A star with stripes: zebrafish as an infection model

Identification of Potential Sepsis Therapeutic Drugs Using a Zebrafish Rapid Screening Approach

In the military, combat wound infections can progress rapidly to life-threatening sepsis. The discovery of effective small-molecule drugs to prevent and/or treat sepsis is a priority. To identify potential sepsis drug candidates, we used an optimized larval zebrafish model of endotoxicity/sepsis to screen commercial libraries of drugs approved by the U.S. Food and Drug Administration (FDA) and other active pharmaceutical ingredients (APIs) known to affect pathways implicated in the initiation and progression of sepsis in humans (i.e., inflammation, mitochondrial dysfunction, coagulation, and apoptosis). We induced endotoxicity in 3- and 5-day post fertilization larval zebrafish (characterized by mortality and tail fin edema (vascular leakage)) by immersion exposure to 60 µg/mL Pseudomonas aeruginosa lipopolysaccharide (LPS) for 24 h, then screened for the rescue potential of 644 selected drugs at 10 µM through simultaneous exposure to LPS. After LPS exposure, we used a neurobehavioral assay (light-dark test) to further evaluate rescue from endotoxicity and to determine possible off-target drug side effects. We identified 29 drugs with > 60% rescue of tail edema and mortality. Three drugs (Ketanserin, Tegaserod, and Brexpiprazole) produced 100% rescue and did not differ from the controls in the light-dark test, suggesting a lack of off-target neurobehavioral effects. Further testing of these three drugs at a nearly 100% lethal concentration of Klebsiella pneumoniae LPS (45 µg/mL) showed 100% rescue from mortality and 88-100% mitigation against tail edema. The success of the three identified drugs in a zebrafish endotoxicity/sepsis model warrants further evaluation in mammalian sepsis models.

Current methodologies available to evaluate the virulence potential among Listeria monocytogenes clonal complexes

Listeria monocytogenes is a foodborne pathogen that causes listeriosis in humans, the severity of which depends on multiple factors, including intrinsic characteristics of the affected individuals and the pathogen itself. Additionally, emerging evidence suggests that epigenetic modifications may also modulate host susceptibility to infection. Therefore, different clinical outcomes can be expected, ranging from self-limiting gastroenteritis to severe central nervous system and maternal-neonatal infections, and bacteremia. Furthermore, L. monocytogenes is a genetically and phenotypically diverse species, resulting in a large variation in virulence potential between strains. Multilocus sequence typing (MLST) has been widely used to categorize the clonal structure of bacterial species and to define clonal complexes (CCs) of genetically related isolates. The combination of MLST and epidemiological data allows to distinguish hypervirulent CCs, which are notably more prevalent in clinical cases and typically associated with severe forms of the disease. Conversely, other CCs, termed hypovirulent, are predominantly isolated from food and food processing environments and are associated with the occurrence of listeriosis in immunosuppressed individuals. Reports of genetic traits associated with this diversity have been described. The Food and Agriculture Organization (FAO) is encouraging the search for virulence biomarkers to rapidly identify the main strains of concern to reduce food waste and economical losses. The aim of this review is to comprehensively collect, describe and discuss the methodologies used to discriminate the virulence potential of L. monocytogenes CCs. From the exploration of in vitro and in vivo models to the study of expression of virulence genes, each approach is critically explored to better understand its applicability and efficiency in distinguishing the virulence potential of the pathogen.

Age- and dose-dependent susceptibility of axolotls (Ambystoma mexicanum) by bath exposure to Ambystoma tigrinum virus (ATV)

Ranaviruses are large, dsDNA viruses that have significant ecological and economic impact on cold-blooded vertebrates. However, our understanding of the viral proteins and subsequent host immune response(s) that impact susceptibility to infection and disease is not clear. The ranavirus Ambystoma tigrinum virus (ATV), originally isolated from the Sonoran tiger salamander (Ambystoma mavortium stebbinsi), is highly pathogenic at low doses of ATV at all tiger salamander life stages and this model has been used to explore the host-pathogen interactions of ATV infection. However, inconsistencies in the availability of laboratory reared larval tiger salamanders required us to look at the well characterized axolotl (A. mexicanum) as a model for ATV infection. Data obtained from five infection experiments over different developmental timepoints suggest that axolotls are susceptible to ATV in an age- and dose-dependent manner. These data support the use of the ATV-axolotl model to further explore the host-pathogen interactions of ranavirus infections.

High-Quality Indigo Naturalis Obtained with Automatic Foam Separation

Indigo Naturalis is not only an ancient plant dye but also a famous herbal medicine with antibacterial, anti-inflammatory, and anticancer properties. In traditional processes, thousands of manual stirring separate the high-quality Indigo Naturalis from the crude pulp system. However, this method is time-consuming and labor-intensive, resulting in an unstable quality and low yield, which cannot meet the requirements of modern industrial production. In this study, foam-separation technology was used to increase the industrial applicability of high-quality Indigo Naturalis. The process parameters were optimized based on the content of active ingredients, skin irritation effects, and antioxidative stress activity. The results showed that the optimal process of the foam separation achieved the liquid level difference of 40 cm and the foaming intensity of 0.35 MPa. Compared with the original sample, the indigo and indirubin contents in purified Indigo Naturalis were 1.6 and 3 times higher, the total ash content decreased from 86 to 70%, the pH value decreased from 12.18 to 9.71, and the leachate doubled. Animal experiments suggested the significantly reduced irritation (p < 0.01) and enhanced antioxidative stress activity (p < 0.01) of Indigo Naturalis after foam separation. Therefore, the foam-separation equipment developed in this study enabled the refinement of active ingredients in Indigo Naturalis, which greatly improved the production efficiency and quality.

Antibacterial activity of the novel compound Sudapyridine (WX-081) against Mycobacterium abscessus

Objective

This study aimed to investigate sudapyridine (WX-081) antibacterial activity against Mycobacterium abscessus in vitro and its effect on in vivo bacterial growth and host survival using a zebrafish model of M. abscessus infection.

Methods

WX-081 in vitro antibacterial activity was assessed based on growth inhibition of M. abscessus standard strain ATCC19977 and 36 clinical isolates. Maximum tolerated concentrations (MTCs) of WX-081, bedaquiline, and azithromycin and inhibition of M. abscessus growth were assessed in vivo after fluorescently labelled bacilli and drugs were injected into zebrafish. Bacterial counts were analysed using one-way ANOVA and fluorescence intensities of zebrafish tissues were analysed and expressed as the mean ± SE. Moreover, Kaplan-Meier survival analysis was conducted to assess intergroup differences in survival of M. abscessus-infected zebrafish treated with different drug concentrations using a log-rank test, with a p value <0.05 indicating a difference was statistically significant.

Results

Drug sensitivity testing of M. abscessus standard strain ATCC19977 and 36 clinical isolates revealed MICs ranging from 0.12-0.96 µg/mL and MIC50 and MIC90 values of 0.48 µg/mL and 0.96 µg/mL, respectively. Fluorescence intensities of M. abscessus-infected zebrafish tissues was lower after treatment with the WX-081 MTC (62.5 µg/mL) than after treatment with the azithromycin MTC (62.5 µg/mL) and the bedaquiline MTC (15.6 µg/mL). When the concentration of WX-081 increased from 1.95µg/mL to 1/8 MTC(7.81µg/mL), the survival rate of zebrafish at 4-9 dpf decreased from 90.00% to 81.67%.

Conclusion

WX-081 effectively inhibited M. abscessus growth in vitro and in vivo and prolonged survival of M. abscessus-infected zebrafish, thus indicating that WX-081 holds promise as a clinical treatment for M. abscessus infection.

Antibacterial activity of the novel oxazolidinone contezolid (MRX-I) against Mycobacterium abscessus

Objective

To evaluate contezolid (MRX-I) antibacterial activity against Mycobacterium abscessus in vitro and in vivo and to assess whether MRX-I treatment can prolong survival of infected zebrafish.

