Virulent and Multi-drug-Resistant Edwardsiella tarda Infection in Oscar Fish: Unveiling the Threat of Mass Mortality and AMR Dissemination.

The Oscar fish (Astronotus ocellatus) is among the most commonly domesticated and exported ornamental fish species from Kerala. The ornamental fish industry faces a significant challenge with the emergence of diseases caused by multi-drug-resistant bacteria. In the present study, six isolates were resolved from the diseased Oscar fish showing haemorrhages, necrosis, and loss of pigmentation. After phenotypic and genotypic characterization, the bacteria were identified as Edwardsiella tarda, Klebsiella pneumoniae, Enterococcus faecalis, Escherichia coli, Brevibacillus borstelensis, and Staphylococcus hominis. Experimental challenge studies in healthy Oscar fish showed that E. tarda caused 100% mortality within 240 h with 6.99 × 106 CFU/fish as LD50 and histopathology revealed the typical signs of infection. The pathogen was re-recovered from the moribund fish thereby confirming Koch's postulates. E. tarda was confirmed through the positive amplification of tarda-specific gene and virulence genes viz., etfD and escB were also detected using PCR. Antibiotic susceptibility tests using disc diffusion displayed that the pathogen is multi-drug-resistant towards antibiotics belonging to aminoglycosides, tetracyclines, and quinolones categories with a MAR index of 0.32, which implicated the antibiotic pressure in the farm. Plasmid curing studies showed a paradigm shift in the resistance pattern with MAR index of 0.04, highlighting the resistance genes are plasmid-borne except for the chromosome-borne tetracycline resistance gene (tetA). This study is the first of its kind in detecting mass mortality caused by E. tarda in Oscar fish. Vigilant surveillance and strategic actions are crucial for the precise detection of pathogens and AMR in aquaculture.

Neonatal sepsis with meningitis, ventriculitis and brain abscess caused by Edwardsiella tarda.

A case of neonatal sepsis caused by Edwardsiella tarda, an uncommon pathogen typically associated with aquatic lifeforms, is described. The infant presented in septic shock with seizures and respiratory failure and was found to have meningitis, ventriculitis and a brain abscess requiring drainage. Only a small number of case reports of neonatal E. tarda infection, several with sepsis with poor auditory or neurodevelopmental outcomes or meningitis, have been described in the literature. This case report suggests that E. tarda, while uncommon, can be a cause of serious central nervous system disease in the neonatal population and that an aggressive approach to pursuing and treating complications may lead to improved neurodevelopmental outcomes.

Simultaneous detection of multiple bacterial and viral aquatic pathogens using a fluorogenic loop-mediated isothermal amplification-based dual-sample microfluidic chip.

Rapid and user-friendly diagnostic tests are necessary for early diagnosis and immediate detection of diseases, particularly for on-site screening of pathogenic microorganisms in aquaculture. In this study, we developed a dual-sample microfluidic chip integrated with a real-time fluorogenic loop-mediated isothermal amplification assay (dual-sample on-chip LAMP) to simultaneously detect 10 pathogenic microorganisms, that is Aeromonas hydrophila, Edwardsiella tarda, Vibrio harveyi, V. alginolyticus, V. anguillarum, V. parahaemolyticus, V. vulnificus, infectious hypodermal and haematopoietic necrosis virus, infectious spleen and kidney necrosis virus, and white spot syndrome virus. This on-chip LAMP provided a nearly automated protocol that can analyse two samples simultaneously, and the tests achieved limits of detection (LOD) ranging from 100 to 10-1  pg/µl for genomic DNA of tested bacteria and 10-4 to 10-5  pg/µl for recombinant plasmid DNA of tested viruses, with run times averaging less than 30 min. The coefficient of variation for the time-to-positive value was less than 10%, reflecting a robust reproducibility. The clinical sensitivity and specificity were 93.52% and 85.53%, respectively, compared to conventional microbiological or clinical methods. The on-chip LAMP assay provides an effective dual-sample and multiple pathogen analysis, and thus would be applicable to on-site detection and routine monitoring of multiple pathogens in aquaculture.

