Veronii Infection Research Articles

Aeromonas veronii-associated bacteremia in the course of treatment of acute myeloid leukemia: a case report and review of the literature

PurposeThis study aimed to report a case of acute myeloid leukemia (AML) complicated by Aeromonas veronii infection-induced bacteremia and to review relevant literature on the etiology, prevention, treatment, and prognosis of bacteremia in immunocompromised populations, aiming to reduce mortality in individuals with hematologic and other end-stage diseases and improve patient outcomes.Methods and resultsWe reported the case of a 23-year-old male patient with relapsed AML characterized by AML1:ETO and ASXL positivity, classified as a high-risk group. The patient presented with fever, abdominal pain, diarrhea, nausea, and vomiting after consuming partially cooked fish. The patient was admitted with high leucocytes, C-reactive protein, procalcitonin, and interleukin-6 levels. Peripheral blood high-throughput sequencing (Next-Generation Sequencing NGS) confirmed infection with Aeromonas veronii, while an abdominal CT scan indicated a liver abscess with gas formation. Culture of the drainage fluid from the ultrasound-guided liver abscess puncture demonstrated growth of Aeromonas veronii. Based on the sensitivity results, the patient was treated with intravenous ciprofloxacin and cefoperazone-sulbactam. After treatment with antibiotics, blood transfusion, liver protection, and azacitidine 100 mg ih, combined with dry white sand(interferon alpha-1B, interleukin-2, and thalidomide), the critical condition of the patient improved, and he was discharged. This study was approved by the Ethics Committee of Medical Research in the Second Affiliated Hospital of Henan University of Science and Technology. Informed consent was obtained from this patient and we have obscured the patient's identifying information. All methods were carried out in accordance with relevant guidelines and regulations.ConclusionWhen patients with a recurrence of AML have a history of consuming or contacting aquatic products, clinicians should be vigilant about Aeromonas veronii infection. The presence of Aeromonas veronii in peripheral blood must alert clinicians to the possibility of severe sepsis and septic shock. Early diagnosis and prompt treatment are crucial to reducing patient mortality.

Interleukin-17B in common carp (Cyprinus carpio L.): Molecular cloning and immune effects as immune adjuvant of Aeromonas veronii formalin-killed vaccine

The interleukin-17 (IL-17) family of cytokines is critical for host defense responses and mediates different pro- or anti-inflammatory mediators through different signaling pathways. However, the function of the related family member, IL-17B, in teleosts is poorly understood. In the present study, an IL-17B homolog (CcIL-17B) in common carp (Cyprinus carpio) was identified, and sequence analysis showed that CcIL-17B had eight conserved cysteine residues, four of which could form two pairs of disulfide bonds, which in turn formed a ring structure composed of nine amino acids (aa). The deduced aa sequences of CcIL-17B shared 35.79–92.93 % identify with known homologs. The expression patterns were characterized in healthy and bacteria-infected carp. In healthy carp, IL-17B mRNA was highly expressed in the spleen, whereas Aeromonas veronii effectively induced CcIL-17B expression in the liver, head, kidney, gills, and intestine. The recombinant protein rCcIL-17B could regulate the expression levels of inflammatory cytokines (such as IL-1β, IL-6, TNF-α, and IFN-γ) in primary cultured head kidney leukocytes in vitro. As an adjuvant for the formalin-killed A. veronii (FKA) vaccine, rCcIL-17B induced the production of specific antibodies more rapidly and effectively than Freund's complete adjuvant (FCA). The results of the challenge experiments showed that the relative percent survival (RPS) after vaccination with rCcIL-17B was 78.13 %. This percentage was significantly elevated compared to that observed in the alternative experimental groups (62.5 % and 37.5 %, respectively). Additionally, the bacterial loads in the spleen of the rCcIL-17B + FKA group were significantly lower than those in the control group from 12 h to 48 h after bacterial infection. Furthermore, histological analysis showed that the epithelial cells were largely intact, and the striated border structure was complete in the intestine of rCcIL-17B + FKA group. Collectively, our results demonstrate that CcIL-17B plays a crucial role in eliciting immune responses and evokes a higher RPS against A. veronii challenge compared to the traditional adjuvant FCA, indicating that rCcIL-17B is a promising vaccine adjuvant for controlling A. veronii infection.