Methods

MRX-I inhibitory activity against M. abscessus in vitro was assessed by injecting MRX-I into zebrafish infected with green fluorescent protein-labelled M. abscessus. Thereafter, infected zebrafish were treated with azithromycin (AZM), linezolid (LZD) or MRX-I then maximum tolerated concentrations (MTCs) of drugs were determined based on M. abscessus growth inhibition using one-way ANOVA. Linear trend analysis of CFU counts and fluorescence intensities (mean ± SE values) was performed to detect linear relationships between MRX-I, AZM and LZD concentrations and these parameters.

Results

MRX-I anti-M. abscessus minimum inhibitory concentration (MIC) and MTC were 16 μg/mL and 15.6 μg/mL, respectively. MRX-I MTC-treated zebrafish fluorescence intensities were significantly lower than respective LZD group intensities (whole-body: 439040 ± 3647 vs. 509184 ± 23064, p < 0.01); head: 74147 ± 2175 vs. 95996 ± 8054, p < 0.05). As MRX-I concentration was increased from 0.488 μg/mL to 15.6 μg/mL, zebrafish whole-body, head and heart fluorescence intensities decreased. Statistically insignificant differences between the MRX-I MTC group survival rate (78.33%) vs. corresponding rates of the 62.5 μg/mL-treated AZM MTC group (88.33%, p > 0.05) and the 15.6 μg/mL-treated LZD MTC group (76.67%, p > 0.05) were observed.

Conclusion

MRX-I effectively inhibited M. abscessus growth and prolonged zebrafish survival when administered to M. abscessus-infected zebrafish, thus demonstrating that MRX-I holds promise as a clinical treatment for human M. abscessus infections.

CD271 activation prevents low to high-risk progression of cutaneous squamous cell carcinoma and improves therapy outcomes

BACKGROUND

Cutaneous squamous cell carcinoma (cSCC) is the second most prevalent form of skin cancer, showing a rapid increasing incidence worldwide. Although most cSCC can be cured by surgery, a sizeable number of cases are diagnosed at advanced stages, with local invasion and distant metastatic lesions. In the skin, neurotrophins (NTs) and their receptors (CD271 and Trk) form a complex network regulating epidermal homeostasis. Recently, several works suggested a significant implication of NT receptors in cancer. However, CD271 functions in epithelial tumors are controversial and its precise role in cSCC is still to be defined.

METHODS

Spheroids from cSCC patients with low-risk (In situ or Well-Differentiated cSCC) or high-risk tumors (Moderately/Poorly Differentiated cSCC), were established to explore histological features, proliferation, invasion abilities, and molecular pathways modulated in response to CD271 overexpression or activation in vitro. The effect of CD271 activities on the response to therapeutics was also investigated. The impact on the metastatic process and inflammation was explored in vivo and in vitro, by using zebrafish xenograft and 2D/3D models.

RESULTS

Our data proved that CD271 is upregulated in Well-Differentiated tumors as compared to the more aggressive Moderately/Poorly Differentiated cSCC, both in vivo and in vitro. We demonstrated that CD271 activities reduce proliferation and malignancy marker expression in patient-derived cSCC spheroids at each tumor grade, by increasing neoplastic cell differentiation. CD271 overexpression significantly increases cSCC spheroid mass density, while it reduces their weight and diameter, and promotes a major fold-enrichment in differentiation and keratinization genes. Moreover, both CD271 overexpression and activation decrease cSCC cell invasiveness in vitro. A significant inhibition of the metastatic process by CD271 was observed in a newly established zebrafish cSCC model. We found that the recruitment of leucocytes by CD271-overexpressing cells directly correlates with tumor killing and this finding was further highlighted by monocyte infiltration in a THP-1-SCC13 3D model. Finally, CD271 activity synergizes with Trk receptor inhibition, by reducing spheroid viability, and significantly improves the outcome of photodynamic therapy (PTD) or chemotherapy in spheroids and zebrafish.

CONCLUSION

Our study provides evidence that CD271 could prevent the switch between low to high-risk cSCC tumors. Because CD271 contributes to maintaining active differentiative paths and favors the response to therapies, it might be a promising target for future pharmaceutical development.

Luteolin, a promising quorum quencher mitigates virulence factors production in Pseudomonas aeruginosa - In vitro and In vivoapproach

Pseudomonas aeruginosa (PA) is an opportunistic pathogen that causes healthcare-associated infection and high mortality in immunocompromised patients. It produces several virulence factors through quorum sensing (QS) mechanisms that is essential for subverting host immune system. Even front-line antibiotics are unable to control PA pathogenicity due to the emergence of antibiotic resistance. Luteolin is a naturally derived compound that has proven to be the effective drug to annihilate pathogens through quorum quenching mechanism. In this study, the protective effect of luteolin against the PA-mediated inflammation was demonstrated using zebrafish model. Luteolin protects zebrafish from PA infection and increases their survival rate. It was found that PA-mediated ROS, lipid peroxidation, and apoptosis were also significantly reduced in luteolin-treated zebrafish larvae. Open field test (OFT) reveals that luteolin rescued PA-infected zebrafish from retarded swimming behavior. Furthermore, luteolin increases SOD and CAT levels and decreases LDH and NO levels in PA-infected zebrafish compare to control group. Histological and gene expression analysis reveals that luteolin protects PA-infected zebrafish by decreasing gut inflammation and altering the expression of inflammatory (TNF-α, IL-1β, IL-6) and antioxidant markers (iNOS, SOD, CAT). Thus, luteolin was found to have dual effect in protecting PA-infected zebrafish by decreasing virulence factors production in PA and stimulating host immune system. This is the first study demonstrating the protective effect of luteolin using animal model. Hence, luteolin could be used as a future therapeutic drug to control multi-drug resistant PA.

Evaluation of extraction methods for untargeted metabolomic studies for future applications in zebrafish larvae infection models

Sample preparation in untargeted metabolomics should allow reproducible extractions of as many molecules as possible. Thus, optimizing sample preparation is crucial. This study compared six different extraction procedures to find the most suitable for extracting zebrafish larvae in the context of an infection model. Two one-phase extractions employing methanol (I) and a single miscible phase of methanol/acetonitrile/water (II) and two two-phase methods using phase separation between chloroform and methanol/water combinations (III and IV) were tested. Additional bead homogenization was used for methods III and IV (III_B and IV_B). Nine internal standards and 59 molecules of interest (MoInt) related to mycobacterial infection were used for method evaluation. Two-phase methods (III and IV) led to a lower feature count, higher peak areas of MoInt, especially amino acids, and higher coefficients of variation in comparison to one-phase extractions. Adding bead homogenization increased feature count, peak areas, and CVs. Extraction I showed higher peak areas and lower CVs than extraction II, thus being the most suited one-phase method. Extraction III and IV showed similar results, with III being easier to execute and less prone to imprecisions. Thus, for future applications in zebrafish larvae metabolomics and infection models, extractions I and III might be chosen.

Bombyx mori as a model for Niallia circulans pathogenicity

Increasing incidences of resistance to antibiotics by pathogenic bacteria is a worldwide concern and isolation of antibiotic-resistant strains of Niallia circulans (formerly known as Bacillus circulans), an opportunistic human pathogen, has been reported. Due to their lack of ethical constraints as well as their cost-effective rearing, invertebrates have been commonly used to study infection by bacteria pathogenic to humans. In this study, we demonstrate that a foodborne strain of N. circulans kills larvae of the silkworm, Bombyx mori within 48 h after hemolymph injection. The infected larvae turned black with an increase in the phenoloxidase (PO) activity in the hemolymph. Midgut injection of N. circulans resulted in the killing of larvae within 96 h. A significant increase in bacterial load was observed in the hemolymph 12 h after infection. The viable hemocyte number decreased to 48% within 12 h of injection. RT-qPCR analysis revealed that upon hemolymph infection with N. circulans the expression of the antimicrobial peptide (AMP) genes, Bmdefensin-B and Bmgloverin-3, were upregulated 2.5- and 1.8-fold, respectively, whereas 1.6-fold upregulation was observed for BmToll-2 in the larval fat body. Therapeutic effects of antibiotics like tetracycline, imipenem, ceftriaxone, ampicillin, and clindamycin were observed against N. circulans in the Bombyx larvae with varying efficacies. Results from this study suggest that larvae of B. mori can be used as infection models for screening therapeutics that are effective against N. circulans.