Edwardsiella tarda induces enteritis in farmed seahorses (Hippocampus erectus): An experimental model and its evaluation.

Bacterial enteritis is an important deadly threat to farmed seahorses. However, its pathogenesis is obscure because of the paucity of reproducible experimental intestinal inflammation models. Herein, a strain of Edwardsiella tarda YT1 from farmed seahorse Hippocampus erectus was isolated and identified by morphological, phylogenetic, and biochemical analysis, and confirmed as a pathogen of enteritis for the first time by challenge experiment. Two E. tarda concentrations (1 × 105 and 1 × 107 colony forming units [cfu] ml-1) were confirmed suitable for an enteritis model by intraperitoneal injection. To develop and evaluate the experimental model, we challenged seahorses with E. tarda and found that (1) the infection inhibited body length increase, significantly decreased body weight (P < 0.05), and induced typical pathological features including anorexia, anal inflammation, and intestinal fluid retention; (2) 19 external (weight, height, anal inflammation, feeding status, and intestinal fluid retention), histological (goblet and inflammatory cell numbers and thickening of lamina propria and muscularis mucosae), and molecular (hepcidin, liver-expressed antimicrobial peptide, lysozyme, piscidin, interleukin [IL]-1ß, IL-1ß receptor, IL-2, IL-10, interferon1, tumor necrosis factor [TNF]-α, and toll-like receptor 5 [TLR5]) indicators were suitable for model evaluation, as they could sensitively respond and varied similarly throughout the experiment, indicating the high sensitivity of seahorses against pathogen invasion; (3) TLR5 may play an essential role in triggering host immune responses during E. tarda-induced chronic enteritis, and (4) the evaluating system could reflect the pattern and intensity of disease progression. Thus, we developed an experimental model and an evaluating system of bacterial enteritis in farmed seahorses, helping us to reveal the pathogenesis of bacterial enteritis, identify potential therapeutic drugs, and search suitable genetic markers for seahorse molecular breeding.

A case of necrotizing fasciitis following Edwardsiella tarda septicemia with gastroenteritis.

Edwardsiella tarda is an uncommon pathogen that causes gastroenteritis in humans and is found in the aquatic environment. In rare cases, it also causes fatal infections, including sepsis and necrotizing fasciitis. However, it remains unknown whether E. tarda gastroenteritis could lead to these lethal diseases via hematogenous spread. Here we have reported a previously healthy 64-year-old woman with necrotizing fasciitis consecutively caused by E. tarda septicemia with gastroenteritis. The patient was transferred to the emergency department due to disturbance of consciousness and hypotension after suffering from diarrhea for a month. As whole-body computed tomography (CT) revealed an edematous change in the small intestine, septic shock following gastroenteritis was suspected, and the patient was immediately started on empiric antibiotic therapy and provided critical care. Her general physical conditions gradually began improving, but, on day 7, rapidly appearing blisters on both the lower limbs were noted, and she was accordingly examined again by conducting a CT scan. Based on the results, she was diagnosed with necrotizing fasciitis in both lower extremities, and surgical debridement was rapidly performed. Microbiological analysis of the specimens revealed E. tarda bacteremia, which suggested that E. tarda caused a series of infections in this patient. Finally, she fully recovered and was discharged within 3 months. Cumulatively, we proposed that gastroenteritis by E. tarda could directly result in fatal infections through the blood stream.

Catfish Bite Case Report.

Although catfish are found worldwide and commonly consumed in the southern United States, fatal infections from catfish are rare. Edwardsiella tarda is a bacterium known to cause gastrointestinal distress most commonly, but extraintestinal infections are a rarely considered danger for those acquiring, preparing, and consuming aquatic animals. Susceptible to all gram-negative active antibiotics, it is easily treated except in immunocompromised hosts, such as those with malignancy, diabetes, and hepatic dysfunction.

De novo whole transcriptome profiling of Edwardsiella tarda isolated from infected fish (Labeo catla).

