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1.
Since 2012, low‐to‐moderate mortality associated with an Erysipelothrix sp. bacterium has been reported in ornamental fish. Histological findings have included facial cellulitis, necrotizing dermatitis and myositis, and disseminated coelomitis with abundant intralesional Gram‐positive bacterial colonies. Sixteen Erysipelothrix sp. isolates identified phenotypically as E. rhusiopathiae were recovered from diseased cyprinid and characid fish. Similar clinical and histological changes were also observed in zebrafish, Danio rerio, challenged by intracoelomic injection. The Erysipelothrix sp. isolates from ornamental fish were compared phenotypically and genetically to E. rhusiopathiae and E. tonsillarum isolates recovered from aquatic and terrestrial animals from multiple facilities. Results demonstrated that isolates from diseased fish were largely clonal and divergent from E. rhusiopathiae and E. tonsillarum isolates from normal fish skin, marine mammals and terrestrial animals. All ornamental fish isolates were PCR positive for spaC, with marked genetic divergence (<92% similarity at gyrB, <60% similarity by rep‐PCR) between the ornamental fish isolates and other Erysipelothrix spp. isolates. This study supports previous work citing the genetic variability of Erysipelothrix spp. spa types and suggests isolates from diseased ornamental fish may represent a genetically distinct species.  相似文献   

2.
In response to a mortality event, seven Pangasius catfish (Pangasianodon hypophthalmus) were submitted to the University of the West Indies, School of Veterinary Medicine, Trinidad and Tobago, for diagnostic evaluation. These fish were part of a consignment that arrived from Kolkata two weeks earlier. Fish presented with perianal haemorrhage and blister‐like swellings on the skin which ruptured to leave ulcers. Edwardsiella ictaluri was consistently recovered from the brain and skin. Repetitive sequence‐mediated PCR analysis revealed genetic fingerprints consistent with E. ictaluri isolates from farm‐raised channel catfish in Mississippi, USA. Plasmid analysis of the case isolates identified two unique plasmids that differ slightly in conformation and content from the pEI1 and pEI2 plasmids described for E. ictaluri from other fish hosts. The case isolates were also PCR negative for several E. ictaluri virulence factors. The biological implications of these genetic differences are unclear and warrant further study. This is the first report and documentation of E. ictaluri infection in Trinidad and Tobago, suggesting the pathogen may have been introduced concurrently with the importation of fish. This report emphasizes the importance of adequate health screenings of imported lots to minimize the threat of introducing E. ictaluri to non‐endemic areas.  相似文献   

3.
A molecular epidemiology study was conducted on 90 Edwardsiella ictaluri isolates recovered from diseased farmed freshwater catfish, Pangasianodon hypophthalmus, cultured in the Mekong Delta, Vietnam. Thirteen isolates of E. ictaluri derived from diseased channel catfish, Ictalurus punctatus, cultured in the USA were included for comparison. All the E. ictaluri isolates tested were found to be biochemically indistinguishable. A repetitive (rep)‐PCR using the single (GTG)5 primer was shown to possess limited discriminatory power, yielding two similar DNA profiles categorized as (GTG)5‐PCR group 1 or 2 among the Vietnam isolates and (GTG)5‐PCR group 1 within the USA isolates. Macrorestriction analysis identified 14 and 22 unique pulsotypes by XbaI and SpeI, respectively, among a subset of 59 E. ictaluri isolates. Numerical analysis of the combined macrorestriction profiles revealed three main groups: a distinct cluster formed exclusively of the USA isolates, and a major and minor cluster with outliers contained the Vietnam isolates. Antibiotic susceptibility and plasmid profiling supported the existence of the three groups. The results indicate that macrorestriction analysis may be regarded as a suitable typing method among the E. ictaluri species of limited intraspecific diversity. Furthermore, the findings suggest that E. ictaluri originating from Vietnam may constitute a distinct genetic group.  相似文献   