Shewanella spp. from wastewater treatment plant-affected environment: isolation and characterization

Bacteria from the genus Shewanella are inhabitants of marine and freshwater ecosystems, recognized fish spoilage bacteria, but less known as fish disease agents. Shewanella spp. isolated from fish living in waters close to effluents of a wastewater treatment plant (WWTP) were not previously characterized. We have tested Shewanella isolates from WWTP-affected waters and related fish. Genotypic characterization identified most strains as S. baltica and S. oneidensis. In order to investigate the sensibility and accuracy of their MALDI-TOF MS identification, they were grown on two culture media enriched by various NaCl concentrations, incubated at different temperatures and duration. We analyzed their antimicrobial susceptibility on a panel of antimicrobial drugs and capacity for biofilm production. With a view to demonstrate their capacity to produce fatty acids, we assessed the impact of different culture media on their lipid profile. We performed zebrafish embryotoxicity tests to simulate the environmental infection of the earliest life stages in S. baltica-contaminated waters. The best MALDI-TOF MS identification scores were for strains cultivated on TSA for 24 h at 22 °C and with supplementation of 1.5% NaCl. Less than 17% of isolates demonstrated antimicrobial resistance. Most isolates were weak biofilm producers. Strain-to-strain variation of MIC and MBC was low. The major fatty acids were C15:0, C16:0, C16:1, C17:1, and iC15:0. Exposure of Danio rerio to different S. baltica concentrations induced severe effects on zebrafish development: decreased heartbeat rate, locomotor activity, and melanin pigmentation. S. baltica passed through chorionic pores of zebrafish.

Meningococcal virulence in zebrafish embryos depends on capsule polysaccharide structure

Neisseria meningitidis or the meningococcus, can cause devasting diseases such as sepsis and meningitis. Its polysaccharide capsule, on which serogrouping is based, is the most important virulence factor. Non-encapsulated meningococci only rarely cause disease, due to their sensitivity to the host complement system. How the capsular polysaccharide structure of N. meningitidis relates to virulence is largely unknown. Meningococcal virulence can be modeled in zebrafish embryos as the innate immune system of the zebrafish embryo resembles that of mammals and is fully functional two days post-fertilization. In contrast, the adaptive immune system does not develop before 4 weeks post-fertilization. We generated isogenic meningococcal serogroup variants to study how the chemical composition of the polysaccharide capsule affects N. meningitidis virulence in the zebrafish embryo model. H44/76 serogroup B killed zebrafish embryos in a dose-dependent manner, whereas the non-encapsulated variant was completely avirulent. Neutrophil depletion was observed after infection with encapsulated H44/76, but not with its non-encapsulated variant HB-1. The survival of embryos infected with isogenic capsule variants of H44/76 was capsule specific. The amount of neutrophil depletion differed accordingly. Both embryo killing capacity and neutrophil depletion after infection correlated with the number of carbons used per repeat unit of the capsule polysaccharide during its biosynthesis (indicative of metabolic cost).

Conclusion

Meningococcal virulence in the zebrafish embryo largely depends on the presence of the polysaccharide capsule but the extent of the contribution is determined by its structure. The observed differences between the meningococcal isogenic capsule variants in zebrafish embryo virulence may depend on differences in metabolic cost.

Expression and biological activity of lytic proteins HolST-3 and LysST-3 of Salmonella phage ST-3

Salmonella infection is a major public health concern. Several strategies for Salmonella infection prevention and control are currently available including vaccines and antibiotics. However, vaccines are expensive and inefficient, and the use of antibiotics can lead to antibiotic resistance. Thus, alternative strategies for the treatment of Salmonella remain warrant. In this study, recombinant holin HolST-3 and lysin LysST-3 from Salmonella phage ST-3 were expressed and purified, and their bactericidal properties were analyzed. HolST-3 and LysST-3 possessed a wider lysis spectrum and more efficient bactericidal effect than phage ST-3, and a synergistic bactericidal effect was observed when combined in vitro. In addition, we explored the bactericidal properties of HolST-3 and LysST-3 in vivo using zebrafish as a model organism, and found that the bactericidal effects of both HolST-3 and LysST-3 in vivo were comparable to those of cefotaxime, an antibiotic. This study provides a basis for the development of HolST-3 and LysST-3 as novel bactericidal agents for the prevention and treatment of infectious diseases caused by Salmonella spp.

Mycobacteriophage-antibiotic therapy promotes enhanced clearance of drug-resistant Mycobacterium abscessus

Infection by multidrug-resistant Mycobacterium abscessus is increasingly prevalent in cystic fibrosis (CF) patients, leaving clinicians with few therapeutic options. A compassionate study showed the clinical improvement of a CF patient with a disseminated M. abscessus (GD01) infection, following injection of a phage cocktail, including phage Muddy. Broadening the use of phage therapy in patients as a potential antibacterial alternative necessitates the development of biological models to improve the reliability and successful prediction of phage therapy in the clinic. Herein, we demonstrate that Muddy very efficiently lyses GD01 in vitro, an effect substantially increased with standard drugs. Remarkably, this cooperative activity was retained in an M. abscessus model of infection in CFTR-depleted zebrafish, associated with a striking increase in larval survival and reduction in pathological signs. The activity of Muddy was lost in macrophage-ablated larvae, suggesting that successful phage therapy relies on functional innate immunity. CFTR-depleted zebrafish represent a practical model to rapidly assess phage treatment efficacy against M. abscessus isolates, allowing the identification of drug combinations accompanying phage therapy and treatment prediction in patients.

This article has an associated First Person interview with the first author of the paper.

Summary: A zebrafish model of infection was developed to evaluate the in vivo cooperative activity of specific phages and antibiotics for the treatment of Mycobacterium abscessus infection.

Role of germ-free animal models in understanding interactions of gut microbiota to host and environmental health: A special reference to zebrafish

Numerous pieces of evidence documented the importance of gut microbiota in regulating human health and evaluating the toxicity of environmental pollutants, which are closely related to the host health in various aspects, including nutrition, energy translation, metabolism, pathogen resistance, and immune function. A variety of environmental factors can disrupt gut microbiota and their functions, and inevitably cause immune diseases, obesity and diabetes. However, deciphering the inner mechanisms involved in the functional interaction of gut microbes with host health is still needed extensive investigations. This review focused on the essential roles of intestinal microbes in host-related diseases and highlighted the development and applications of germ-free (GF) animal models, mainly zebrafish. Moreover, the generation, immunity characters, advantages and challenges of GF zebrafish models were also summarized. Importantly, the composition and isolation of zebrafish gut bacteria for further application and toxicity evaluation of aquatic environmental pollutants were also discussed. In conclusion, GF zebrafish play irreplaceable roles in understanding the potential functions and responses of customized microbiota towards human and environmental health implications.

An overview of Acinetobacter baumannii pathogenesis: Motility, adherence and biofilm formation

The Gram-negative opportunistic pathogen Acinetobacter baumannii has gain notoriety in recent decades, primarily due to its propensity to cause nosocomial infections in critically ill patients. Its global spread, multi-drug resistance features and plethora of virulence factors make it a serious threat to public health worldwide. Though much effort has been expended in uncovering its successes, it continues to confound researchers due to its highly adaptive nature, mutating to meet the needs of a given environment. Its persistence in the clinical setting allows it to be in close proximity to a potential host, where contact can be made facilitating infection and colonization. In this article, we aim to provide a current overview of the bacterial virulence factors, specifically focusing on factors involved in the initial stages of infection, highlighting the role of adaptation facilitated by two-component systems and biofilm formation. Finally, the study of host-pathogen interactions using available animal models, their suitability, notable findings and some perspectives moving forward are also discussed.