Edwardsiella tarda belongs to the genera of Gram negative bacterium mainly associated with edwardsiellosis, the most commonly found infectious fish disease throughout the globe. E. tarda is also a widespread pathogen which cause infections such as cellulitis or gas gangrene and generalized infections in humans. To control the escalating infection of E. trada on various species, it is essential to decoded the mysterious mechanism behind the bacterial infection at transcript level. In this present study, we carry out a de novo E. tarda Whole transcriptome sequencing, isolated from infected fish intestine using SOLiD sequencing platform. RNA-Seq data analysis was performed using various bioinformatics pipelines. Protein-protein interaction study for pathway enrichment and gene ontology study were executed for further investigation. Assembly statistics for E. tarda dataset showed that the number of transcript contigs was 9657 out of which 6749 were GO annotated whereas 1528 were not assigned any GO terms. GO analysis showed that the expressed genes were enhanced with molecular function, cellular component and biological process. A KEGG enrichment study showed that pathway's that are directly linked with immune diseases like Rheumatoid arthritis (0.2%), Tuberculosis (0.3%) Endocytosis (0.6%) was considerably enriched. Protein-protein interaction study showed that most of the expressed proteins were involved in metabolic pathways, flagellar assembly, Propanoate metabolism, Microbial metabolism in diverse environments, Butanoate metabolism and Carbon. The present study provides novel E. tarda transcriptome sequence data, allowing us to identify biologically significant genes and their functional relationship with fish diseases, and will be useful in recognize the reliable therapeutic targets in near feature.

Graphene-Based Steganographically Aptasensing System for Information Computing, Encryption and Hiding, Fluorescence Sensing and in Vivo Imaging of Fish Pathogens.

Inspired by information processing and communication of life based on complex molecular interactions, some artificial (bio)chemical systems have been developed for applications in molecular information processing or chemo/biosensing and imaging. However, little attention has been paid to simultaneously and comprehensively utilize the information computing, encoding, and molecular recognition capabilities of molecular-level systems (such as DNA-based systems) for multifunctional applications. Herein, a graphene-based steganographically aptasensing system was constructed for multifunctional application, which relies on specific molecular recognition and information encoding abilities of DNA aptamers ( Aeromonas hydrophila and Edwardsiella tarda-binding aptamers as models) and the selective adsorption and fluorescence quenching capacities of graphene oxide (GO). Although graphene-DNA systems have been widely used in biosensors and diagnostics, our proposed graphene-based aptasensing system can not only be utilized for fluorescence sensing and in vivo imaging of fish pathogens ( A. hydrophila and E. tarda), but can also function as a molecular-level logic computing system where the combination of matters (specific molecules or materials) as inputs produces the resulting product (matter level) or fluorescence (energy level) changes as two outputs. More importantly and interestingly, our graphene-based steganographically aptasensing system can also serve as a generally doubly cryptographic and steganographic system for sending different secret messages by using pathogen-binding DNA aptamers as information carriers, GO as a cover, and a pair of keys, that is, target pathogen as a public key, the encryption key used to encode or decode a message in DNA as a private key. Our study not only provides a novel nanobiosensing assay for rapid and effective sensing and in vivo imaging of fish pathogens, but also demonstrates a prototype of (bio)molecular steganography as an important and interesting extension direction of molecular information technology, which is helpful in probably promoting the development of multifunctional molecular-level devices or machines.

Systemic Edwardsiella tarda infection in a Western African lungfish (Protopterus annectens) with cytologic observation of heterophil projections.

This report describes a case of systemic bacterial infection caused by Edwardsiella tarda in a Western African lungfish (Protopterus annectens) exposed to poor environmental and husbandry conditions. The fish presented with a large, external ulcerative lesion and died 2 weeks after developing anorexia. Histological evaluation revealed multifocal areas of necrosis and heterophilic and histiocytic inflammation throughout multiple tissues. Gram stain identified small numbers of intra- and extracellular monomorphic Gram-negative 1 to 2 µm rod-shaped bacilli. Cytology of lung granuloma, kidney and testes imprints identified heterophilic inflammation with phagocytosis of small monomorphic bacilli and some heterophils exhibiting cytoplasmic projections indicative of heterophil extracellular traps (HETs). Initial phenotypic analysis of isolates from coelomic fluid cultures identified E. tarda. Subsequent molecular analysis of spleen, liver and intestine DNA using an E. tarda-specific endpoint PCR assay targeting the bacterial fimbrial subunit yielded a 115 bp band. Sequencing and BLASTN search revealed the sequence was identical (76/76) to E. tarda strain FL95-01 (GenBank acc. CP011359) and displayed 93% sequence identity (66/71) to Edwardsiella hoshinae strain ATCC 35051 (GenBank acc. CP011359). This is the first report of systemic edwardsiellosis in a lungfish with concurrent cytologically identified structures suggestive of HETs.

