In vitro antagonistic activity and the protective effect of probiotic Bacillus licheniformis Dahb1 in zebrafish challenged with GFP tagged Vibrio parahaemolyticus Dahv2

Antimicrobial activity of probiotic bacteria-mediated cadmium oxide nanoparticles against fish pathogens

The current research was designed to investigate the antibacterial activity of probiotic bacteria mediated cadmium oxide nanoparticles (CdO NPs) on common fish pathogenic bacteria like Serratia marcescens, Aeromonas hydrophila, Vibrio harveyi, and V. parahaemolyticus. CdO NPs were synthesized using probiotic bacteria as follows: Lactobacillus species with different precursor of cadmium sulfate concentrations (5, 10, and 20 mM). The average crystalline sizes of the CdO NPs were determined based on the XRD patterns using the Debye-Scherrer equation for different precursor concentrations. Specifically, sizes of 40, 48, and 67 nm were found at concentrations of 5, 10, and 20 mM, respectively. The antibacterial efficacy of CdO NPs was estimated using a well diffusion assay, which demonstrated the best efficacy of 20 mM CdO NPs against all pathogens. AFM analysis of nanoparticle-treated and untreated biofilms was performed to further validate the antibacterial effect. Antibacterial activity of CdO nanoparticles synthesized at varying concentrations (5, 10, and 20 mM) against fish pathogens (S. marcescens, A. hydrophila, V. harveyi, and V. parahaemolyticus). The results indicated the highest inhibitory effect of 20 mM CdO NPs across all concentrations (30, 60, and 90 μg/mL), demonstrating significant inhibition against S. marcescens. These findings will contribute to the development of novel strategies for combating aquatic diseases and advancing aquaculture health management practices.

Bacillus licheniformis: A Producer of Antimicrobial Substances, including Antimycobacterials, Which Are Feasible for Medical Applications

Bacillus licheniformis produces several classes of antimicrobial substances, including bacteriocins, which are peptides or proteins with different structural composition and molecular mass: ribosomally synthesized by bacteria (1.4-20 kDa), non-ribosomally synthesized peptides and cyclic lipopeptides (0.8-42 kDa) and exopolysaccharides (>1000 kDa). Different bacteriocins act against Gram-positive or Gram-negative bacteria, fungal pathogens and amoeba cells. The main mechanisms of bacteriocin lytic activity include interaction of peptides with membranes of target cells resulting in structural alterations, pore-forming, and inhibition of cell wall biosynthesis. DNase and RNase activity for some bacteriocines are also postulated. Non-ribosomal peptides are synthesized by special non-ribosomal multimodular peptide synthetases and contain unnatural amino acids or fatty acids. Their harmful effect is due to their ability to form pores in biological membranes, destabilize lipid packaging, and disrupt the peptidoglycan layer. Lipopeptides, as biosurfactants, are able to destroy bacterial biofilms. Secreted polysaccharides are high molecular weight compounds, composed of repeated units of sugar moieties attached to a carrier lipid. Their antagonistic action was revealed in relation to bacteria, viruses, and fungi. Exopolysaccharides also inhibit the formation of biofilms by pathogenic bacteria and prevent their colonization on various surfaces. However, mechanism of the harmful effect for many secreted antibacterial substances remains unknown. The antimicrobial activity for most substances has been studied in vitro only, but some substances have been characterized in vivo and they have found practical applications in medicine and veterinary. The cyclic lipopeptides that have surfactant properties are used in some industries. In this review, special attention is paid to the antimycobacterials produced by B. licheniformis as a possible approach to combat multidrug-resistant and latent tuberculosis. In particular, licheniformins and bacitracins have shown strong antimycobacterial activity. However, the medical application of some antibacterials with promising in vitro antimycobacterial activity has been limited by their toxicity to animals and humans. As such, similar to the enhancement in the antimycobacterial activity of natural bacteriocins achieved using genetic engineering, the reduction in toxicity using the same approach appears feasible. The unique capability of B. licheniformis to synthesize and produce a range of different antibacterial compounds means that this organism can act as a natural universal vehicle for antibiotic substances in the form of probiotic cultures and strains to combat various types of pathogens, including mycobacteria.