Multiomics Analyses Explore the Immunometabolic Interplay in the Liver of White Crucian Carp (Carassius cuvieri) After Aeromonas veronii Challenge.

Aeromonas veronii is one of the predominant pathogenic species that can imperil the survival of farmed fish. However, the interactive networks of immune regulation and metabolic response in A. veronii-infected fish are still unclear. In this investigation, we aimed to explore immunometabolic interplay in white crucian carp (WCC) after the A. veronii challenge. Elevated levels of immune-related genes were observed in various tissues after A. veronii infection, along with the sharp alteration of disease-related enzymatic activities. Besides, decreased levels of antioxidant status were observed in the liver, but most metabolic gene expressions increased dramatically. Multiomics analyses revealed that metabolic products of amino acids, such as formiminoglutamic acid (FIGLU), L-glutamate (L-Glu), and 4-hydroxyhippuric acid, were considered the crucial liver biomarkers in A. veronii-infected WCC. In addition, A. veronii infection may dysregulate endoplasmic reticulum (ER) function to affect the metabolic process of lipids, carbohydrates, and amino acids in the liver of WCC. These results may have a comprehensive implication for understanding immunometabolic response in WCC upon A. veronii infection.

Pichia pastoris composition expressed aerolysin mutant of Aeromonas veronii as an oral vaccine evaluated in zebrafish (Danio rerio)

Vaccines are one of the most practical means to stop the spreading of Aeromonas veronii in aquaculture. In this study, virulence factor aerolysin mutant NTaer which has lost its hemolytic activity was used as a target antigen. Pichia pastoris constitutive secretory expression NTaer (GS115-NTaer) was used as a potential safe oral vaccine to evaluate its effectiveness on zebrafish immunity. The result shows that vaccination of GS115- NTaer for four weeks did not affect the growth performance of the host, while eliciting an effective immune protective response. Compared with the control group, the GS115-NTaer could significantly up-regulate the relative expression level of the intestinal tight junction protein 1α (TJP1α) gene, and significantly increased the contents of lysozyme (LYZ), complement C3 and C4 in the gut, indicating that the innate immune response of the fish was activated. The relative gene expression levels of macrophage-expressed gene 1 (MPEG1) and T cell receptor (TCR-α) in the gut, and MPEG1, CD4, CD8, TCR-α, GATA3, and T-bet in the spleen were all increased significantly, indicating that the cellular immune response of the fish was activated. Furthermore, the contents of serum IgM and intestinal mucosa IgZ antibodies were significantly increased, which showed that humoral immunity was also activated. Moreover, inoculation with GS115-NTaer significantly changed the structure of gut microbiota. In particular, the relative ratio of (Firmicutes + Fusobacteriota + Bacteroidota)/Proteobacteria was significantly higher than that of the control and GS115 groups. Lastly, the vaccinated fish were challenged with A. veronii, and the relative percent survival of GS115 and the GS115-NTear groups was 14.28% and 33.43%. This improvement of immunity was not only due to the specific immune response but also attributed to the improvement of innate immunity and the gut microbiota which was demonstrated by the germ-free zebrafish model. Collectively, this study provides information on the effectiveness of GS115-NTear as an oral vaccine for the green prevention and control of A. veronii infection in fish aquaculture.

Susceptibility and host immune response comparison between Siniperca chuatsi and Siniperca scherzeri infected by Aeromonas veronii