Mycotic aneurysm caused by Edwardsiella tarda successfully treated with stenting and suppressive antibiotic therapy: a case report and systematic review.

BACKGROUND: Mycotic aneurysm is an uncommon disease which could be fatal without appropriate treatment. Although standard therapy for mycotic aneurysms consists of resection of the infected aorta and in situ graft replacement, some treat with endovascular stent-grafting because patients may not tolerate graft replacement due to underlying diseases. There are 6 more reported cases of mycotic aneurysm caused by Edwardsiella tarda. With the exception of our case, all underwent resection and debridement of the infected aorta or vascular prosthesis. Herein we report the first case ever of mycotic aneurysm caused by E. tarda, successfully treated with stenting and suppressive antibiotic therapy without resection of the infected aorta. CASE PRESENTATION: A 65-year-old Japanese woman with cirrhosis and hepatocellular carcinoma complained of fatigue. Her work up revealed a ruptured aneurysm of the descending aorta. She went through endovascular stent-graft placement. Edwardsiella tarda grew from blood cultures, which led to the diagnosis of mycotic aneurysm. Edwardsiella tarda is a Gram negative bacillus which rarely causes infections in humans. In the case of bacteremia, its mortality is reported to be very high and all reported cases with mycotic aneurysm caused by E. tarda ended up with resection of the infected aorta. CONCLUSION: Our case shows that in the case of mycotic aneurysm caused by E. tarda, endovascular stent-graft placement could be an alternative to in situ graft replacement.

First report of the occurrence and whole-genome characterization of Edwardsiella tarda in the false killer whale (Pseudorca crassidens).

Although several Edwardsiella tarda infections have been reported, its pathogenic role in marine mammals has not been investigated at the genome level. We investigated the genome of E. tarda strain KC-Pc-HB1, isolated from the false killer whale (Pseudorca crassidens) found bycaught in South Korea. The obtained genome was similar to that of human pathogenic E. tarda strains, but distinct from other Edwardsiella species. Although type III and VI secretion systems, which are essential for the virulence of other Edwardsiella species, were absent, several virulence-related genes involved in the pathogenesis of E. tarda were found in the genome. These results provide important insights into the E. tarda infecting marine mammals and give valuable information on potential virulence factors in this pathogen.

Edwardsiella tarda outbreak affecting fishes and aquatic birds in Brazil.

BACKGROUND: Edwardsiella tarda infections are frequent causes of severe outbreaks in the fish farming industry besides representing possible zoonotic risks. However, naturally occurring outbreaks that affect various species besides fishes are seldom described. AIM: To report an outbreak of acute mortality caused by E. tarda affecting multiple species that inhabited a natural pond in the state of São Paulo, Brazil. MATERIALS AND METHODS: Three adult tilapias, three Mallard ducks and one Snow egret were necropsied and subjected to further microbiological tests. Gross and microscopic lesions were documented. The antibiotic susceptibility and phylogenetic similarities among fish and avian strains were also determined. The E. tarda species was confirmed through MALDI-TOF, partial sodB sequencing and phylogenetic analysis. RESULTS: Macroscopical findings between the three species included intestinal dilatation, mucosal hyperaemia and mucous to liquid contents. Common histopathology findings included acute enteritis, increased number of intraepithelial lymphocytes with bacteria adhered to the intestinal epithelium and lymphoid depletion in the spleen. E. tarda was isolated from several organs from all affected species. The phylogeny employing amplified fragment length polymorphism (AFLP) of eleven strains revealed high similarity (>90%) among the isolates regardless of the affected species or sampled organs. Ten isolates of E. tarda showed susceptibility to all tested antibiotics. CONCLUSIONS: E. tarda was identified as the cause of death of the species examined. Further studies would be necessary to determine the virulence of these strains and the possible risks regarding public health.