Synthesis and characterization of hesperetin derivatives and toxicity level of the zebrafish model

Hesperetin derivatives were synthesized through the esterification of acid chlorides with hesperetin under ambient reaction conditions with good yields. The product was confirmed using different spectral techniques. It was treated on zebrafish embryos to study the lethality, phenotypic deformities, and toxicity level of the compound. In that assessment, embryos showed lethality towards 3e at the minimal concentration. It assesses slow heartbeat since the compound loaded, the curvature on the back, upcurved fish, Cardiac chamber bulging, and poor survival rate in 72 h. 3a shows less toxicity more than other compounds. It shows only pericardial edema at higher concentration and 3c induced pericardial edema and upcurved tail at a medium range of the concentration. But both compounds were shown a good survival ratio at the minimal concentration.

CFTR Depletion Confers Hypersusceptibility to Mycobacterium fortuitum in a Zebrafish Model

The Mycobacterium fortuitum complex comprises several closely related species, causing pulmonary and extra-pulmonary infections. However, there is very limited knowledge about the disease pathogenesis involved in M. fortuitum infections, particularly due to the lack of suitable animal models. Using the zebrafish model, we show that embryos are susceptible to M. fortuitum infection in a dose-dependent manner. Furthermore, zebrafish embryos form granulomas from as early as 2 days post-infection, recapitulating critical aspects of mycobacterial pathogenesis observed in other pathogenic species. The formation of extracellular cords in infected embryos highlights a previously unknown pathogenic feature of M. fortuitum. The formation of large corded structures occurs also during in vitro growth, suggesting that this is not a host-adapted stress mechanism deployed during infection. Moreover, transient macrophage depletion led to rapid embryo death with increased extracellular cords, indicating that macrophages are essential determinants of M. fortuitum infection control. Importantly, morpholino depletion of the cystic fibrosis transmembrane conductance regulator (cftr) significantly increased embryo death, bacterial burden, bacterial cords and abscesses. There was a noticeable decrease in the number of cftr-deficient infected embryos with granulomas as compared to infected controls, suggesting that loss of CFTR leads to impaired host immune responses and confers hypersusceptiblity to M. fortuitum infection. Overall, these findings highlight the application of the zebrafish embryo to study M. fortuitum and emphasizes previously unexplored aspects of disease pathogenesis of this significant mycobacterial species.

Zebrafish embryo sensitivity test as in vivo platform to anti-Shiga toxin compound screening

Shiga toxin-producing Escherichia coli (STEC) pathotype secretes two types of AB₅ cytotoxins (Stx1 and Stx2), responsible for complications such as hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS) in infected patients, which could lead to sequels and death. Currently, there is no effective treatment against the cytotoxic effect of these toxins. However, in order to approve any therapy molecule, an animal experiment is required in order to evaluate the efficacy and safety of therapeutic approaches. The use of alternative small host models is growing among human infectious disease studies, particularly the vertebrate zebrafish model, since relevant results have been described for pathogen-host interaction. In this sense, the present work aimed to analyze the toxic effect of Shiga toxins in zebrafish embryo model in order to standardize this method in the future to be used as a fast, simple, and efficient methodology for the screening of therapeutic molecules. Herein, we demonstrated that the embryos were sensitive in a dose-dependent manner to both Stx toxins, with LD₅₀ of 22 μg/mL for Stx1 and 33 μg/mL for Stx2, and the use of anti-Stx polyclonal antibody abolished the toxic effect. Therefore, this methodology can be a rapid alternative method for selecting promising compounds against Stx toxins, such as recombinant antibodies.

Therapeutic Effect of Antibiotics Against Escherichia coli O157:H7 in Silk Moth Larvae Animal Model

The increasing clinical incidence of antibiotic resistance in bacteria is a major global health care issue. Rampant use of antimicrobials is one of the major reasons of the dramatic rise in antibiotic-resistant bacterial strains. Suitable animal models are required to improve our understanding of bacterial pathogenicity, evolution and search for novel antibiotics. The larvae of the silk moth (commonly called silkworm), Bombyx mori, have been used as an animal model for testing the pathogenicity of a clinically isolated strain of enterohemorrhagic Escherichia coli O157:H7 upon injection through hemolymph. Here, we show that a foodborne E. coli O157:H7 strain can kill silkworm larvae upon injection through either hemolymph (blood) or midgut. Bacterial number in the hemolymph started to increase after 3 h of injection into hemolymph, while the number of viable circulating hemocytes decreased. Administration of four well-known antibiotics into the larval hemolymph up to 100 µg per larva showed therapeutic effect with varying efficacies against E. coli O157:H7 with ceftriaxone and imipenem showing better effect. Our findings indicate that silkworm larvae can be used as an animal model to screen for novel antibiotics that are effective against E. coli O157:H7.

Determining macrophage versus neutrophil contributions to innate immunity using larval zebrafish

The specific roles of the two major innate immune cell types – neutrophils and macrophages – in response to infection and sterile inflammation are areas of great interest. The larval zebrafish model of innate immunity, and the imaging capabilities it provides, is a source of new research and discoveries in this field. Multiple methods have been developed in larval zebrafish to specifically deplete functional macrophages or neutrophils. Each of these has pros and cons, as well as caveats, that often make it difficult to directly compare results from different studies. The purpose of this Review is to (1) explore the pros, cons and caveats of each of these immune cell-depleted models; (2) highlight and place into a broader context recent key findings on the specific functions of innate immune cells using these models; and (3) explore future directions in which immune cell depletion methods are being expanded.

Summary: Macrophages and neutrophils are distinct innate immune cells with diverse roles in diverse inflammatory contexts. Recent research in larval zebrafish using cell-specific depletion methods has revealed new insights into these cells' functions.

Macrophages in Zebrafish Models of Liver Diseases

Hepatic macrophages are key components of the liver immunity and consist of two main populations. Liver resident macrophages, known as Kupffer cells in mammals, are crucial for maintaining normal liver homeostasis. Upon injury, they become activated to release proinflammatory cytokines and chemokines and recruit a large population of inflammatory monocyte-derived macrophages to the liver. During the progression of liver diseases, macrophages are highly plastic and have opposing functions depending on the signaling cues that they receive from the microenvironment. A comprehensive understanding of liver macrophages is essential for developing therapeutic interventions that target these cells in acute and chronic liver diseases. Mouse studies have provided the bulk of our current knowledge of liver macrophages. The emergence of various liver disease models and availability of transgenic tools to visualize and manipulate macrophages have made the teleost zebrafish (Danio rerio) an attractive new vertebrate model to study liver macrophages. In this review, we summarize the origin and behaviors of macrophages in healthy and injured livers in zebrafish. We highlight the roles of macrophages in zebrafish models of alcoholic and non-alcoholic liver diseases, hepatocellular carcinoma, and liver regeneration, and how they compare with the roles that have been described in mammals. We also discuss the advantages and challenges of using zebrafish to study liver macrophages.

Zebrafish as a preclinical in vivo screening model for nanomedicines

The interactions of nanomedicines with biological environments is heavily influenced by their physicochemical properties. Formulation design and optimization are therefore key steps towards successful nanomedicine development. Unfortunately, detailed assessment of nanomedicine formulations, at a macromolecular level, in rodents is severely limited by the restricted imaging possibilities within these animals. Moreover, rodent in vivo studies are time consuming and expensive, limiting the number of formulations that can be practically assessed in any one study. Consequently, screening and optimisation of nanomedicine formulations is most commonly performed in surrogate biological model systems, such as human-derived cell cultures. However, despite the time and cost advantages of classical in vitro models, these artificial systems fail to reflect and mimic the complex biological situation a nanomedicine will encounter in vivo. This has acutely hampered the selection of potentially successful nanomedicines for subsequent rodent in vivo studies. Recently, zebrafish have emerged as a promising in vivo model, within nanomedicine development pipelines, by offering opportunities to quickly screen nanomedicines under in vivo conditions and in a cost-effective manner so as to bridge the current gap between in vitro and rodent studies. In this review, we outline several advantageous features of the zebrafish model, such as biological conservation, imaging modalities, availability of genetic tools and disease models, as well as their various applications in nanomedicine development. Critical experimental parameters are discussed and the most beneficial applications of the zebrafish model, in the context of nanomedicine development, are highlighted.