4.
Edwardsiella ictaluri infects several fish species and protection of the all the susceptible fish hosts from the pathogen using a monovalent vaccine is impossible because the species is composed of host-based genotypes that are genetic, serological and antigenic heterogenous. Here, immunoinformatic approach was employed to design a cross-immunogenic chimeric EiCh protein containing multi-epitopes. The chimeric EiCh protein is composed of 11 B-cell epitopes and 7 major histocompatibility complex class II epitopes identified from E. ictaluri immunogenic proteins previously reported. The 49.32 kDa recombinant EiCh protein was expressed in vitro in Escherichia coli BL-21 (DE3) after which inclusion bodies were successfully solubilized and refolded. Ab initio protein modelling revealed secondary and tertiary structures. Secondary structure was confirmed by circular dichroism spectroscopy. Antigenicity of the chimeric EiCh protein was exhibited by strong reactivity with serum from striped catfish and Nile tilapia experimentally infected with E. ictaluri. Furthermore, immunogenicity of the chimeric EiCh protein was investigated in vivo in Nile tilapia juveniles and it was found that the protein could strongly induce production of specific antibodies conferring agglutination activity and partially protected Nile tilapia juveniles with a relative survival percentage (RPS) of 42%. This study explored immunoinformatics as reverse vaccinology approach in vaccine design for aquaculture to manage E. ictaluri infections.  相似文献   

5.
Mucins are large glycoproteins that cover epithelial surfaces of the body and play important roles in prevention of inflammatory and various infectious diseases. In this study, five membrane‐bound and seven secreted mucin genes in the channel catfish were identified. All these identified mucin genes possess at least one PTS, von Willebrand D (VWD) or SEA domains. The expression of the 12 mucin genes in channel catfish was first studied with infection of Edwardsiella ictaluri and Flavobacterium columnare. Expression difference in MUC13a, MUC13, MUC2 and MUC5b was found in the intestine after E. ictaluri infection. Eight mucin gene expressions (except MUC3a, MUC2, MUC4 and MUC5f) were up‐regulated at 4 hr and down‐regulated after 24 hr in the gill with F. columnare infection. Expression level of MUC2 gene was up‐regulated in the intestine with E. ictaluri infection without no significant change in the gill under the F. columnare infection, which indicate that MUC2 is tissue‐specific gene expression and has different immune respond to two bacterial challenge. Taken together, the study showed mucin from the gill by F. columnare challenge induced an obvious response than mucin from the intestine with E. ictaluri infection.  相似文献   

6.
This is the first study to isolate, identify and characterize Streptococcus iniae as the causative disease agent in two tilapia (Oreochromis aureus) populations. The populations were geographically isolated, of distinct origins, and did not share water sources. Affected fish showed various external (e.g., exophthalmia and cachexia, among others) and internal (e.g., granulomatous septicaemia and interstitial nephritis, among others) signs. All internal organ samples produced pure cultures, two of which (one from each farm, termed S‐1 and S‐2) were subjected to biochemical, PCR and 16S rRNA sequencing (99.5% similarity) analyses, confirming S. iniae identification. The two isolates presented genetic homogeneity regardless of technique (i.e., RAPD, REP‐PCR and ERIC‐PCR analyses). Pathogenic potentials were assessed through intraperitoneal injection challenges in rainbow trout (Oncorhynchus mykiss) and zebrafish (Danio rerio). Rainbow trout mortalities were respectively 40% and 70% at 104 and 106 CFU per fish with the S‐1 isolate, while 100% mortality rates were recorded in zebrafish at 102 and 104 CFU per fish with the S‐2 isolate. The obtained data clearly indicate a relationship between intensified aquaculture activities in Mexico and new disease appearances. Future studies should establish clinical significances for the tilapia industry.  相似文献   