Maternal peripartum septic shock caused by intrauterine infection with Edwardsiella tarda: A case report and review of the literature.

Edwardsiella tarda (E. tarda) is a rare pathogen in humans, especially during the peripartum period. Only a few cases of fatal neonatal infection with E. tarda have been reported. Herein, we describe a case of maternal septicemia caused by E. tarda following peripartum chorioamnionitis. The mother developed septic shock, disseminated intravascular coagulation and a post-cesarean wound hematoma with abscess. Her condition improved with multidisciplinary therapy including blood transfusion, antimicrobial agents, recombinant thrombomodulin and surgical debridement. E. tarda was isolated from the maternal blood, cesarean wound and neonatal skin, pharynx and gastric fluid. This case demonstrates that peripartum infection with E. tarda is a rare but life-threatening condition, not only for the neonate but also for the mother.

Edwardsiella tarda Bacteremia with Psoas and Epidural Abscess as a Food-borne Infection: A Case Report and Literature Review.

Edwardsiella tarda is commonly isolated from aquatic environments and a variety of animals. We present the first case of E. tarda bacteremia with psoas and epidural abscess. The patient was a 65-year-old woman with recurrent gastric cancer who had frequently consumed raw fish and grilled eel. She was successfully treated with antimicrobials and surgery. We also review reports published in English regarding E. tarda bacteremia in Japan and the experience at our hospital. On the basis of this review, we conclude that the major underlying disease leading to E. tarda bacteremia is malignancy and that the gastrointestinal tract is the most commonly affected organ. The overall mortality rate due to E. tarda bacteremia in our review was 38.1% (8/21). Although E. tarda bacteremia is rare, clinicians should be aware of this fatal food-borne infection.

Comparative Phenotypic and Genotypic Analysis of Edwardsiella Isolates from Different Hosts and Geographic Origins, with Emphasis on Isolates Formerly Classified as E. tarda, and Evaluation of Diagnostic Methods.

Edwardsiella spp. are responsible for significant losses in important wild and cultured fish species worldwide. Recent phylogenomic investigations have determined that bacteria historically classified as Edwardsiella tarda actually represent three genetically distinct yet phenotypically ambiguous taxa with various degrees of pathogenicity in different hosts. Previous recognition of these taxa was hampered by the lack of a distinguishing phenotypic character. Commercial test panel configurations are relatively constant over time, and as new species are defined, appropriate discriminatory tests may not be present in current test panel arrangements. While phenobiochemical tests fail to discriminate between these taxa, data presented here revealed discriminatory peaks for each Edwardsiella species using matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) methodology, suggesting that MALDI-TOF can offer rapid, reliable identification in line with current systematic classifications. Furthermore, a multiplex PCR assay was validated for rapid molecular differentiation of the Edwardsiella spp. affecting fish. Moreover, the limitations of relying on partial 16S rRNA for discrimination of Edwardsiella spp. and advantages of employing alternative single-copy genes gyrB and sodB for molecular identification and classification of Edwardsiella were demonstrated. Last, sodB sequencing confirmed that isolates previously defined as typical motile fish-pathogenic E. tarda are synonymous with Edwardsiella piscicida, while atypical nonmotile fish-pathogenic E. tarda isolates are equivalent to Edwardsiella anguillarum Fish-nonpathogenic E. tarda isolates are consistent with E. tarda as it is currently defined. These analyses help deconvolute the scientific literature regarding these organisms and provide baseline information to better facilitate proper taxonomic assignment and minimize erroneous identifications of Edwardsiella isolates in clinical and research settings.

Identification and validation of sRNAs in Edwardsiella tarda S08.