The bacterial hemorrhagic septicemia caused by Aeromonas veronii is a highly contagious disease leading to high mortality in various aquatic animals, which has become one of the most serious diseases in mandarin fish, Siniperca chuatsi and Siniperca scherzeri. The difference of susceptibility and host immune response between S. chuatsi and S. scherzeri to A. veronii has not been revealed. In this study, the calculated LD50 of A. veronii SJ4 to S. chuatsi and S. scherzeri was 3.8 × 105 CFU/ mL and 4.8 × 106 CFU/mL, respectively, indicating S. chuatsi displays more susceptible to A. veronii than S. scherzeri. The differences of immune response between S. chuatsi and S. scherzeri infected by A. veronii SJ4 was analyzed by transcriptome technology. A total of 6010 and 1676 differentially expressed genes (DEGs) of kidneys were detected in the S. scherzeri experimental group (S-S-E/C) and S. chuatsi experimental group (S-C-E/C) at the 12 hpi, respectively. GO and KEGG functional analysis of DEGs indicated that numerous enriched immune terms were mainly related to antigen processing and presentation, toll-like receptor signaling, and C-type lectin receptor signaling. 8 DEGs (CLE, HSP90, IL6, MHC I, MHC II, RAS, TLR5 and TLR9) were selected from these immune related pathways, and the spatiotemporal expression of these DEGs in S. chuatsi and S. scherzeri were evaluated and compared. The results showed that CLE, HSP90, IL6, MHC I, MHC II, RAS, TLR5 and TLR9 in S. scherzeri after A. veronii infection were significantly up-regulated than in S. chuatsi. Our results indicated that these immune-related genes may exert a pivotal role during the initial phase of infection, and the priming speed of these immune-related genes lead to the differences in host immunity. This study screened the potential genes and pathways which involved in the immune response of mandarin fish, which helps for further understanding on fish immune. By selecting immune-related genes and comparing the immune mechanisms of S. chuatsi and S. scherzeri at the transcriptome level, the research offers new insights for the genetic breeding of Siniperca species to enhance infection resistance.

Integration analysis of miRNA-mRNA uncovers the molecular immune mechanism of macrophage response to Aeromonas veronii infection

Macrophages are innate immunity cells which play pivotal roles in infectious immunity. Aeromonas veronii is a zoonotic agent capable of causing sepsis and poses a serious threat to public health. However, few studies have focused on miRNA-mRNA integration analysis to address the immune mechanisms of macrophage response to A. veronii infection. Herein, we characterized the immunophysiological, biochemical, and transcriptome changes of macrophage under A. veronii infection. We found that macrophages infected with A. veronii released large amounts of cytokines and triggered NLRP3-dependent pyroptosis. Subsequently, 603 differentially expressed miRNAs (DEMIs) and 3693 differentially expressed mRNAs (DEMs) were identified by RNA-seq analysis under A. veronii infection. Moreover, integrated analysis of miRNA-mRNA yielded 66 miRNA-target gene pairs composed of 41 DEMIs and 27 DEMs. We next identified the Toll-like receptor, NOD-like receptor, TNF and NF-κB pathways as necessary for macrophage to respond to A. veronii infection. miR-847 and miR-627 were involved in macrophage response to A. veronii infection by negatively regulating Pannexin-1 and thioredoxin interacting protein (TXNIP). Our findings elucidate the molecular mechanism of macrophage response to A. veronii infection at the miRNA level, providing many candidate miRNAs and mRNAs therapeutic targets for the prevention and treatment of A. veornii infectious diseases.

Comparative analysis of the structural and compositional change of spotted sea bass (Lateolabrax maculatus) gut microflora following Aeromonas veronii infection and the effects of Lactobacillus plantarum on these changes

Growing evidence suggests a close relationship between gut microbiota and infectious diseases. However, the specific role of gut microbiota in host-pathogen interactions during aquaculture-related infections remains poorly understood. This study investigated the diversity and composition of gut microbiota communities in Aeromonas veronii-infected Lateolabrax maculatus using high-throughput sequencing. The results revealed significant changes in the structure and composition of L. maculatus gut microbiota after A. veronii infection. Over time, Bacteroidetes and Firmicutes decreased significantly, while Proteobacteria increased significantly after A. veronii infection. Most intestinal bacteria showed a decline in abundance over time, with probiotics (such as Lactobacillus) experiencing a significant decrease and pathogens (such as Aeromonas) showing a significant increase. Conversely, no differences were observed in the structure and composition of gut microbiota between healthy L. maculatus and those infected with A. veronii after treatment with Lactobacillus plantarum; no changes in relative abundances of other bacterial phyla or genera except for Aeromonas. Furthermore, intestinal flora’s structural diversity and composition differed significantly from untreated L. maculatus infected with A. veronii. These findings suggest alterations in the structure and composition of gut microbiota following A. veronii infection. L. plantarum can maintain a dynamic balance within the intestinal flora, reducing the potential risk of pathogen infections.