7.
Enteric septicaemia of catfish (ESC) caused by Edwardsiella ictaluri is becoming an increasing problem in aquaculture and has been reported worldwide in a variety of fish species. This study reports ESC in hybrid catfish, Clarias macrocephalus (Günther) × Clarias gariepinus (Burchell), cultured in southern Thailand. The bacteria were identified as E. ictaluri by conventional and rapid identification systems, as well as by genetic and phylogenetic characterization. Analysis of 16S rRNA indicated 100% homology to the 16S rRNA sequence of several E. ictaluri strains in GenBank. Plasmid profiles demonstrated 4.0‐ and 5.6‐kb plasmids, compared with the 4.8‐ and 5.6‐kb plasmids in the US isolates, and representative genes of three of the four known pathogenicity islands of US isolates were present. Serologically, lipopolysaccharide (LPS) purified from the Thai isolates was not recognized by a monoclonal antibody against the LPS of US isolates. Fish experimentally infected with E. ictaluri showed 23–100% mortality within 14 days with a 168‐h LD50 of 6.92 × 107 CFU mL?1 by immersion and a 96‐h LD50 of 1.58 × 106 CFU fish?1 by intraperitoneal injection. Examination of tissue sections obtained from both naturally and experimentally infected fish indicated that infection of hybrid catfish with E. ictaluri produced lesions in several organs including liver, kidney, spleen, heart and brain. Histopathology findings included cellular necrosis, focal haemorrhage, infiltration of lymphocytes and multifocal granulomatous inflammation in the infected organs.  相似文献   

8.
Aeromonas hydrophila is a pathogen infecting farmed hybrid catfish, Clarias macrocephalus (Günther, 1864) × Clarias gariepinus (Burchell, 1822) which incurs substantial economic losses in Thailand. The study aimed at a genetic tracking of A. hydrophila infection and the in vitro assessment of the efficacy of antibiotics against its virulent strains. Five clinical strains from catfishes and Nile tilapia were employed. They were 3‐passage re‐isolated through healthy hybrid catfish and the cytolytic enterotoxin gene (AHCYTOEN) of individuals was traced. Each of the re‐isolates at a dose of ~6.67 × 105 CFU/g was intraperitoneally injected into ~15 g‐healthy hybrid catfish and their pathogenicity were observed for 7 days. It was found that AHCYTOEN was carried over whereas typical signs of motile aeromonas septicaemia were found in the specimens. The bacterial strains of Nile tilapia origin did not induce mortality but those of catfish origins (80%–100% rate of mortality). The strains were susceptible to the tetracycline antibiotics, and oxytetracycline produced MIC50 and MBC as low as 0.007–0.031 μg/ml and 1–8 μg/ml respectively. As oxytetracycline specifically inhibited pathogenic A. hydrophila in vitro, it is recommended that an appropriate dosage regimen of the drug should be established.  相似文献   

9.
Yellow catfish Pelteobagrus fulvidraco (Richardson) is a commercially important fish generally distributed in Southeast Asian countries. The well‐known aetiological agent of enteric septicaemia of catfish, Edwardsiella ictaluri, was isolated from diseased yellow catfish P. fulvidraco (Richardson) reared at two commercial fisheries in China. The economic losses due to the high mortalities (about 50%) caused by this bacterium have been increasing annually. The affected fish presented two different, typical symptoms: pale gills, slight exophthalmia and a ‘hole in the head’, and haemorrhage on the opercula, in the skin under the jaw, creating a ‘hole under the jaw’. These diseases were found frequently in cultured yellow catfish throughout China. The isolates from both outbreaks were all Gram negative, facultatively anaerobic and short rod. Morphological and biochemical tests and phylogenetic analysis based on the 16S rDNA sequences all strongly indicated that these yellow catfish isolates were highly identical to the known E. ictaluri. In addition, the isolates possessed the typical plasmid profile of E. ictaluri. Experimental infection assays were conducted and pathogenicity (by an intraperitoneal injection) was demonstrated in yellow catfish and channel catfish Ictalurus punctatus. The results showed that yellow catfish isolates were quite conservative phenotypically and genetically, and were able to cause two different, typical symptoms in this fish under unknown conditions and mechanism.  相似文献   

10.
The bacterium Edwardsiella ictaluri is considered to be one of the most significant pathogens of farmed catfish in the United States of America and has also caused mortalities in farmed and wild fishes in many other parts of the world. E. ictaluri is not believed to be present in wild fish populations in Australia, although it has previously been detected in imported ornamental fishes held in quarantine facilities. In an attempt to confirm freedom from the bacterium in Australian native fishes, we undertook a risk‐based survey of wild catfishes from 15 sites across northern Australia. E. ictaluri was detected by selective culturing, followed by DNA testing, in Wet Tropics tandan (Tandanus tropicanus) from the Tully River, at a prevalence of 0.40 (95% CI 0.21–0.61). The bacterium was not found in fishes sampled from any of the other 14 sites. This is the first report of E. ictaluri in wild fishes in Australia.  相似文献   