Potential application of the probiotic Bacillus licheniformis as an adjuvant in the treatment of diseases in humans and animals: A systematic review

The use of Bacillus licheniformis as a probiotic has increased significantly in recent years. Published reports demonstrate that it provides multiple benefits for health. Although there are already studies in humans and is marketed, it is mostly used in the veterinary industry still. However, its benefits could be extrapolated to humans in future. This review addresses the application of B. licheniformis, its sporulation, mechanisms of action, and its role in the resolution, treatment, and prevention of different conditions and diseases. It focuses on scientific advances from 2016 to mid-2022 and emphasizes the most common diseases in the general population. Most of the 70% of published studies about the health benefits of B. licheniformis have been published from 2016 until now. The intake of B. licheniformis has been related to the effects of modulation of the intestinal microbiota, antimicrobial activity, growth promotion, anti-inflammatory and immunostimulatory effects, promotion of the regulation of the lipid profile, increase of neurotransmitters, and stress reduction, among others. These results provide novel possible applications of this and other probiotics in general. Although many benefits can be reported on a microorganism, the combination with others could provide a better effect. Further studies like this need to be done to understand the specific advantages of each probiotic and its strains and therefore achieve a better selection of them for a specific disease or disorder.

Dietary SYNSEA probiotic improves the growth of white shrimp, Litopenaeus vannamei and reduces the risk of Vibrio infection via improving immunity and intestinal microbiota of shrimp

The growth performance, immunological status, and intestinal microbiology of white shrimp, Litopenaeus vannamei, were evaluated after dietary administration of the commercial probiotic SYNSEA. Shrimp were fed a control diet (without probiotic supplement) and two levels of SYNSEA probiotic, a low concentration of SYNSEA (LSL) containing 10⁵ CFU (g diet)^-1Bacillus subtilis and 10⁵ CFU (g diet)^-1 lactic acid bacteria (LAB), and a high concentration of SYNSEA (LSH) containing 10⁶ CFU (g diet)^-1B. subtilis and 10⁶ CFU (g diet)^-1 LAB, for 12 weeks. Shrimp fed with the LSL diet significantly increased growth performance as well as final weight and feed efficiency compared to the control, but not the LSH diet. After being orally challenged with Vibrio parahaemolyticus, shrimp fed with LSL diet prior to the challenge or fed with LSL and pathogen simultaneously showed significantly lower mortality compared to the control. SYNSEA probiotic significantly improved shrimp immune response, including lysozyme activity in LSL and LSH groups, and phagocytic activity in the LSL group in comparison to the control. In addition, the gene expressions of anti-lipopolysaccharide factor 2 in LSL and LSH groups, and penaeidin 4 in LSL were also up-regulated. Although there was no significant difference among groups for hepatopancreas and intestinal morphology, the muscular layer thickness and villi height were slightly improved in the intestines of shrimp fed SYNSEA. The 16S rDNA gene amplicon sequence analysis using next-generation sequencing revealed a significant decrease in α-diversity (Margalef's species richness) after oral administration of SYNSEA due to an increase in the relative abundance of beneficial bacteria in the gut flora of shrimp, such as Lactobacillus, Shewanella, and Bradymonadales and a decrease in harmful bacteria, such as Vibrio, Candidatus_Berkiella, and Acinetobacter baumannii. Together the data suggest that the provision of SYNSEA probiotic at 10⁵ CFU (g diet)^-1B. subtilis and 10⁵ CFU (g diet)^-1 LAB can improve shrimp growth, enhance immunity, and disease resistance status of the host. In addition, these findings conclude that SYNSEA probiotic has great preventive and therapeutic potential for Vibrio infection in shrimp aquaculture.

