylori-derived EVs. EVs were isolated from two clinical H. pylori strains (BY-1 and OC824), and characterized using transmission electron microscopy (TEM) and dynamic light scattering (DLS). The viability of AGS cells was assessed after exposure to different concentrations of H. pylori EVs, and L. gasseri CFS. Based on MTT assay and Annexin V-FITC/PI staining, 50 μg/ml of H. pylori EVs and 10 % v/v of L. gasseri CFS were used for further cell treatment experiments. Autophagy was examined using acridin orange (AO) staining, RT-qPCR analysis for autophagy mediators (LC3B, ATG5, ATG12, ATG16L1, BECN1, MTOR, and NOD1), and western blotting for LC3B expression. H. pylori EVs were detected to range in size from 50 to 200 nm. EVs of both H. pylori strains and L. gasseri CFS showed no significant effect on cell viability as compared to untreated cells. H. pylori EVs promoted the development of acidic vesicular organelles and the expression of autophagy-related genes (LC3B, ATG5, ATG12, ATG16L1, BECN1, and NOD1), and decreased the expression of MTOR in AGS cells at 12 and 24 h time periods. In addition, the production of LC3B was increased following 12 h of treatment in AGS cells. In contrast, L. gasseri CFS effectively inhibited EVs-induced autophagy, as evidenced by reduced acidic vesicular organelle formation and modulation of autophagy markers. Our study indicated that L. gasseri CFS can effectively suppress H. pylori EV-induced autophagy in AGS cells. Further investigations are required to decipher the mechanism of action L. gasseri CFS and its metabolites on autophagy inhibition induced by H. pylori.

Prophylactic application of vaginal lactic acid bacteria against urogenital pathogens and its prospective use in sanitary suppositories

Beneficial and pathogenic microbes coexist in the vaginal canal, where a diminishing population of lactic acid bacteria may cause recurring urogenital infections. Probiotic bacteria Lactobacillus crispatus, Lactobacillus gasseri, Lactobacillus vaginalis, and pathogenic microbes Enterococcus faecalis, Enterobacter cloacae, Shigella sp., Staphylococcus epidermidis, and Escherichia fergusonii were isolated from vaginal swabs. Lactobacillus sp. and their probiotic culture free supernatant (PCFS) inhibited the growth of the above-mentioned urogenital pathogens. L. crispatus produced both lactic acid and hydrogen peroxide, exhibiting the best antimicrobial potential against the studied pathogens. Lyophilized L. crispatus had a shelf life of 12 months and the lyophilized PCFS also retained its antibacterial property with a minimum inhibition concentration of 1 μg/μL. Carboxy-methyl cellulose-alginate, a green alternative to super-absorbent polymers, was encapsulated with L. crispatus cells. The probiotic in its encapsulated state retained its viability for 21 days, and the bead showed 30% solvent absorptive capacity. PCFS-laced non-woven fabric displayed antibacterial property with no change in its physicochemical properties. These probiotic and postbiotic formulations have excellent prophylactic potential for urogenital infections. Such formulations can be exploited as additives in sanitary suppositories to enhance vaginal health.

Urine microbiome in individuals with an impaired immune system

With the advent of next generation sequencing, it is now appreciated that human urine is not sterile. Recent investigations of the urinary microbiome (urobiome) have provided insights into several urological diseases. Urobiome dysbiosis, defined as non-optimal urine microbiome composition, has been observed in many disorders; however, it is not clear whether this dysbiosis is the cause of urinary tract disorders or a consequence. In addition, immunologically altered disorders are associated with higher rates of urinary tract infections. These disorders include immunoproliferative and immunodeficiency diseases, cancer, and immunosuppressant therapy in transplant recipients. In this review, we examine the current state of knowledge of the urobiome in immunologically altered diseases, its composition and metabolomic consequences. We conclude that more data are required to describe the urobiome in immune altered states, knowledge that could facilitate understanding the role of the urobiome and its pathophysiological effects on urinary tract infections and other disorders of the urinary tract.