Interleukin-1 beta (IL-1β) as adjuvant enhances the immune effects of Aeromonas veronii inactivated vaccine in largemouth bass (Micropterus salmoides)

Largemouth bass (Micropterus salmoides) has emerged as a significant economic fish species, with a rise in Aeromonas veronii infections in farming. However, research on adjuvants for vaccines against A. veronii in largemouth bass remains scarce. In present study, recombinant largemouth bass IL-1β (LbIL-1β) was expressed to explore its adjuvant effect on the A. veronii inactivated vaccine. Following vaccination with recombinant LbIL-1β (rLbIL-1β) and the inactivated A. veronii, higher serum SOD levels and lysozyme activities were observed in largemouth bass from inactivated A. veronii + rLbIL-1β vaccinated group. Furthermore, it was discovered that rLbIL-1β was able to boost the serum-specific antibody levels induced by the inactivated A. veronii. The qRT-PCR analysis revealed that rLbIL-1β also enhanced the expression of IgM, CD4, and MHC II in largemouth bass triggered by the inactivated A. veronii. After challenged with live A. veronii, the outcomes demonstrated that the relative percentage survival (RPS) for largemouth bass resulting from the inactivated A. veronii in combination with rLbIL-1β was 76.67 %, surpassing the RPS of 60 % in the inactivated A. veronii group. Collectively, these findings indicate that rLbIL-1β enhances the protective effect of the A. veronii inactivated vaccine on largemouth bass, showcasing potential as an adjuvant for further development.

The therapeutic role of Azadirachta indica leaves ethanolic extract against detrimental effects of Aeromonas veronii infection in Nile tilapia, Oreochromis niloticus.

Bacterial pathogens cause high fish mortalities and in turn economic losses in fish farms. Innovative strategies should be applied to control bacterial infections instead of antibiotics to avoid the resistance problem. Consequently, the present investigation studied the curative potential of Azadirachta indica leave ethanolic extract (AILEE) on Aeromonas veronii infection in Oreochromis niloticus. A preliminary trial was assessed to evaluate the curative dose of AILEE which was found to be 2.5mg/L. One hundred and sixty fish were divided into equal four groups in four replications, where group 1 and group 2 were non-challenged and treated with 0- and 2.5-mg/L AILEE, respectively. Group 3 and group 4 were challenged with A. veronii and treated with 0- and 2.5-mg/L AILEE, respectively for 10days. A. veronii infection produced severe clinical manifestations and a high mortality rate in the infected fish. Furthermore, the infected fish exhibited a significant rise in the hepatorenal indices (aspartate aminotransferase, alanine aminotransferase, and creatinine), the oxidant biomarker (malondialdehyde), and the stress indicators (glucose and cortisol). A significant reduction in the protein profile and antioxidant/immune parameters (catalase, immunoglobulin M, lysozyme, nitric oxide, and phagocytic activity) was observed in the infected fish. Water application of the infected group to 2.5-mg/L AILEE notably ameliorated the hepatorenal indices, the oxidant biomarker, and the stress indicators. Furthermore, AILEE improved the antioxidant/immune indices. Water application of 2.5-mg/L AILEE could be useful against A. veronii infection in O. niloticus culture.

Systematic identification and analysis of immune-related circRNAs of Pelteobagrus fulvidraco involved in Aeromonas veronii infection