Inhibitory effect of probiotic Bacillus spp. isolated from the digestive tract of Rhynchocypris Lagowskii on the adhesion of common pathogenic bacteria in the intestinal model

Diseases of fish caused by pathogenic bacteria are an important constraint on aquaculture production. Antibiotics have been widely used to control infectious diseases, but this has led to the emergence of drug-resistant bacteria and affected human health. In this context, probiotics are used as an alternative to antibiotics for the prevention and control of diseases in aquaculture. The aim of this study was to obtain probiotic candidate strains of Bacillus spp. from the gut of Rhynchocypris Lagowskii. Strains were screened by enzyme-producing ability, antagonism assay and antibiotic susceptibility. The safety of the strains to host fish has also been established. The isolated Bacillus licheniformis (LSG1-1) and Bacillus subtilis (LSG2-1) were characterized and performed well in tolerance experiments. In addition, LSG1-1 and LSG2-1 were detected to have higher self-aggregation ability and surface hydrophobicity. In the in vitro adhesion model, LSG1-1 and LSG2-1 showed good adhesion ability and had obvious adhesion inhibitory effect on three pathogens of Aeromonas. Based on the characteristics observed so far, Bacillus licheniformis LSG1-1 and Bacillus subtilis LSG2-1 could form potential probiotic candidates in the digestive tract of R. lagowskii to help combat diseases in aquaculture.

Updating the Role of Probiotics, Prebiotics, and Synbiotics for Tilapia Aquaculture as Leading Candidates for Food Sustainability: a Review

Tilapia production has significantly increased over the past few years due to the adoption of semi-intensive and intensive aquaculture technologies. However, these farming systems have subjected the fish to stressful conditions that suppress their immunity, hence exposing them to various pathogens. The application of antibiotics and therapeutics to enhance disease resistance, survival, and growth performance in aquaculture has been recently banned due to the emergence of antibiotic-resistant bacteria that pose a serious threat to the environment and consumers of aquatic organisms. Hence, the need for an alternative approach based on sustainable farming practices is warranted. Probiotic, prebiotic, and synbiotic use in tilapia production is considered a viable, safe, and environmentally friendly alternative that enhances growth performance, feed utilization, immunity, disease resistance, and fish survival against pathogens and environmental stress. Their inclusion in fish diets and or rearing water improves the general wellbeing of fish. Hence, this review aims at presenting research findings from the use of probiotics, prebiotics, and synbiotics and their effect on survival, growth, growth performance, gut morphology, microbial abundance, enzyme production, immunity, and disease resistance in tilapia aquaculture, while highlighting several hematological, blood biochemical parameters, and omics techniques that have been used to assess fish health. Furthermore, gaps in existing knowledge are addressed and future research studies have been recommended.

Can only one physiological trait determinate the adverse effect of green fluorescent protein (GFP) incorporation on Vibrio virulence?

Green fluorescent protein (GFP) has been used extensively for in situ animal studies that follow up bacterial infection under epifluorescence microscopy. It is assumed that GFP is acting as a "neutral" protein with no influence on the bacterial physiology. To verify this hypothesis, the virulence of Vibrio splendidus ME9, Vibrio anguillarum NB10, and their respective GFP-tagged strains ME9-GFP and NB10-GFP (transconjugants) was compared in vitro and tested in vivo towards blue mussel (Mytilus edulis) larvae. Results showed that the incorporation of GFP negatively impacted the growth and swimming motility of NB10 in vitro. Correspondingly, the mRNA levels of genes involved in bacterial swimming motility (flaA, flaE, and cheR) were significantly down-regulated in NB10-GFP. As for the strain ME9 on the other hand, GFP incorporation only had a negative effect on swimming motility. However, both the strains NB10-GFP and ME9-GFP showed almost the same virulence as their respective parental strain towards mussel larvae in vivo. Overall, the data presented here demonstrated that incorporation of GFP may cause modifications in cell physiology and highlight the importance of preliminary physiological tests to minimize the negative influence of GFP tagging when it is used to monitor the target localization. The study also supports the idea that the virulence of Vibrio species is determined by complex regulatory networks. Notwithstanding the change of a single physiological trait, especially growth or swimming motility, the GFP-tagged Vibrio strain can thus still be considered usable in studies mainly focusing on the virulence of the strain. KEY POINTS: • The effect of GFP incorporation on physiological trait of Vibrio strains. • The virulence in vibrios could be multifactorial. • The stable virulence of Vibrio strains after GFP incorporation.