Transcriptomic characterization of adult zebrafish infected with Streptococcus agalactiae

Streptococcus agalactiae is a major aquaculture pathogen infecting various saltwater and freshwater fish. To better understand the mechanism of the immune responses to S. agalactiae in wildtype zebrafish, the transcriptomic profiles of two organs containing mucosal-associated lymphoid tissues from S. agalactiae-infected and non-infected groups were obtained using RNA-seq techniques. In the intestines, 6735 and 12908 differently expressed genes (DEGs) were identified at 24 hpi and 48 hpi, respectively. Among 66 and 116 significantly enriched pathways, 15 and 21 pathways were involved in immune system or signal transduction at 24 hpi and 48 hpi, respectively. A number of genes involved in Toll-like receptor signaling pathway, RIG-I-like receptor signaling pathway, NOD-like receptor signaling pathway, T cell receptor signaling pathway, B cell receptor signaling pathway, Antigen processing and presentation, NF-kappa B signaling pathway and PI3K-Akt signaling pathway were significantly downregulated. In the skins, 3113 and 4467 DEGs were identified at 24 hpi and 48 hpi, respectively. Among 24 and 56 significantly enriched pathways, 4 and 13 pathways were involved in immune system or signal transduction at 24 hpi and 48 hpi, respectively. More immune-related signaling pathways including Leukocyte transendothelial migration, Cytokine-cytokine receptor interaction, PI3K-Akt signaling pathway, IL-17 signaling pathway, MAPK signaling pathway, TNF signaling pathway, Complement and coagulation cascades, Hematopoietic cell lineage and Jak-STAT signaling pathway were differently enriched for upregulated DEGs at 48 hpi, which were completely different from that in the intestines. Furthmore, comparative transcriptome analysis revealed that the downregulated 1618 genes and upregulated 1622 genes existed both at 24 hpi and 48 hpi for the intestine samples. In the skins, the downregulated 672 genes and upregulated 428 genes existed both at 24 hpi and 48 hpi. Three pathways related to immune processes were significantly enriched for downregulated DEGs both in the intestines and skins collected at 24 hpi and 48 hpi, which included Antigen processing and presentation, Intestinal immune network for IgA production and Hematopoietic cell lineage. Interaction network analysis of DEGs identified the main DEGs in the sub-network of complement and coagulation cascades both in the intestines and skins. Twenty of DEGs involved in complement and coagulation cascades were further validated by Real-time quantitative PCR. Altogether, the results obtained in this study will provide insight into the immune response of zebrafish against S. agalactiae XQ-1 infection in fatal conditions, and reveal the discrepant expression pattern of complement and coagulation cascades in the intestines and skins.

Alternative Experimental Models for Studying Influenza Proteins, Host-Virus Interactions and Anti-Influenza Drugs

Ninety years after the discovery of the virus causing the influenza disease, this malady remains one of the biggest public health threats to mankind. Currently available drugs and vaccines only partially reduce deaths and hospitalizations. Some of the reasons for this disturbing situation stem from the sophistication of the viral machinery, but another reason is the lack of a complete understanding of the molecular and physiological basis of viral infections and host-pathogen interactions. Even the functions of the influenza proteins, their mechanisms of action and interaction with host proteins have not been fully revealed. These questions have traditionally been studied in mammalian animal models, mainly ferrets and mice (as well as pigs and non-human primates) and in cell lines. Although obviously relevant as models to humans, these experimental systems are very complex and are not conveniently accessible to various genetic, molecular and biochemical approaches. The fact that influenza remains an unsolved problem, in combination with the limitations of the conventional experimental models, motivated increasing attempts to use the power of other models, such as low eukaryotes, including invertebrate, and primary cell cultures. In this review, we summarized the efforts to study influenza in yeast, Drosophila, zebrafish and primary human tissue cultures and the major contributions these studies have made toward a better understanding of the disease. We feel that these models are still under-utilized and we highlight the unique potential each model has for better comprehending virus-host interactions and viral protein function.

Notch1a can widely mediate innate immune responses in zebrafish larvae infected with Vibrio parahaemolyticus

The Notch signaling pathway is known to regulate innate immunity by influencing macrophage function and interacting with the Toll-like receptor (TLR) signaling pathway. However, the comprehensive role of the Notch signaling pathway in the innate immune response remains unknown. To assess the function of Notch1a in immunity, we examined the innate immune responses to Vibrio parahaemolyticus strain Vp13 of wild-type (WT) and notch1a^-/- zebrafish larvae generated using the clustered regularly interspaced short palindromic repeats/CRISPR associated protein 9 (CRISPR/Cas9) system. The median lethal dose (LD₅₀) of V. parahaemolyticus was significantly lower in notch1a^-/- larvae than in WT larvae 3 days post fertilization (dpf). Transcriptome data analysis revealed 359 significantly differentially expressed genes (DEGs), including 246 significantly down-regulated genes and 113 significantly up-regulated genes, in WT infected groups compared with WT control groups. In contrast, 986 significantly DEGs were found in notch1a^-/- infected groups compared with notch1a^-/- control groups, of which 82 genes were significantly down-regulated and 904 genes were significantly up-regulated. These DEGs belonged to the tumor necrosis factor (TNF), complement, nuclear factor kappa B (NF-κB), cathepsin, interleukin (IL), chemokine, serpin peptidase inhibitor, matrix metallopeptidase, innate immune cells, pattern recognition receptor (PRR), and other cytokine families. Our results indicate that Notch1a plays roles in inhibiting many immunity-related genes and could comprehensively mediate the innate immune response by regulating TLRs, nucleotide-binding-oligomerization-domain-like receptors (NLRs), lectins, complement, ILs, chemokines, TNF, cathepsin, and serpin. Further studies are required to understand the specific mechanism of Notch1a in innate immunity.

The protective effect of fish-derived cathelicidins on bacterial infections in zebrafish, Danio rerio

Antibiotic-resistant bacteria are severe threats to aquaculture industry. Boosting and modulating host immune responses has been proved to be an effective strategy to combat with bacterial infections and there is an urgent need for novel immunomodulators. Cathelicidins is an important family of host defense peptides (HDPs) that possess direct antimicrobial activities and potent immunomodulatory properties. Several cathelicidins have been identified and characterized from diverse fish species. Considering the relatively conserved immune systems between different fish species, it is reasonable to speculate that cathelicidins from different fish species possess immunomodulating functions on the other fish species. In the present study, two fish-derived cathelicidins (CATH_BRALE and codCath1) were selected to investigate their protective effect on zebrafish with bacterial infections. They exhibited potent and broad-spectrum antimicrobial activities against the tested aquatic Gram-positive and Gram-negative pathogenic bacteria, with MIC values ranging 2.34-18.75 μg/ml for CATH_BRALE and 2.34-37.5 μg/ml for codCath1. And their antimicrobial effect is so rapid that they killed the bacteria within 60 min. Unlike conventional antibiotics, they kill bacteria by inducing bacterial membrane permeabilization and cell disruption. Besides direct antimicrobial activity, CATH_BRALE and codCath1 exhibited potent immunomodulatory functions by both inhibiting bacteria induced zebrafish pro-inflammatory cytokine gene (TNF-α, IL-1β, and IL-6) expression and stimulating zebrafish chemokine gene IL-8 expression. In vivo challenge test proved that they could significantly decrease the bacterial numbers and enhance the survival rates of zebrafish. All the results above imply the great potential of CATH_BRALE and codCath1 as novel peptide immunomodulators in fish aquaculture industry.