11.
Eight tetracycline resistant Edwardsiella ictaluri isolates obtained from diseased freshwater catfish (Pangasianodon hypophthalmus) in Vietnam, and showing different resistance phenotypes to other antimicrobial agents, were studied. The tet genes were determined using PCR. Conjugation experiments were performed to assess transferability of the tetracycline resistance determinant and the size and incompatibility group (Inc) of each tet-carrying plasmid were determined. PCR and sequencing were used for characterization of the co-transferred resistance genes. A tetA gene was demonstrated in the E. ictaluri isolates and for all of them, Escherichia coli transconjugants were obtained. All transconjugants contained high-molecular weight tetA-carrying plasmids (~ 140 kb) belonging to the incK group, as was shown with the PCR-based replicon typing method. The strA–strB, dhfr1 and sul 2 genes were detected on the tetA-carrying plasmids of the transconjugants showing resistance to streptomycin, trimethoprim and sulfonamides, respectively. The dhfr1 gene was found to be located in a class 1 integron as determined by PCR and sequencing. Interestingly, the 3′ CS region of class 1 integrons was not detected by PCR. This study shows the presence of incK plasmid-mediated tetracycline resistance among E. ictaluri isolates from diseased freshwater catfish in Vietnam.  相似文献   

12.
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13.
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14.
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15.
The genus Edwardsiella is one of the major causes of fish diseases globally. Herein, we examined 37 isolates from ten different fish species from India, South Korea and Taiwan to gain insight into their phenotypic and genotypic properties, of which 30 were characterized as E. tarda with phenotypic homology estimated at 85.71% based on API‐20E biochemical tests. Genotyping using 16S rRNA put all isolates together with E. anguillarum, E. hoshinae, E. tarda, E. piscicida and E. ictaluri reference strains in a monophyletic group. In contrast, the gyrB phylogenetic tree clearly separated E. ictaluri, E. tarda and E. hoshinae reference strains from our isolates and put our isolates into two groups with group I being homologous with the E. anguillarum reference strain while group II was homologous with the E. piscicida reference strain. Hence, our findings point to E. piscicida and E. anguillarum as species infecting different fish species in Asia. Homology of the ompW protein suggested that strains with broad protective coverage could be identified as vaccine candidates. This study underscores the importance of combining genotyping with phenotyping for valid species classification. In addition, it accentuates the importance of phylogenetic comparison of bacterial antigens for identification of potential vaccine candidates.  相似文献   

16.
A field study to assess the efficacy of florfenicol (FFC) against enteric septicemia of catfish (ESC) was conducted with pond‐reared channel catfish fingerlings held in 0.1‐acre earthen ponds. Fish were challenged with Edwardsiella ictaluri in a natural pond outbreak or by cohabitation with E. ictaluri‐infected fish held in netpens. Fourteen ponds were assigned in equal number to two treatment groups, that is, either treated (with 10 mg FFC/kg body weight in medicated feed) or not treated (control) for 10 consecutive d. The threshold for enrollment into the study was 0.3% cumulative mortality attributed to ESC. Treatment was initiated on different dates for each pond because each pond was enrolled when 33 fish/pond were diagnosed with ESC based on clinical signs, lesions, or positive cultures. Mortality was monitored during the 10‐d treatment period and during a 14‐d posttreatment observation period. At the end of the 14‐d posttreatment observation period, all fish were euthanized, and 20 fish from each pond were examined by gross necropsy and evaluated for the presence of E. ictaluri by bacterial culture. The odds of a mortality in the control group were 2.20 times the odds of a mortality in the FFC‐treated group. Significantly fewer (P≤ 0.05) FFC‐medicated catfish died in comparison to unmedicated catfish. The minimum inhibitory concentration of FFC for this strain of E. ictaluri was 0.25 μg/mL in all fish that were assayed. The mean zone of inhibition (Kirby Bauer) was 36.8 mm from E. ictaluri isolates of test fish. There were no FFC treatment‐related lesions seen on gross pathology. FFC was efficacious and safe for control of mortality from E. ictaluri infection in catfish.  相似文献   