Circular RNA (circRNA) represents a type of newly discovered non-coding RNA, distinguished by its closed loop structure formed through covalent bonds. Recent studies have revealed that circRNAs have crucial influences on host anti-pathogen responses. Yellow catfish (Pelteobagrus fulvidraco), an important aquaculture fish with great economic value, is susceptible to Aeromonas veronii, a common aquatic pathogen that can cause acute death. Here, we reported the first systematic investigation of circRNAs in yellow catfish, especially those associated with A. veronii infection at different time points. A total of 1205 circRNAs were identified, which were generated from 875 parental genes. After infection, 47 circRNAs exhibited differential expression patterns (named DEcirs). The parental genes of these DEcirs were functionally engaged in immune-related processes. Accordingly, seven DEcirs (novel_circ_000226, 278, 401, 522, 736, 843, and 975) and six corresponding parental genes (ADAMTS13, HAMP1, ANG3, APOA1, FGB, and RALGPS1) associated with immunity were obtained, and their expression was confirmed by RT-qPCR. Moreover, we found that these DEcir-gene pairs likely acted through pathways, such as platelet activation, antimicrobial humoral response, and regulation of Ral protein signal transduction, to influence host immune defenses. Additionally, integrated analysis showed that, of the 7 immune-related DEcirs, three targeted 16 miRNAs, which intertwined into circRNA-miRNA networks. These findings revealed that circRNAs, by targeting genes or miRNAs are highly involved in anti-bacterial responses in yellow catfish. Our study comprehensively illustrates the roles of circRNAs in yellow catfish immune defenses. The identified DEcirs and the circRNA-miRNA network will contribute to the further investigations on the molecular mechanisms underlying yellow catfish immune responses.

Isolation, Characterization, and Pathogenicity of an Aeromonas veronii Strain Causing Disease in Rhinogobio ventralis

Rhinogobio ventralis is a rare fish found in the Yangtze River in China and has significant ecological and economic value. In this study, a bacterial strain (RV-JZ01) was isolated from the livers of diseased R. ventralis. This isolate was identified as Aeromonas veronii based on its morphology, biochemical features and 16S rDNA phylogenetic analysis. The artificial infection of healthy R. ventralis (16 ± 2 cm) with RV-JZ01 resulted in the manifestation of clinical symptoms, in accordance with those of naturally infected fish. The 50% lethal dose (LD50) of RV-JZ01 for R. ventralis was 6.3 × 106 CFU/mL. Histopathological examination revealed various pathological changes in the diseased fish, including intestinal villus swelling and rupture, hepatocyte vacuolization, renal tubular cell nuclear enlargement and pyknosis, and myocardial fiber fracture and atrophy. RV-JZ01 infection significantly reduced the gut flora diversity of R. ventralis, with the relative abundances of Firmicutes and Fusobacteria increasing, and those of the Proteobacteria and Bacteroidetes decreasing. The abundance of Lactobacillus and Streptococcus dramatically increased, and the abundance of Clostridium and Escherichia reduced in the intestinal microbiota of R. ventralis infected with RV-JZ01. Antibiotic sensitivity testing revealed that RV-JZ01 was highly susceptible to 12 antimicrobials, including erythromycin, cefalexin, norfloxacin, furazolidone, sulfonamides, enrofloxacin, doxycycline, piperacillin, florfenicol, gentamicin, and lincomycin. These results contribute to the understanding of pathological alterations in R. ventralis following A. veronii infection, offering valuable data to support the implementation of disease treatment.

Effects of phoxim on antibacterial infection of silver carp

The efficacy of phoxim in treating bacterial sepsis in silver carp is significant, yet its underlying mechanism remains elusive. This study aimed to establish a model of Aeromonas veronii infection in silver carp and subsequently treat the infected fish with 10 μg/L phoxim. Kidney and intestine samples from silver carp were collected for transcriptome analysis and assessment of intestinal microbial composition, with the aim of elucidating the mechanism underlying the efficacy of phoxim in treating bacterial sepsis in silver carp. The results of transcriptome and intestinal microbial composition analysis of silver carp kidney indicated that A. veronii infection could up-regulate the expression of il1β, il6, nos2, ctsl, casp3 et al., which means, signifying that the kidney of silver carp would undergo inflammation, induce apoptosis, and alter the composition of intestinal microorganisms. Phoxim immersion might enhance the energy metabolism of silver carp and change its intestinal microbial composition, potentially elevating the antibacterial infection resistance of silver carp. These findings may contribute to an understanding of how phoxim can effectively treat bacterial sepsis in silver carp.