The Mechanisms of Disease Caused by Acinetobacter baumannii

Acinetobacter baumannii is a Gram negative opportunistic pathogen that has demonstrated a significant insurgence in the prevalence of infections over recent decades. With only a limited number of “traditional” virulence factors, the mechanisms underlying the success of this pathogen remain of great interest. Major advances have been made in the tools, reagents, and models to study A. baumannii pathogenesis, and this has resulted in a substantial increase in knowledge. This article provides a comprehensive review of the bacterial virulence factors, the host immune responses, and animal models applicable for the study of this important human pathogen. Collating the most recent evidence characterizing bacterial virulence factors, their cellular targets and genetic regulation, we have encompassed numerous aspects important to the success of this pathogen, including membrane proteins and cell surface adaptations promoting immune evasion, mechanisms for nutrient acquisition and community interactions. The role of innate and adaptive immune responses is reviewed and areas of paucity in our understanding are highlighted. Finally, with the vast expansion of available animal models over recent years, we have evaluated those suitable for use in the study of Acinetobacter disease, discussing their advantages and limitations.

AcuD Gene Knockout Attenuates the Virulence of Talaromyces marneffei in a Zebrafish Model

Talaromyces marneffei is the only dimorphic species in its genus and causes a fatal systemic mycosis named talaromycosis. Our previous study indicated that knockdown of AcuD gene (encodes isocitrate lyase of glyoxylate bypass) of T. marneffei by RNA interference approach attenuated the virulence of T. marneffei, while the virulence of the AcuD knockout strains was not studied. In this study, T. marneffei-zebrafish infection model was successfully established through hindbrain microinjection with different amounts of T. marneffei yeast cells. After co-incubated at 28°C, the increasing T. marneffei inoculum doses result in greater larval mortality; and hyphae generation might be one virulence factor involved in T. marneffei-zebrafish infection. Moreover, the results demonstrated that the virulence of the ΔAcuD was significantly attenuated in this Zebrafish infection model.

The protective efficacy of four iron-related recombinant proteins and their single-walled carbon nanotube encapsulated counterparts against Aeromonas hydrophila infection in zebrafish

Iron-related proteins play important roles in iron homeostasis, and they may be potential vaccine candidates against pathogenic Aeromonas hydrophila. In addition, the encapsulation of antigens in single-walled carbon nanotubes (SWCNTs) has recently been shown to effectively stimulate the host immune response. To investigate the immune response of zebrafish to iron-related proteins and SWCNT-encapsulated proteins, we overexpressed and purified four iron-related recombinant proteins (P55870, A0KGK5, A0KPP0, and A0KIY3) from A. hydrophila. We then vaccinated zebrafish with these proteins and their SWCNT-encapsulated counterparts via both intraperitoneal injection and bath immunization. The target proteins evoked an immune response in zebrafish after intraperitoneal injection, and SWCNT-encapsulation significantly increased the immune response after bath immunization. When challenged with virulent A. hydrophila, zebrafish administered 5 μg intraperitoneal injections of SWCNT-P55870, A0KGK5, A0KPP0, or A0KIY3 had remarkably high relative percent survivals (RPSs) (50%, 55.6%, 66.7%, and 94.44% respectively). The RPSs of zebrafish vaccinated via immunization bath with 40 mg/L SWCNT-encapsulated counterparts were also high (52.94%, 55.56%, 61.11%, and 86.11%, respectively). These results indicated that zebrafish vaccinated with P55870, A0KGK5, SWCNT-P55870, and SWCNT-A0KGK5 were partially protected, while A0KPP0 and A0KIY3 were promising vaccine candidates against pathogenic A. hydrophila infection.

Mycobacteria employ two different mechanisms to cross the blood-brain barrier

Central nervous system (CNS) infection by Mycobacterium tuberculosis is one of the most devastating complications of tuberculosis, in particular in early childhood. In order to induce CNS infection, M. tuberculosis needs to cross specialised barriers protecting the brain. How M. tuberculosis crosses the blood-brain barrier (BBB) and enters the CNS is not well understood. Here, we use transparent zebrafish larvae and the closely related pathogen Mycobacterium marinum to answer this question. We show that in the early stages of development, mycobacteria rapidly infect brain tissue, either as free mycobacteria or within circulating macrophages. After the formation of a functionally intact BBB, the infiltration of brain tissue by infected macrophages is delayed, but not blocked, suggesting that crossing the BBB via phagocytic cells is one of the mechanisms used by mycobacteria to invade the CNS. Interestingly, depletion of phagocytic cells did not prevent M. marinum from infecting the brain tissue, indicating that free mycobacteria can independently cause brain infection. Detailed analysis showed that mycobacteria are able to cause vasculitis by extracellular outgrowth in the smaller blood vessels and by infecting endothelial cells. Importantly, we could show that this second mechanism is an active process that depends on an intact ESX-1 secretion system, which extends the role of ESX-1 secretion beyond the macrophage infection cycle.

Microfluidics for mechanobiology of model organisms

Mechanical stimuli play a critical role in organ development, tissue homeostasis, and disease. Understanding how mechanical signals are processed in multicellular model systems is critical for connecting cellular processes to tissue- and organism-level responses. However, progress in the field that studies these phenomena, mechanobiology, has been limited by lack of appropriate experimental techniques for applying repeatable mechanical stimuli to intact organs and model organisms. Microfluidic platforms, a subgroup of microsystems that use liquid flow for manipulation of objects, are a promising tool for studying mechanobiology of small model organisms due to their size scale and ease of customization. In this work, we describe design considerations involved in developing a microfluidic device for studying mechanobiology. Then, focusing on worms, fruit flies, and zebrafish, we review current microfluidic platforms for mechanobiology of multicellular model organisms and their tissues and highlight research opportunities in this developing field.

Cross-reactivity of monoclonal antibodies against CD4-1 and CD8α of ginbuna crucian carp with lymphocytes of zebrafish and other cyprinid species

We have monoclonal antibodies (mAbs) against CD4-1 (6D1) and CD8α (2C3) in ginbuna crucian carp Carassius auratus langsdorfii. In our previous studies we showed that 2C3 mAb positive cells are the primary cell type showing specific cytotoxicity against allogeneic targets, suggesting that CD8α⁺ lymphocytes in ginbuna are equivalent to cytotoxic T lymphocytes (CTLs) in mammals. We further demonstrated the helper T cell function of 6D1 mAb positive cells by studying mixed leukocyte culture (MLC) and hapten/carrier effects. Here, we report that our mAbs cross-react with zebrafish lymphocytes. First, mAbs 6D1 and 2C3 recognized 7-11% of zebrafish lymphocytes that were ZAP-70 positive and had the typical morphology of lymphocytes. Second, to verify the cell types reacting with the 6D1 and 2C3 mAbs we examined the expression profiles of zebrafish lymphocyte surface markers in FACS-sorted lymphocytes from kidney. cd4-1 (cd8a) and tcrac but not iglc transcripts were detected in 6D1(2C3)⁺ lymphocytes, whereas cd4-1 (cd8a) transcripts were not found in 6D1 (2C3)^- lymphocytes. Third, we further confirmed that 6D1 reacted with zebrafish CD4-1 but not CD4-2, and 2C3 recognized zebrafish CD8α expressed on HEK293T cells. Collectively, these findings suggest that 6D1⁺ and 2C3⁺ lymphocytes in zebrafish are equivalent to CD4⁺ and CD8α⁺ T lymphocytes in mammals, respectively. Furthermore, we found the cross-reactivity of our 6D1 and 2C3 mAbs with other cyprinid species including goldfish, common carp and grass carp.

Goldfish, Carassius auratus, as an infection model for studying the pathogenesis of Edwardsiella piscicida

This study demonstrates the feasibility of using goldfish as an infection model to investigate the pathogenesis of Edwardsiella piscicida. Goldfish were found to be susceptible to acute E. piscicida-induced disease and died in a dose-dependent manner. E. piscicida was further shown to replicate rapidly in the head kidneys and livers of infected goldfish from 1 d post-injection, and bacteria numbers were significantly decreased 5 d post-injection. Immune responses were successfully induced in goldfish injected with E. piscicida strains and 60% of goldfish inoculated with an attenuated E. piscicida strain were found to survive subsequent injection with a pathogenic strain. The results of differential leukocyte count experiments suggested that leukocytes were immediately recruited as an innate immune response against the infection. Thus, this well-characterized goldfish species is a suitable infection model for studying E. piscicida pathogenesis, and might be applicable to research on other fish diseases.