17.
Streptococcus dysgalactiae is an emerging fish pathogen that is responsible for outbreaks of disease on fish farms around the world. Recently, this bacterium was associated with an outbreak at a Nile tilapia, Oreochromis niloticus (L.), farm in Brazil. The aim of this study was to evaluate the genetic diversity, best genotyping method and aspects of molecular epidemiology of S. dysgalactiae infections in Nile tilapia farms in Brazil. Twenty‐one isolates from four farms located in different Brazilian states were characterized genetically using pulsed‐field gel electrophoresis (PFGE), ERIC‐PCR, REP‐PCR and sodA gene sequencing. The discriminatory power of the different typing methods was compared using Simpson's index of diversity. Identical sodA gene sequences were obtained from all isolates, and ERIC‐PCR and REP‐PCR were unable to discriminate among the isolates. PFGE typing detected three different genetic patterns between the 21 strains evaluated; thus, it was the best genotyping method for use with this pathogen. The strains from Ceará State were genetically divergent from those from Alagoas State. The S. dysgalactiae isolates analysed in this study constituted a genetically diverse population with a clear association between geographical origin and genotype.  相似文献   

18.
A bacterial infectivity challenge model of Edwardsiella ictaluri in striped catfish was developed. All experiments were conducted using a bacterial isolate of E. ictaluri that had been recovered during a natural outbreak of bacillary necrosis of Pangasianodon (BNP) in farmed striped catfish Pangasianodon hypophthalmus in Vietnam. Time of immersion in 107 CFU.ml−1 had a significant effect on mortality. The immersion bacterial dose of 107 CFU/ml for 30 s resulted in a cumulative percentage mortality of 63%. Three to four days post-bacterial challenge, fish showed gross clinical signs of natural BNP and E. ictaluri was recovered and identified from these fish. Moreover, a cohabitation challenge was evaluated as an alternative challenge method, although the mortalities among the infected fish were lower at around 15%–40%. This study confirmed the horizontal transmission of E. ictaluri in striped catfish and elucidated that cohabitation challenge could be used in reproducing the disease under controlled conditions.  相似文献   

19.
The two main diseases in the pangasius catfish industry are bacillary necrosis of Pangasianodon (BNP) and motile aeromonas septicaemia (MAS), where the aetiological agents have been identified as Edwardsiella ictaluri and Aeromonas hydrophila, respectively. In this study, apparently healthy Pangasianodon hypophthalmus were exposed to E. ictaluri, A. hydrophila or both bacterial species by intraperitoneal injection or immersion. There were 20 fish per treatment group, and the bacterial isolates used for the study were recovered from natural infections of BNP or MAS in farmed Vietnamese P. hypophthalmus. The results of the experimental infections mimicked the natural disease outbreaks reported from these pathogens in P. hypophthalmus. Furthermore, it was clearly demonstrated that E. ictaluri was only recovered from the fish exposed to the bacterium and not recovered from the animals receiving A. hydrophila.  相似文献   

20.
In April 2011, there was an outbreak of an infectious disease in southern catfish, Silurus soldatovi meridionalis, (Chen) (15–20 g) in Sichuan Province, China. Two isolates, LW101 and LW102, were isolated from kidney and liver of the sick fish on brain‐heart infusion (BHI) agar and were considered to be the cause of this disease based on experimental challenges. The morphological and physiological characteristics as well as the biochemical tests of the two isolates were the same and similar to Edwardsiella ictaluri. Furthermore, the sequencing of the 16S rRNA gene and the gryB gene revealed that the isolates were highly homogeneous with E. ictaluri. On the basis of the phenotypic characteristics and phylogenetic analysis of these genes, both isolates were identified as E. ictaluri. Susceptibility of the isolates to 22 antibiotics was tested using the disc diffusion method. Both isolates showed a similar antibiotic susceptibility, which was characterized by resistance to acetylspiramycin, ampicillin, clarithromycin, penicillin, oxytetracycline, and sinomin (SMZ/TMP); the strains were susceptible to amikacin, chloramphenicol, florfenicol, roxithromycin, ciprofloxacin, norfloxacin, doxycycline, and tenemycin. To our knowledge, this is the first report of E. ictaluri infection in southern catfish.  相似文献   

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