Therapeutic effects of white poplar (Populus alba) leave extract on hepatorenal, stress, and antioxidant-immune parameters of Oreochromis niloticus challenged with Aeromonas veronii

Herbal plants have gained enormous interest due to their immune, antioxidant, and antibacterial activities. The present study proposed that white poplar (Populus alba) leave extract (WPE) might provide a promising alternative to traditional antibiotics to treat Aeromonas veronii infection in Nile tilapia (Oreochromis niloticus). WPE showed an in vitro antibacterial activity [22 ± 0.45 mm inhibition zone, with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 60 µg/mL] against A. veronii. For the in-vivo study, a factorial (2 × 2) design was used to investigate the therapeutic effects of WPE on the antioxidant/immune status and blood biochemical parameters of Nile tilapia challenged with A. veronii. One-hundred sixty fish (33 ± 1.5 g) were assigned into four experimental groups, each with four replicates (4 glass tanks/group, 40 fish/group, 10 fish/tank) for 10 days. In the first (1st) and 2nd groups, 0 and 1.5 mg/L WPE were applied in tank water, respectively, without fish being challenged. In the 3rd and 4th groups, 0 and 1.5 mg/L WPE were applied in tank water, respectively, with fish intraperitoneal inoculated with 0.2 mL of A. veronii (0.5 × 107 CFU). Aeromonas veronii infection significantly diminished the survivability, hepatic catalase, lysozyme activity, nitric oxide, immunoglobulin M, phagocytic %, total protein, albumin, and globulin. Moreover, a significant rise in the hepatic malondialdehyde, serum hepatorenal function indicators, cortisol, and glucose levels were consequences of A. veronii challenge. Interestingly, the interaction between bacterial challenge and WPE application increased the survivability, antioxidant activity, and immune responses and reduced ALT levels of fish treated with WPE during the bacterial challenge. The serum creatinine, cortisol, and glucose levels were decreased in fish treated with WPE during the infection but still higher than in the non-infected fish either treated or not treated with WPE. In conclusion, WPE (1.5 mg/L) can be used as an antibacterial substance in fish farming to alleviate the detrimental impacts of A. veronii infection by enhancing the antioxidant/immune status of the infected fish. These outcomes could help reduce antibiotic usage in fish farms, which is conducive to the sustainable development of aquaculture.

Pathogenicity of Aeromonas veronii Isolated from Diseased Macrobrachium rosenbergii and Host Immune-Related Gene Expression Profiles.

Aeromonas veronii is widespread in aquatic environments and is responsible for infecting various aquatic animals. In this study, a dominant strain was isolated from the hepatopancreas of diseased Macrobrachium rosenbergii and was named JDM1-1. According to its morphological, physiological, and biochemical characteristics and molecular identification, isolate JDM1-1 was identified as A. veronii. The results of artificial challenge showed isolate JDM1-1 had high pathogenicity to M. rosenbergii with an LD50 value of 8.35 × 105 CFU/mL during the challenge test. Histopathological analysis revealed severe damage in the hepatopancreas and gills of the diseased prawns, characterized by the enlargement of the hepatic tubule lumen and gaps between the tubules as well as clubbing and degeneration observed at the distal end of the gill filament. Eight virulence-related genes, namely aer, ompA, lip, tapA, hlyA, flgA, flgM, and flgN, were screened by PCR assay. In addition, virulence factor detection showed that the JDM1-1 isolate produced lipase, lecithinase, gelatinase, and hemolysin. Furthermore, the mRNA expression profiles of immune-related genes of M. rosenbergii following A. veronii infection, including ALF1, ALF2, Crustin, C-lectin, and Lysozyme, were assessed, and the results revealed a significant upregulation in the hepatopancreas and intestines at different hours post infection. This study demonstrates that A. veronii is a causative agent associated with massive die-offs of M. rosenbergii and contributes valuable insights into the pathogenesis and host defense mechanisms of A. veronii invasion.