A fluorescence-based reporter for monitoring expression of mycobacterial cytochrome bd in response to antibacterials and during infection

Cytochrome bd is a component of the oxidative phosphorylation pathway in many Gram-positive and Gram-negative bacteria. Next to its role as a terminal oxidase in the respiratory chain this enzyme plays an important role as a survival factor in the bacterial stress response. In Mycobacterium tuberculosis and related mycobacterial strains, cytochrome bd is an important component of the defense system against antibacterial drugs. In this report we describe and evaluate an mCherry-based fluorescent reporter for detection of cytochrome bd expression in Mycobacterium marinum. Cytochrome bd was induced by mycolic acid biosynthesis inhibitors such as isoniazid and most prominently by drugs targeting oxidative phosphorylation. We observed no induction by inhibitors of protein-, DNA- or RNA-synthesis. The constructed expression reporter was suitable for monitoring mycobacterial cytochrome bd expression during mouse macrophage infection and in a zebrafish embryo infection model when using Mycobacterium marinum. Interestingly, in both these infection models cytochrome bd levels were considerably higher than during in vitro culturing of M. marinum. The expression reporter described here can be a valuable tool for elucidating the role of cytochrome bd as a survival factor.

Acetazolamide Inhibits the Level of Tyrosinase and Melanin: An Enzyme Kinetic, In Vitro, In Vivo, and In Silico Studies

Melanin is the major factor that determines skin color and protects from ultraviolet radiation. In present study we evaluated the anti-melanogenesis effect of acetazolamide (ACZ) using four different approaches: enzyme kinetic, in vitro, in vivo and in silico. ACZ demonstrated significant inhibitory activity (IC50 7.895 ± 0.24 μm) against tyrosinase as compared to the standard drug kojic acid (IC50 16.84 ± 0.64 μm) and kinetic analyses showed that ACZ is a non-competitive inhibitor without cytotoxic effect. In in vitro experiments, A375 human melanoma cells were treated with 20 or 40 μm of ACZ with or without 50 μm of l-DOPA. Western blot results showed that ACZ significantly (P < 0.05) decreased the expression level of tyrosinase at 40 μm. Zebrafish embryos were treated with 10, 20 or 40 μm of ACZ and of positive control kojic acid. At 72 h of treatment with ACZ and kojic acid, ACZ significantly (P < 0.001) decreased the embryos pigmentation to 40.8% of untreated embryos at the dose of 40 μm of ACZ while kojic acid decreased only 25.0% of pigmentation at the same dose of kojic acid. In silico docking were performed against tyrosinase using PyRx tool. Docking studies suggested that His244, Asn260 and His85 are the major interacting residues in the binding site of the protein. In conclusion, our results suggest that ACZ is a good candidate for the inhibition of melanin and it could be used as a lead for developing the drugs for hyperpigmentary disorders and skin whitening.

Membrane vesicles from Piscirickettsia salmonis induce protective immunity and reduce development of salmonid rickettsial septicemia in an adult zebrafish model

Infections caused by the facultative intracellular bacterial pathogen Piscirickettsia salmonis remains an unsolved problem for the aquaculture as no efficient treatments have been developed. As a result, substantial amounts of antibiotic have been used to limit salmonid rickettsial septicemia (SRS) disease outbreaks. The antibiotic usage has not reduced the occurrence, but lead to an increase in resistant strains, underlining the need for new treatment strategies. P. salmonis produce membrane vesicles (MVs); small spherical structures know to contain a variety of bacterial components, including proteins, lipopolysaccharides (LPS), DNA and RNA. MVs mimics' in many aspects their mother cell, and has been reported as alternative vaccine candidates. Here, MVs from P. salmonis was isolated and evaluated as a vaccine candidate against SRS in an adult zebrafish infection model. When zebrafish was immunized with MVs they were protected from subsequent challenge with a lethal dose of P. salmonis. Histological analysis showed a reduced bacterial load upon challenge in the MV immunized group, and the mRNA expression levels of several immune related genes altered, including mpeg1.1, tnfα, il1b, il10 and il6. The MVs induced the secretion of IgM upon immunization, indicating an immunogenic effect of the vesicles. Taken together, the data demonstrate a vaccine potential of MVs against P. salmonis.

Zebrafish models for functional and toxicological screening of nanoscale drug delivery systems: promoting preclinical applications

Preclinical screening with animal models is an important initial step in clinical translation of new drug delivery systems. However, establishing efficacy, biodistribution, and biotoxicity of complex, multicomponent systems in small animal models can be expensive and time-consuming. Zebrafish models represent an alternative for preclinical studies for nanoscale drug delivery systems. These models allow easy optical imaging, large sample size, and organ-specific studies, and hence an increasing number of preclinical studies are employing zebrafish models. In this review, we introduce various models and discuss recent studies of nanoscale drug delivery systems in zebrafish models. Also in the end, we proposed a guideline for the preclinical trials to accelerate the progress in this field.

Rhein attenuates inflammation through inhibition of NF-κB and NALP3 inflammasome in vivo and in vitro

Rhein is an important component in traditional Chinese herbal medicine formulations for gastrointestinal disorders, including inflammatory bowel diseases such as ulcerative colitis. In this study, we investigated the beneficial effects of rhein in inflammation models in the transgenic zebrafish line TG (corolla eGFP), in which both macrophages and neutrophils express eGFP and RAW264.7 macrophages. We found that the tail-cutting-induced migration of immune cells was significantly reduced in transgenic zebrafish treated with rhein. In addition, the production of proinflammatory cytokines, including IL-6, IL-1β, and tumor necrosis factor-α, were significantly reduced in lipopolysaccharide (LPS)-induced RAW264.7 macrophages treated with rhein. Parallel to the inhibition of proinflammatory cytokines, rhein significantly reduced phosphorylation levels of NF-κB p65 and inducible nitric oxide synthase, as well as COX-2 protein expression levels. Furthermore, rhein significantly reduced NALP3 and cleaved IL-1β expression in LPS + ATP-induced RAW264.7 macrophages. Thus, the present study demonstrates that rhein may exhibit its anti-inflammatory action via inhibition of NF-κB and NALP3 inflammasome pathways.

In vitro, in vivo and in silico anti-hyperglycemic inhibition by sinigrin

OBJECTIVE

To evaluate the anti-hyperglycemic potential of sinigrin using in vitro, in silico and in vivo streptozotocin (STZ) induced hyperglycemic zebrafish model.

METHODS

The in vitro enzyme inhibition assay was carried out to determine the IC₅₀ value against α-glucosidase and α-amylase, in silico molecular docking was performed against both enzymes with PyRx tool and simulations were performed using GROMACS tool. Hyperglycemia was induced in zebrafishes using three intraperitoneal injections on alternating days for 1 week at 350 mg/kg of STZ. Hyperglycemic fishes were treated intraperitoneally with 50, 100 and 150 mg of sinigrin/kg of body weight for 24 h and glucose levels were measured.

RESULTS

The sinigrin showed very strong inhibition against α-glucosidase and α-amylase with 0.248 and 0.00124 μM while reference drug acarbose showed IC₅₀ value of 73.0700 and 0.0017 μM against α-glucosidase and α-amylase, respectively. Kinetic analysis revealed that sinigrin has the mixed type mode of inhibition against α-glucosidase. Molecular docking results revealed its strong binding affinity with α-glucosidase (-10.00 kcal/mol) and α-amylase (-8.10 kcal/mol). Simulations graphs confirmed its stability against both enzymes. Furthermore, in hyperglycemic zebrafishes most significant (P < 0.001) reduction of glucose was occurred at 150 mg/kg, moderate significant reduction of glucose was observed at 100 mg/kg and no any significant reduction of glucose was measured at 50 mg/kg.

CONCLUSIONS

It can be evident from the present results that sinigrin has potent anti-hyperglycemic activity and it may prove to be effective treatment for the hyperglycemia.