Fusarium biocontrol: antagonism and mycotoxin elimination by lactic acid bacteria

Mycotoxins produced by Fusarium species are secondary metabolites with low molecular weight formed by filamentous fungi generally resistant to different environmental factors and, therefore, undergo slow degradation. Contamination by Fusarium mycotoxins in cereals and millets is the foremost quality challenge the food and feed industry faces across the globe. Several types of chemical preservatives are employed in the mitigation process of these mycotoxins, and they help in long-term storage; however, chemical preservatives can be used only to some extent, so the complete elimination of toxins from foods is still a herculean task. The growing demand for green-labeled food drives to evade the use of chemicals in the production processes is getting much demand. Thus, the biocontrol of food toxins is important in the developing food sector. Fusarium mycotoxins are world-spread contaminants naturally occurring in commodities, food, and feed. The major mycotoxins Fusarium species produce are deoxynivalenol, fumonisins, zearalenone, and T2/HT2 toxins. Lactic acid bacteria (LAB), generally regarded as safe (GRAS), is a well-explored bacterial community in food preparations and preservation for ages. Recent research suggests that LAB are the best choice for extenuating Fusarium mycotoxins. Apart from Fusarium mycotoxins, this review focuses on the latest studies on the mechanisms of how LAB effectively detoxify and remove these mycotoxins through their various bioactive molecules and background information of these molecules.

Use of probiotic lactobacilli in the treatment of vaginal infections: In vitro and in vivo investigations

The vaginal microbiome is a distinct component of the human microbiome that is colonized by a wide variety of microorganisms. Lactobacilli are the most frequently identified microorganisms in the healthy human vagina. These Gram-positive bacilli can acidify the vaginal microenvironment, inhibit the proliferation of other pathogenic microorganisms, and promote the maintenance of a eubiotic vaginal microbiome. However, a vaginal flora with a reduced proportion or abundance of lactobacilli is associated with various vaginal infections that have been linked to serious health consequences such as infertility, preterm birth, pelvic inflammatory disease, premature rupture of membranes, and miscarriage. Due to their “Generally Recognized as Safe” classification and critical role in vaginal health, probiotic lactobacilli have been widely used as an alternative or adjunct to traditional antibiotic therapy for the treatment of vaginal infections and restoration of the vaginal microbiome. This review focuses on the significant role of probiotic lactobacilli in the vaginal microenvironment and discusses the use of probiotic lactobacilli in the treatment of female vaginal infections in vitro and in vivo.

Effect of Alcaligenes sp. on corrosion behavior of X65 steel in simulated offshore oilfield-produced water

In this paper, the effect of Alcaligenes sp. on the corrosion process of X65 steel was investigated by using non-targeted metabolomics techniques for comprehensive characterization of metabolites, combined with surface analysis techniques and electrochemical testing. The results showed that the organic acids produced by Alcaligenes sp. accelerated the corrosion process of X65 steel in the early stage, and the presence of Alcaligenes sp. promoted the deposition of stable corrosion products and minerals in the middle and late stages. In addition, proteoglycans and corrosion inhibiting substances were enriched on the metal surface, which enhanced the stability of the film. The combined effect of multiple factors makes the mixed film of biofilm and corrosion products more dense and complete, which effectively inhibits the corrosion of X65 steel.

Commensal Lactobacilli Metabolically Contribute to Cervical Epithelial Homeostasis in a Species-Specific Manner