Dynamic Immune Response to Vibriosis in Pacific Oyster Crassostrea gigas Larvae during the Infection Process as Supported by Accurate Positioning of GFP-Tagged Vibrio Strains

As the immune system is not fully developed during the larval stage, hatchery culture of bivalve larvae is characterized by frequent mass mortality caused by bacterial pathogens, especially Vibrio spp. However, the knowledge is limited to the pathogenesis of vibriosis in oyster larvae, while the immune response to pathogenic microorganisms in this early life stage is still far from being fully elucidated. In this study, we combined green fluorescent protein (GFP)-tagging, histological and transcriptomic analyses to clarify the pathogenesis of experimental vibriosis and the mechanisms used by the host Pacific oyster Crassostrea gigas larvae to resist infection. The Vibrio strains first colonized the digestive system and rapidly proliferated, while only the transcription level of IκB kinase (IKK) and nuclear factor κB (NF-κB) associated with signaling transduction were up-regulated in oyster at 18 h post challenge (hpc). The mRNA levels for integrin β-1, peroxinectin, and heat shock protein 70 (HSP70), which are associated with phagocytosis, cell adhesion, and cytoprotection, were not upregulated until 30 hpc when the necrosis already happened in the larval digestive system. This suggested that the immunity in the early stages of C. gigas is not strong enough to prevent vibriosis and future research may focus on the strengthening of the gastrointestinal immune ability to defend vibriosis in bivalve larvae.

Evaluation of in vitro and in vivo potential of Bacillus subtilis MBTDCMFRI Ba37 as a candidate probiont in fish health management

Bacillus subtilis MBTDCMFRI Ba37 (B. subtilis Ba37), an antibacterial strain isolated from the tropical estuarine habitats of Cochin, was evaluated for in vitro and in vivo potential, and its application as a candidate probiont in fish health management. B. subtilis Ba37 was characterized using their morphological and biochemical properties. It exhibited exoenzymatic activities, tolerance to various physiological conditions and a wide spectrum of antibacterial activity against aquaculture pathogens such as Vibrio and Aeromonas. In co-culture assay, B. subtilis Ba37 inhibited Vibrio anguillarum O1 (V. anguillarum O1) even with the initial cell count of 10⁴ CFUmL^-1. Cytotoxicity assay performed using the cell free supernatant (CFS) of B. subtilis Ba37 revealed its non toxic nature. A twenty one days of feeding trial was conducted in juveniles of Etroplus suratensis (E.suratensis) by administrating B. subtilis Ba37 to evaluate its efficacy on growth, immune parameters and antioxidant enzyme activities. Overall the supplementation of B. subtilis Ba37 enhanced significantly (P < 0.05) the survival rate, weight gain, specific growth (SGR), feed conversion ratio (FCR), protein efficiency ratio (PER), and feed efficiency (FE) of the fed animals as compared with the control. The immune parameters and antioxidant activities such as total protein, alkaline phosphatase (ALP), superoxide dismutase (SOD) and catalase were also improved significantly (P < 0.05) while serum alanine aminotransferase (SGOT) and serum aspartate aminotransferase (SGPT) activities were decreased slightly than the control. After fifteen days of challenge test, the fish fed with B. subtilis Ba37 showed higher relative percentage survival (RPS) than the control. Thus the study indicated the advantages of B. subtilis Ba37 to be used as a candidate probiont, which could be effectively utilized in managing diseases in aquaculture systems and to improve the health of the host.