Modulating the growth, immune/antioxidant traits, immune-related genes, and resistance to Aeromonas veronii infection in Oreochromis niloticus reared under high stocking densities by dietary Lavandula angustifolia essential oil

Modulating the growth, immune/antioxidant traits, immune-related genes, and resistance to Aeromonas veronii infection in Oreochromis niloticus reared under high stocking densities by dietary Lavandula angustifolia essential oil

Bacteriophage adhering to mucus provide protection against Aeromonas veronii infection in scaleless fish

Yellow catfish (Pelteobagrus fulvidraco) is an economically important freshwater cultured fish in China. As a typical scaleless bony fish, the skin mucus plays a critical role in protecting against water-borne microbes. The major challenges in yellow catfish farming are motile Aeromonas septicemia (MAS) and skin ulcerative syndrome, resulting in significant financial losses. In this study, we isolated and identified Aeromonas veronii ZYAH128 as the pathogen responsible for the mass mortality of yellow catfish. To control this pathogen, we explored the use of phages as an alternative approach. Thirty-three phage strains were identified and evaluated for their ability to lyse A. veronii ZYAH128 in vitro. Thereafter, 11 phages were assessed in controlling the infection of A. veronii in yellow catfish via immersion. The two phages, ZPAV-18 and ZPAV-25 provided outstanding prophylactic rates of 85.7% and 71.4%, therapeutic rates of 85.7% and 85.7%, respectively. Phage was able to sustain in yellow catfish mucus for 7 d in flowing water, and the presence of fish mucus increased the susceptibility of A. veronii to phage infection. Our findings supported the symbiotic relationship where phages inhabit mucosal surfaces and provide external immunity against bacterial infection. Overall, this study provides valuable insights into the potential of phage therapy for combating bacterial infections in scaleless fish.

Expression profiles of four Nile Tilapia innate immune genes during early stages of Aeromonas veronii infection.

During Egypt's hot summer season, Aeromonas veronii infection causes catastrophic mortality on Nile Tilapia Oreochromis niloticus farms. Egypt is ranked first in aquaculture production in Africa, sixth in aquaculture production worldwide, and third in global tilapia production. This study aimed to investigate, at the molecular level, the early innate immune responses of Nile Tilapia to experimental A. veronii infection. The relative gene expression, co-expression clustering, and correlation of four selected immune genes were studied by quantitative real-time polymerase chain reaction in four organs (spleen, liver, gills, and intestine) for up to 72 h after a waterborne A. veronii challenge. The four genes studied were nucleotide-binding oligomerization domain 1 (NOD1), lipopolysaccharide-binding protein (LBP), natural killer-lysin (NKL), and interleukin-1 beta (IL-1β). The four genes showed significant transcriptional upregulation in response to infection. At 72 h postchallenge, the highest NOD1 and IL-1β expression levels were recorded in the spleen, whereas the highest LBP and NKL expression levels were found in the gills. Pairwise distances of the data points and the hierarchical relationship showed that NOD1 clustered with IL-1β, whereas LBP clustered with NKL; both genes within each cluster showed a significant positive expression correlation. Tissue clustering indicated that the responses of only the gill and intestine exhibited a significant positive correlation. The results suggest that NOD1, LBP, NKL, and IL-1β genes play pivotal roles in the early innate immune response of Nile Tilapia to A. veronii infection, and the postinfection expression profile trends of these genes imply tissue-/organ-specific responses and synchronized co-regulation.

Transcriptomic and proteomic insights into the immune response of the intestine to Aeromonas veronii infection in koi carp (Cyprinus carpio var. koi)

Intestinal mucosal immunity serves as one of the primary barriers against pathogens. The immune mechanism involved in fish intestinal defense against bacterial infection still needs further investigation. To delve into the intestinal immune mechanisms of koi carp (Cyprinus carpio var. koi) against Aeromonas veronii infection, RNA-seq and isobaric tags for relative and absolute quantitation (iTRAQ)-coupled LC-MS/MS were employed. After A. veronii infection, 7224 differently expressed genes (DEGs) and 1482 differently expressed proteins (DEPs) were detected in the intestines of koi carp. Further, the integrated analysis of transcriptomic and proteomic data revealed that 471 DEGs were matched with the corresponding DEPs (named associated DEPs/DEGs). Among the 34 immune-related associated DEPs/DEGs, 21 were in the consistent expression tendency, whereas 13 were in the opposite tendency. Moreover, the immune-related associated DEPs/DEGs exhibiting consistent expression trends were predominantly enriched in nine pathways, with five of them being linked to innate immunity: ferroptosis, phagosome, complement and coagulation cascades, MAPK signaling pathway, and NLR signaling pathway. The expression patterns of tested genes detected using quantitative real-time PCR assay were consistent with the findings from RNA-Seq and iTRAQ. A potential offense and defense model between A. veronii and koi carp was established based on insights into the immune-related pathways, DEGs, and DEPs. Overall, our comprehensive transcriptome and proteome analysis allow us to better understand the intestinal mucosal immunity of teleost and the pathogenic mechanism of A. veronii.