In reproductive-age women, the vaginal microbiome is typically dominated by one or a few Lactobacillus species, including Lactobacillus crispatus, Lactobacillus iners, Lactobacillus paragasseri, Lactobacillus mulieris, and Lactobaccillus crispatus, has been associated with optimal cervicovaginal health; however, much is still unknown about how other lactobacilli metabolically contribute to cervicovaginal health. We hypothesized that metabolites of each Lactobacillus species differ and uniquely contribute to health and homeostasis. To address this hypothesis, we utilized a human three-dimensional (3D) cervical epithelial cell model in conjunction with genomics analyses and untargeted metabolomics to determine the metabolic contributions of less-studied vaginal lactobacilli-L. iners, L. paragasseri, and L. mulieris. Our study validated that vaginal lactobacilli exhibit a close phylogenetic relationship. Genomic findings from publicly available strains and those used in our study indicated that L. iners is metabolically distinct from other species of lactobacilli, likely due to a reduced genome size. Lactobacilli and mock controls were distinguishable based on global metabolic profiles. We identified 95 significantly altered metabolites (P < 0.05) between individual lactobacilli and mock controls. Metabolites related to amino acid metabolism were shared among the lactobacilli. N-Acetylated amino acids with potential antimicrobial properties were significantly elevated in a species-specific manner. L. paragasseri and L. iners shared aromatic, but not carbohydrate-derived, lactic acid metabolites with potential antimicrobial properties that may contribute to homeostasis of the cervicovaginal environment. Additionally, L. iners uniquely altered lipid metabolism, which may be a sign of adaptation to the cervicovaginal niche. Overall, these findings further elucidate the metabolic contributions of three key vaginal Lactobacillus species in gynecological health. IMPORTANCE Lactobacillus species contribute to cervicovaginal health by their production of lactic acid and other antimicrobial compounds. Yet, much is still unknown regarding the metabolic potential of lesser-studied but common vaginal lactobacilli. Here, we used untargeted metabolomics coupled with our 3D cervical epithelial cell model to identify metabolic differences among vaginal Lactobacillus species (Lactobacillus iners, Lactobacillus paragasseri, and Lactobacillus mulieris) and how those differences related to maintaining homeostasis of the cervical epithelium. Human 3D cell models are essential tools for studying host-bacteria interactions and reducing confounding factors inherent in clinical studies. Therefore, these unique models allowed us to decipher the putative lactobacilli mechanisms that contribute to their roles in health or disease. Metabolic analyses revealed distinct profiles of each Lactobacillus species but also shared metabolic contributions associated with antimicrobial activity: amino acid metabolism, N-acetylated amino acids, and aromatic lactic acids. These patterns provided validation of metabolites associated with health in clinical studies and provided novel targets, including immunomodulatory and antimicrobial metabolites, for postbiotic therapies.

Coenzyme self-sufficiency system-recent advances in microbial production of high-value chemical phenyllactic acid

Phenyllactic acid (PLA), a natural antimicrobial substance, has many potential applications in the food, animal feed, pharmaceutical and cosmetic industries. However, its production is limited by the complex reaction steps involved in its chemical synthesis. Through advances in metabolic engineering and synthetic biology strategies, enzymatic or whole-cell catalysis was developed as an alternative method for PLA production. Herein, we review recent developments in metabolic engineering and synthetic biology strategies that promote the microbial production of high-value PLA. Specially, the advantages and disadvantages of the using of the three kinds of substrates, which includes phenylpyruvate, phenylalanine and glucose as starting materials by natural or engineered microbes is summarized. Notably, the bio-conversion of PLA often requires the consumption of expensive coenzyme NADH. To overcome the issues of NADH regeneration, efficiently internal cofactor regeneration systems constructed by co-expressing different enzyme combinations composed of lactate dehydrogenase with others for enhancing the PLA production, as well as their possible improvements, are discussed. In particular, the construction of fusion proteins with different linkers can achieve higher PLA yield and more efficient cofactor regeneration than that of multi-enzyme co-expression. Overall, this review provides a comprehensive overview of PLA biosynthesis pathways and strategies for increasing PLA yield through biotechnology, providing future directions for the large-scale commercial production of PLA and the expansion of downstream applications.

Recurrent urinary tract infection and estrogen shape the taxonomic ecology and function of the postmenopausal urogenital microbiome

Postmenopausal women are severely affected by recurrent urinary tract infection (rUTI). The urogenital microbiome is a key component of the urinary environment. However, changes in the urogenital microbiome underlying rUTI susceptibility are unknown. Here, we perform shotgun metagenomics and advanced culture on urine from a controlled cohort of postmenopausal women to identify urogenital microbiome compositional and function changes linked to rUTI susceptibility. We identify candidate taxonomic biomarkers of rUTI susceptibility in postmenopausal women and an enrichment of lactobacilli in postmenopausal women taking estrogen hormone therapy. We find robust correlations between Bifidobacterium and Lactobacillus and urinary estrogens in women without urinary tract infection (UTI) history. Functional analyses reveal distinct metabolic and antimicrobial resistance gene (ARG) signatures associated with rUTI. Importantly, we find that ARGs are enriched in the urogenital microbiomes of women with rUTI history independent of current UTI status. Our data suggest that rUTI and estrogen shape the urogenital microbiome in postmenopausal women.