Antibacterial and probiotic promotion potential of a new soluble soybean polysaccharide‑iron(III) complex

In this study soluble soybean polysaccharide‑iron(III) (SSPS-Fe(III)) was synthesized to investigate the effects on the growth of Escherichia coli, Staphylococcus aureus and Bacillus licheniformis. Two new detection methods of real-time fluorescence quantitative polymerase chain reaction (qRT-PCR) and microcalorimetry were used to evaluate the effects of different concentrations of SSPS-Fe(III) on the growth of three bacteria. The copy numbers of three bacteria showed that SSPS-Fe(III) had different impacts on the growth of E. coli, S. aureus and B. licheniformis. E. coli growth was inhibited by SSPS-Fe(III) in the higher concentration range and S. aureus growth was inhibited at any concentration, however B. licheniformis growth was promoted. The thermogenic curves for growth metabolism of E. coli and S. aureus presented peak shapes while those of B. licheniformis did platform shapes. As SSPS-Fe(III) concentration increased, the peak heights lowered for E. coli and S. aureus, and the time reaching stationary phase advanced for B. licheniformis. These findings demonstrate that SSPS-Fe(III) has an inhibitory effect on the foodborne pathogens of E. coli and S. aureus, and an enhancement on the probiotics of B. licheniformis.

Mining zebrafish microbiota reveals key community-level resistance against fish pathogen infection

The long-known resistance to pathogens provided by host-associated microbiota fostered the notion that adding protective bacteria could prevent or attenuate infection. However, the identification of endogenous or exogenous bacteria conferring such protection is often hindered by the complexity of host microbial communities. Here, we used zebrafish and the fish pathogen Flavobacterium columnare as a model system to study the determinants of microbiota-associated colonization resistance. We compared infection susceptibility in germ-free, conventional and reconventionalized larvae and showed that a consortium of 10 culturable bacterial species are sufficient to protect zebrafish. Whereas survival to F. columnare infection does not rely on host innate immunity, we used antibiotic dysbiosis to alter zebrafish microbiota composition, leading to the identification of two different protection strategies. We first identified that the bacterium Chryseobacterium massiliae individually protects both larvae and adult zebrafish. We also showed that an assembly of 9 endogenous zebrafish species that do not otherwise protect individually confer a community-level resistance to infection. Our study therefore provides a rational approach to identify key endogenous protecting bacteria and promising candidates to engineer resilient microbial communities. It also shows how direct experimental analysis of colonization resistance in low-complexity in vivo models can reveal unsuspected ecological strategies at play in microbiota-based protection against pathogens.

Commensal Microbiota Regulate Vertebrate Innate Immunity-Insights From the Zebrafish

Microbial communities populate the mucosal surfaces of all animals. Metazoans have co-evolved with these microorganisms, forming symbioses that affect the molecular and cellular underpinnings of animal physiology. These microorganisms, collectively referred to as the microbiota, are found on many distinct body sites (including the skin, nasal cavity, and urogenital tract), however the most densely colonized host tissue is the intestinal tract. Although spatially confined within the intestinal lumen, the microbiota and associated products shape the development and function of the host immune system. Studies comparing gnotobiotic animals devoid of any microbes (germ free) with counterparts colonized with selected microbial communities have demonstrated that commensal microorganisms are required for the proper development and function of the immune system at homeostasis and following infectious challenge or injury. Animal model systems have been essential for defining microbiota-dependent shifts in innate immune cell function and intestinal physiology during infection and disease. In particular, the zebrafish has emerged as a powerful vertebrate model organism with unparalleled capacity for in vivo imaging, a full complement of genetic approaches, and facile methods to experimentally manipulate microbial communities. Here we review key insights afforded by the zebrafish into the impact of microbiota on innate immunity, including evidence that the perception of and response to the microbiota is evolutionarily conserved. We also highlight opportunities to strengthen the zebrafish model system, and to gain new insights into microbiota-innate immune interactions that would be difficult to achieve in mammalian models.