Bacterial small non-coding RNAs (sRNAs) are known as novel regulators involved in virulence, stress responsibility, and so on. Recently, a lot of new researches have highlighted the critical roles of sRNAs in fine-tune gene regulation in both prokaryotes and eukaryotes. Edwardsiella tarda (E. tarda) is a gram-negative, intracellular pathogen that causes edwardsiellosis in fish. Thus far, no sRNA has been reported in E. tarda. The present study represents the first attempt to identify sRNAs in E. tarda S08. Ten sRNAs were validated by RNA sequencing and quantitative PCR (qPCR). ET_sRNA_1 and ET_sRNA_2 were homolous to tmRNA and GcvB, respectively. However, the other candidate sRNAs have not been reported till now. The cellular abundance of 10 validated sRNA was detected by qPCR at different growth phases to monitor their biosynthesis. Nine candidate sRNAs were expressed in the late-stage of exponential growth and stationary stages of growth (36~60 h). And the expression of the nine sRNAs was growth phase-dependent. But ET_sRNA_10 was almost expressed all the time and reached the highest peak at 48 h. Their targets were predicted by TargetRNA2 and each sRNA target contains some genes that directly or indirectly relate to virulence. These results preliminary showed that sRNAs probably play a regulatory role of virulence in E. tarda.

The development of cellular immune defence in marine medaka Oryzias melastigma.

Environmentally induced alterations of the immune system during sensitive developmental stages may manifest as abnormalities in immune organ configuration and/or immune cell differentiation. These not only render the early life stages more vulnerable to pathogens, but may also affect the adult immune competence. Knowledge of these sensitive periods in fish would provide an important prognostic/diagnostic tool for aquatic risk assessment of immunotoxicants. The marine medaka Oryzias melastigma is an emerging seawater fish model for immunotoxicology. Here, the presence and onset of four potentially sensitive periods during the development of innate and adaptive cellular immune defence were revealed in O. melastigma: 1.) initiation of phagocyte differentiation, 2.) migration and expansion of lymphoid progenitor cells, 3.) colonization of immune organs through lymphocyte progenitors and 4.) establishment of immune competence in the thymus. By using an established bacterial resistance assay for O. melastigma, larval immune competence (from newly hatched 1dph to 14dph) was found concomitantly increased with advanced thymus development and the presence of mature T-lymphocytes. A comparison between the marine O. melastigma and the freshwater counterpart Oryzias latipes disclosed a disparity in the T-lymphocyte maturation pattern, resulting in differences in the length of T-lymphocyte maturation. The results shed light on a potential difference between seawater and freshwater medaka in their sensitivity to environmental immunotoxicants. Further, medaka immune system development was compared and contrasted to economically important fish. The present study has provided a strong scientific basis for advanced investigation of critical windows for immune system development in fish.

Identification of genes associated with the penetration activity of the human type of Edwardsiella tarda EdwGII through human colon epithelial cell monolayers.

Edwardsiella tarda is a Gram-negative pathogen with a broad host range including fish and humans. E. tarda causes gastrointestinal and extraintestinal infections in humans. In present study, the penetration activities of 22 strains of E. tarda, including 10 human isolates and 12 diseased fish isolates, through Caco-2 cell monolayers were evaluated. All the human isolates exhibited penetration activity in contrast to the fish isolates, which did not. In order to identify genes responsible for penetration activity, we screened transposon (Tn) insertion mutants for reduced penetration activity. Two Tn insertion mutants showed markedly reduced penetration activity, and we identified the wecC and fliF genes as Tn insertion sites. The wecC and fliF genes encode UDP-N-acetyl-d-mannosamine dehydrogenase, which is involved in synthesis of enterobacterial common antigen and flagellar basal body M-ring protein, respectively. Motility activity, including swarming and swimming, by the wecC mutant was weaker than that by the wild-type strain, while the fliF mutant was immotile. These results indicated that the swarming and swimming abilities mediated by the wecC and fliF genes appeared to be essential for penetration activity of E. tarda through Caco-2 cell monolayers. We also demonstrated that it was possible to group E. tarda strains into two types of human isolates and diseased fish isolates based on distribution of the wecC gene, type III and type VI secretion system genes. PCR detection of the wecC gene may represent a useful method for detecting the human type of E. tarda, which may have the ability to cause human infection.