Lactobacillus crispatus-derived exopolysaccharides with antibacterial activity limit Salmonella typhimurium invasion by inhibiting inflammasome-mediated pyroptosis

In this study, a novel heteropolysaccharide (EPS 7-4) with a molecular weight of 53 387 Da was isolated from Lactobacillus crispatus, and it was mainly composed of mannose (36.9%) and glucose (30.8%). EPS 7-4 showed excellent inhibitory effects on the proliferation, biofilm formation, and virulence factor gene expression of Salmonella typhimurium (S. typhimurium) by disrupting the integrity of the bacterial wall. Furthermore, EPS 7-4 can effectively restrict bacterial translocation, upregulate the abundance of Lactobacillus spp. and Bifidobacterium spp., and alleviate the S. typhimurium induced severe inflammatory response in the intestinal tract of mice. Besides, we demonstrated that EPS 7-4 can protect mice by inhibiting S. typhimurium induced pyroptosis, with the mechanism that EPS 7-4 affects ASC oligomerization during inflammasome-mediated pyroptosis. Therefore, due to its excellent anti-bacterial and anti-inflammatory abilities, EPS 7-4 is a promising health regulator owing to its excellent antibacterial and anti-inflammatory abilities.

Commensal Urinary Lactobacilli Inhibit Major Uropathogens In Vitro With Heterogeneity at Species and Strain Level

The human urinary microbiome is thought to affect the development and progression of urinary tract infections (UTI), particularly recurrent UTIs in aging populations of women. To understand the possible interactions of urinary pathogens with commensal bacteria inhabiting the aging bladder, we conducted an initial functional assessment of a representative set of urinary lactobacilli that dominate this niche in postmenopausal women. We created a repository of urinary bladder bacteria isolated via Enhanced Quantitative Urinary Culture (EQUC) from healthy postmenopausal women, as well as those with a culture-proven recurrent UTI (rUTI) diagnosis. This repository contains lactobacilli strains from eight different species. As many other lactobacilli are known to inhibit human pathogens, we hypothesized that some urinary lactobacilli will have similar abilities to inhibit the growth of typical uropathogens and thus, provide a link between the urinary microbiome and the predisposition to the rUTI. Therefore, we screened the urinary lactobacilli in our repository for their ability to inhibit model uropathogens in vitro. We observed that many urinary isolates strongly inhibit model strains of gram-negative Escherichia coli and Klebsiella pneumoniae but demonstrate less inhibition of gram-positive Enterococcus faecalis. The observed inhibition affected model strains of uropathogens as well as clinical and multidrug-resistant isolates of those species. Our preliminary analysis of inhibition modes suggests a combination of pH-dependent and cell-dependent inhibition. Overall, inhibition strongly varies among species and strains of urinary lactobacilli. While the strength of the inhibition is not predictive of health outcomes in this limited repository, there is a high level of species and strain diversity that warrants future detailed investigations.

Dietary supplementation of Bacillus velezensis improves Vibrio anguillarum clearance in European sea bass by activating essential innate immune mechanisms

Bacillus spp. supplementation as probiotics in cultured fish diets has a long history of safe and effective use. Specifically, B. velezensis show great promise in fine-tuning the European sea bass disease resistance against the pathogenicity caused by several members of the Vibrio family. However, the immunomodulatory mechanisms behind this response remain poorly understood. Here, to examine the inherent immune variations in sea bass, two equal groups were fed for 30 days with a steady diet, with one treatment supplemented with B. velezensis. The serum bactericidal capacity against live cells of Vibrio anguillarum strain 507 and the nitric oxide and lysozyme lytic activities were assayed. At the cellular level, the phagocytic response of peripheral blood leukocytes against inactivated Candida albicans was determined. Moreover, head-kidney (HK) total leukocytes were isolated from previously in vivo treated fish with LPS of V. anguillarum strain 507. Mechanistically, the expression of some essential proinflammatory genes (interleukin-1 (il1b), tumor necrosis factor-alpha (tnfa), and cyclooxygenase 2 (cox2) and the sea bass specific antimicrobial peptide (AMP) dicentracin (dic) expressions were assessed. Surprisingly, the probiotic supplementation significantly increased all humoral lytic and cellular activities assayed in the treated sea bass. In addition, time-dependent differences were observed between the control and probiotic treated groups for all the HK genes markers subjected to the sublethal LPS dose. Although the il1b was the fastest responding gene to a significant level at 48 h post-injection (hpi), all the other genes followed 72 h in the probiotic supplemented group. Finally, an in vivo bacteria challenge against live V. anguillarum was conducted. The probiotic fed fish observed a significantly higher survival. Overall, our results provide clear vertical evidence on the beneficial immune effects of B. velezensis and unveil some fundamental immune mechanisms behind its application as a probiotic agent in intensively cultured European sea bass.