A novel formula of herbal extracts regulates growth performance, antioxidant capacity, intestinal microbiota and resistance against Aeromonas veronii in largemouth bass (Micropterus salmoides)

In this study, a novel herbal extracts formula (HE) comprising Scutellaria baicalensis, Taraxacum mongolicum, Biancaea sappan and Pulsatilla chinensis extract with a weight ratio of 3.0: 1.8: 3.0: 1.7, was selected based on bacteriostatic test in vitro. Subsequently, a 30-day feeding trial was conducted to evaluate the effect of dietary HE (0, 0.05, 0.10, 0.50 and 1.00%, respectively) inclusion on the performance of largemouth bass (Micropterus salmoides). The results unveiled that dietary HE 0.10% and HE 0.50% inclusion notably increased the specific growth rate (SGR) and antioxidant enzyme (SOD and GPX) activities in the intestine and liver of fish (p < 0.05). Additionally, a significantly greater height of villi and width of villi were observed in the HE 0.50% and HE 0.10% groups, respectively (p < 0.05). Conversely, histological examination indicated that dietary HE1.00% inclusion led to discernible injury to the intestines, with certain villi displaying breakage and shedding. Hematological parameters including white blood cells (WBC) and red blood cells (RBC) were significantly increased, while the erythrocyte indices including average cellular hemoglobin (MCH), and average cellular hemoglobin concentration (MCHC) remarkably decreased in fish fed HE inclusion compared to the basal diet. The 16S rRNA sequence analysis demonstrated that Cetobacterium, Aeromonas and Plesiomonas were the three dominant species in the intestines regardless of diet. Additionally, the LEfSe analysis revealed that Aeromonas was the most affected taxon, which significantly decreased in the HE 0.10%, HE 0.50% and HE 1.00% groups (p < 0.05), while the Cetobacterium content remarkably increased in HE 0.10% and HE 0.50% groups (p < 0.05). Finally, the highest survival rate of fish infected with Aeromonas veronii HZ012 was observed in the group supplemented with 0.50% HE. Collectively, our study revealed that the supplementation of HE at a proportion of 0.10–0.50% could lead to a promotion of growth performance, maintenance of liver and intestinal health, as well as a protective effect against A. veronii infection in largemouth bass.

Role of Type VI secretion system in pathogenic remodeling of host gut microbiota during Aeromonas veronii infection.

Intestinal microbial disturbance is a direct cause of host disease. The bacterial Type VI secretion system (T6SS) often plays a crucial role in the fitness of pathogenic bacteria by delivering toxic effectors into target cells. However, its impact on the gut microbiota and host pathogenesis is poorly understood. To address this question, we characterized a new T6SS in the pathogenic Aeromonas veronii C4. First, we validated the secretion function of the core machinery of A. veronii C4 T6SS. Second, we found that the pathogenesis and colonization of A. veronii C4 is largely dependent on its T6SS. The effector secretion activity of A. veronii C4 T6SS not only provides an advantage in competition among bacteria in vitro, but also contributes to occupation of an ecological niche in the nutritionally deficient and anaerobic environment of the host intestine. Metagenomic analysis showed that the T6SS directly inhibits or eliminates symbiotic strains from the intestine, resulting in dysregulated gut microbiome homeostasis. In addition, we identified three unknown effectors, Tse1, Tse2, and Tse3, in the T6SS, which contribute to T6SS-mediated bacterial competition and pathogenesis by impairing targeted cell integrity. Our findings highlight that T6SS can remodel the host gut microbiota by intricate interplay between T6SS-mediated bacterial competition and altered host immune responses, which synergistically promote pathogenesis of A. veronii C4. Therefore, this newly characterized T6SS could represent a general interaction mechanism between the host and pathogen, and may offer a potential therapeutic target for controlling bacterial pathogens.