ToF-SIMS Parallel Imaging MS/MS of Lipid Species in Thin Tissue Sections

Unambiguous identification of detected species is essential in complex biomedical samples. To date, there are not many mass spectrometry imaging techniques that can provide both high spatial resolution and identification capabilities. A new and patented imaging tandem mass spectrometer, exploiting the unique characteristics of the nanoTOF II (Physical Electronics, USA) TOF-SIMS TRIFT instrument, was developed to address this.Tandem mass spectrometry is based on the selection of precursor ions from the full secondary ion spectrum (MS¹), followed by energetic activation and fragmentation, and collection of the fragment ions to obtain a tandem MS spectrum (MS²). The PHI NanoTOF II mass spectrometer is equipped with a high-energy collision induced dissociation (CID) fragmentation cell as well as a second time-of-flight analyzer developed for simultaneous ToF-SIMS and tandem MS imaging experiments.We describe here the results of a ToF-SIMS imaging experiment on a thin tissue section of an infected zebrafish as a model organism for tuberculosis. The focus is on the obtained ion distribution plot of a fatty acid as well as its identification by tandem mass spectrometry.

Comparative Analysis of Membrane Vesicles from Three Piscirickettsia salmonis Isolates Reveals Differences in Vesicle Characteristics

Membrane vesicles (MVs) are spherical particles naturally released from the membrane of Gram-negative bacteria. Bacterial MV production is associated with a range of phenotypes including biofilm formation, horizontal gene transfer, toxin delivery, modulation of host immune responses and virulence. This study reports comparative profiling of MVs from bacterial strains isolated from three widely disperse geographical areas. Mass spectrometry identified 119, 159 and 142 proteins in MVs from three different strains of Piscirickettsia salmonis isolated from salmonids in Chile (LF-89), Norway (NVI 5692) and Canada (NVI 5892), respectively. MV comparison revealed several strain-specific differences related to higher virulence capability for LF-89 MVs, both in vivo and in vitro, and stronger similarities between the NVI 5692 and NVI 5892 MV proteome. The MVs were similar in size and appearance as analyzed by electron microscopy and dynamic light scattering. The MVs from all three strains were internalized by both commercial and primary immune cell cultures, which suggest a potential role of the MVs in the bacterium’s utilization of leukocytes. When MVs were injected into an adult zebrafish infection model, an upregulation of several pro-inflammatory genes were observed in spleen and kidney, indicating a modulating effect on the immune system. The present study is the first comparative analysis of P. salmonis derived MVs, highlighting strain-specific vesicle characteristics. The results further illustrate that the MV proteome from one bacterial strain is not representative of all bacterial strains within one species.

Infection of zebrafish embryos with live fluorescent Streptococcus pneumoniae as a real-time pneumococcal meningitis model

BACKGROUND

Streptococcus pneumoniae is one of the most important causes of bacterial meningitis, an infection where unfavourable outcome is driven by bacterial and host-derived toxins. In this study, we developed and characterized a pneumococcal meningitis model in zebrafish embryos that allows for real-time investigation of early host-microbe interaction.

METHODS

Zebrafish embryos were infected in the caudal vein or hindbrain ventricle with green fluorescent wild-type S. pneumoniae D39 or a pneumolysin-deficient mutant. The kdrl:mCherry transgenic zebrafish line was used to visualize the blood vessels, whereas phagocytic cells were visualized by staining with far red anti-L-plastin or in mpx:GFP/mpeg1:mCherry zebrafish, that have green fluorescent neutrophils and red fluorescent macrophages. Imaging was performed by fluorescence confocal and time-lapse microscopy.

RESULTS

After infection by caudal vein, we saw focal clogging of the pneumococci in the blood vessels and migration of bacteria through the blood-brain barrier into the subarachnoid space and brain tissue. Infection with pneumolysin-deficient S. pneumoniae in the hindbrain ventricle showed attenuated growth and migration through the brain as compared to the wild-type strain. Time-lapse and confocal imaging revealed that the initial innate immune response to S. pneumoniae in the subarachnoid space mainly consisted of neutrophils and that pneumolysin-mediated cytolytic activity caused a marked reduction of phagocytes.

CONCLUSIONS

This new meningitis model permits detailed analysis and visualization of host-microbe interaction in pneumococcal meningitis in real time and is a very promising tool to further our insights in the pathogenesis of pneumococcal meningitis.

Prophylactic administration of chicken cathelicidin-2 boosts zebrafish embryonic innate immunity

Chicken cathelicidin-2 (CATH-2) is a host defense peptide that exhibits immunomodulatory and antibacterial properties. Here we examined effects of CATH-2 in zebrafish embryos in the absence and presence of infection. Yolk-injection of 0.2-1.5 h post-fertilized (hpf) zebrafish embryos with 2.6 ng/kg CATH-2 increased proliferation of phagocytic cells at 48 hpf by 30%. A lethal infection model was developed to test the prophylactic protective effect of CATH-2 peptide. Embryos (0.2-1.5 hpf) were injected with 2.6 ng/kg CATH-2, challenged with a lethal dose of fluorescently labeled Salmonella enteritidis pGMDs3 at 28 hpf and monitored for survival. Prophylactic treatment with CATH-2 was found to delay infection starting at 22 h post-infection (hpi). At 18-20 hpi, significantly lower (2-fold) fluorescence intensity and decreased bacterial loads were detected in peptide-treated embryos. Thus prophylactic administration of low CATH-2 concentrations confer partial protection in zebrafish embryos by boosting the innate immune system.

Leptospiral outer membrane protein LipL32 induces inflammation and kidney injury in zebrafish larvae

Leptospirosis is an often overlooked cause of acute kidney injury that can lead to multiple organ failure and even death. The principle protein that conserved in many pathogenic leptospires is the outer membrane protein LipL32. However, the role of LipL32 in the pathogenesis of renal injury in leptospirosis is not entirely clear. Here we studied the effects of LipL32 on the developing kidney in zebrafish larvae. Incubation of zebrafish larvae with Leptospira santarosai serovar Shermani induced acute tubular injury predominantly in the proximal pronephric ducts. Furthermore, microinjection of lipl32 mRNA or recombinant LipL32 protein into zebrafish larvae increased macrophage accumulation and disrupted the basolateral location of NA-K-ATPase in pronephric ducts. These changes led to substantial impairment of the pronephric kidney structure. We further demonstrated that morpholino knockdown of tlr2, but not tlr4, reduced the LipL32-induced leukocyte infiltration and kidney injury. These data demonstrate that LipL32 contributes to the renal pathology in leptospirosis and gives some clues to the potential virulence of LipL32. Our results support the use of zebrafish as a model organism for studying the disease mechanism of leptospiral infection. This model might permit the future exploration of the virulence and molecular pathways of different leptospiral outer membrane proteins.

A Zebrafish Larval Model to Assess Virulence of Porcine Streptococcus suis Strains

Streptococcus suis is an encapsulated Gram-positive bacterium, and the leading cause of sepsis and meningitis in young pigs resulting in considerable economic losses in the porcine industry. It is also considered an emerging zoonotic agent. In the environment, both avirulent and virulent strains occur in pigs, and virulent strains appear to cause disease in both humans and pigs. There is a need for a convenient, reliable and standardized animal model to assess S. suis virulence. A zebrafish (Danio rerio) larvae infection model has several advantages, including transparency of larvae, low cost, ease of use and exemption from ethical legislation up to 6 days post fertilization, but has not been previously established as a model for S. suis. Microinjection of different porcine strains of S. suis in zebrafish larvae resulted in highly reproducible dose- and strain-dependent larval death, strongly correlating with presence of the S. suis capsule and to the original virulence of the strain in pigs. Additionally we compared the virulence of the two-component system mutant of ciaRH, which is attenuated for virulence in both mice and pigs in vivo. Infection of larvae with the ΔciaRH strain resulted in significantly higher survival rate compared to infection with the S10 wild-type strain. Our data demonstrate that zebrafish larvae are a rapid and reliable model to assess the virulence of clinical porcine S. suis isolates.