Optimization of Bacillus licheniformis MAL tyrosinase: in vitro anticancer activity for brown and black eumelanin

The influence of tyrosinase in catalyzes/stimulates the eumelanin production was studied. Accordingly, bacterial sp. was isolated and identified as Bacillus licheniformis based on 16S rRNA. It could grow and gave monophenolase and diphenolase productivity in medium contained tyrosin and Cu²⁺ only. The tyrosinase enzymes were optimized by studying different environmental and nutritional factors. The maximum monophenolase and diphenolase productivity were obtained at 60 °C, pH9, Cu²⁺(0.01g), liver extract (1 g/L) and the oxygen level fixed at 20%. Also, the mannose as a carbon source increased the monophenolase production 6.2 times. For the first time, two types of eumelanin were extracted by hydrochloric acid treatment. The black and brown eumelanin weighed (0.1 g/100 mL and 0.7 g/100 mL respectively) and characterized by using FTIR and UV/Vis spectroscopy techniques. Their morphological structure and its elemental composition were characterized by SEM and EDAX respectively. The black melanin showed promising anticancer activity towards HEPG-2 and HCT-116 cell lines with IC₅₀ values (6.15, 5.54 μg) compared to Doxorubicin (4.05, 4.45 μg) respectively.

Xylanase and Fermented Polysaccharide of Hericium caputmedusae Reduce Pathogenic Infection of Broilers by Improving Antioxidant and Anti-Inflammatory Properties

Background

Pathogenic infection in broilers has become an important issue in the development of poultry industry. Xylooligosaccharides released from xylan via xylanase and fermented polysaccharide of Hericium caputmedusae (FPHC) have antimicrobial potential against many pathogens.

Objective

We aimed to explore the effects of xylanase and FPHC on pathogenic infection in the broilers (Gallus gallus domesticus).

Methods

Three hundred and thirty 21-day male broilers were assigned into four groups: control group (CG, basic diet), xylanase group (XG, basic diet + xylanase), FPHC group (HG, basic diet + FPHC), and XHG group (basic diet + xylanase + FPHC). Average daily feed intake (ADFI) and daily gain (ADG) were measured. Microflora from broiler feces was analyzed using 16S rRNA sequencing. Serum tumor necrosis factor- (TNF-) α, interleukin-1β (IL-1β), IL-1 receptor antagonist (IL-1ra), IL-10, total antioxidant capacity (T-AOC), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and malondialdehyde (MDA) contents were detected using kits. The variables were compared using the Student t-test between two groups.

Results

Microbiological investigations showed that 75% of broilers were affected by bacterial pathogens in the CG group, most notably by coagulase-negative staphylococci. Comparatively, 15%, 26%, and 5% of broilers were affected by bacterial pathogens in the XG, HG, and XHG groups, respectively. Xylanase and FPHC treatment increased the ratio of ADG to ADFI and antioxidant capacity by increasing the levels of T-AOC, SOD, and GSH-Px and reducing the levels of MDA (P < 0.05). Xylanase and FPHC treatment improved anti-inflammatory capacity by increasing serum levels of IL-1ra and IL-10 and reducing the levels of IL-1β and TNF-α. On the other hand, the treatment increased probiotic concentration of Bacillus licheniformis, Bacillus subtilis, and Lactobacillus plantarum (P < 0.05), which were also proved in cell culture.

Conclusions

Xylanase and FPHC ameliorate pathogen infection by increasing antioxidant and anti-inflammatory activities of broilers via the increase of probiotics.