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1.
Fang  Ling  Tan  Ge  Sin 《Journal of fish diseases》1998,21(4):273-280
A virulent strain of Aeromonas hydrophila (PPD 134/91) was obtained from the Primary Production Department, Singapore. Its major adhesin was isolated and purified by potassium thiocyanate extraction and Bio-Gel P-100 gel filtration. The ability of the protein in peak 1, termed major adhesin, to inhibit bacteria from adhering to and invading host cells was studied in vitro using epithelioma papillosum cells of carp (EPC). Results showed that a concentration of 10 μg ml–1 of this major adhesin could competitively inhibit 28% of A. hydrophila PPD 134/91 from invading EPC cells in vitro. When the concentration was increased to 40 μg ml–1, the major adhesin significantly cross-inhibited nine other virulent or weakly virulent strains of A. hydrophila. In addition, the major adhesin significantly inhibited not only another bacterial strain from the same family, Aeromonas sobria, but also strains of Vibrio spp. tested. Therefore, we suggest that the major adhesin of this virulent A. hydrophila strain has the potential to be used as a vaccine against the heterogeneous Aeromonas and Vibrio species.  相似文献   

2.
Aeromonas hydrophila is emerging as one of the major concerns in catfish aquaculture in the Southeastern United States due to recent outbreaks of motile aeromonad septicaemia (MAS) caused by virulent clonal isolates. There is no effective vaccine currently available for the prevention of MAS. In this study, two virulence‐associated proteins of A. hydrophila, aerolysin and haemolysin, were heterologously expressed in Escherichia coli cells. Recombinant aerolysin (rArl) and haemolysin (rHly) were used to immunize catfish. Both rArl‐ and rHly‐induced humoral immune response as evidenced by immunoblotting and cell agglutination; immunized fish had significantly less mortality as compared to control fish upon challenge with virulent A. hydrophila. When a mixture of rArl and rHly was used to immunize the fish, significantly higher relative per cent survival (RPS) was obtained. Sustained RPS of 71–78% were observed at 2–5 weeks post immunization. The results of this study indicated that immunization against aerolysin and haemolysin had significant impact on the establishment of pathogenesis by A. hydrophila, suggesting that these two proteins could serve as general immunogens for future development of recombinant protein vaccines.  相似文献   

3.
Low  Goh  Lim  Sin  Leung 《Journal of fish diseases》1998,21(1):55-65
Aeromonas hydrophila can enter fish cells and exist as intracellular parasites. Phase-contrast and confocal microscopy were used to examine morphological changes and various cytoskeletal components of infected fish cells. Four fish cell lines were included in this study: (1) AS, (2) BF2, (3) CHSE-214, and (4) EPC cells. Virulent but not avirulent strains of A. hydrophila PPD 134/91 invaded fish cells, causing morphological changes, and inducing microfilament (F-actin) rearrangement. Morphological changes were observed in all infected fish cell lines and could be classified into three different stages. In stage I, the cells became detached from each other and pointed ends were observed. In stage II, tubular cytoplasmic extensions formed at contact points connecting neighbouring cells. The monolayers formed a satellite-like organization and became less confluent. Finally (stage III), cells were heavily infected with bacteria, and bacteria containing vacuoles occupied most of the cells. They eventually detached and lysed. Rearrangement of F-actin was observed as local polymerization (actin clouds) in stage I and massive reorganization in stage III of infection. Actin clouds could have been induced by A. hydrophila for ‘assisted' uptake into the cells. The massive reorganization of actin in stage III may be due to products released by the bacteria and the growth of vacuoles. Pretreatment of fish cells with the microfilament inhibitors such as cytochalasins induced a similar effect. There were little if any rearrangements in intermediate and microtubule filaments during bacterial entry (stages I and II). These results suggest that A. hydrophila may bind to the surface and trigger a signal to the microfilament which then generates the force necessary for bacterial uptake.  相似文献   

4.
Aeromonas hydrophila is an opportunistic pathogen and the leading cause of fatal haemorrhagic septicaemia in fish and shellfish. Doxycycline, one of the second generation tetracyclines, has been used in fish farming to fight against infectious diseases caused by A. hydrophila due to its broad‐spectrum antimicrobial activity and lower cost. However, progressive increase in resistance of Aeromonas strains to doxycycline aroused serious concern. In this report, drug‐resistant A. hydrophilaAH10 strains were induced and selected by using a consecutive batch culture system in Mueller‐Hinton Broth (MHB) supplemented with varying concentrations of doxycycline. Five isolates (AH101‐105) were obtained from the bacterial culture induced by 25 μg/ml doxycycline for drug‐resistance analysis. Minimal inhibitory concentrations (MIC) values of all five isolates were 50 times higher than that of the parental strain AH10. All of them also displayed high‐level resistance to sulphonamides and amides. We sequenced five isolates and performed comparative genomic analysis of these draft genomes with nine A. hydrophila complete genomes from GenBank. Results showed that the pan‐genome of 14 strains contains 4,730 genes, 3,056 genes of which present in all strains. The drug‐resistance genes also showed significant difference in these genomes, which indicated dangers of indiscriminate use of antibiotics in aquaculture and the necessity of understanding the variation of antibiotic resistance of A. hydrophila. Pan‐genome analysis further revealed that no specific SNP (single nucleotide polymorphism) or InDel (insertion and deletion variation) was identified in any functional gene locus among the genomes of AH10 mutated strains, in contrast, significant CNVs (copy number variations) and SV (structure variations) for gene groups were identified in all the mutant genomes.  相似文献   

5.
This study evaluated the efficiency of differently prepared vaccines against Aeromonas hydrophila in the hybrid surubim (Pseudoplatystoma corruscans × P. reticulatum). Survival and haemato‐immunological parameters were compared between the treatments: non‐vaccinated fish (C); bacterin‐vaccinated fish (B); bacterin plus oral booster vaccinated fish (B+O); bacterin and toxoid‐vaccinated fish (B+T) and bacterin, toxoid and oral booster‐vaccinated fish (B+T+O). Fourteen‐days vaccinated fish from B+O and B+T+O were fed with an oral booster for 4 days. After 1 week, the fish were intraperitoneally challenged with 2 × 108 CFU mL?1 of A. hydrophila. Fish from the treatment B+T+O showed the lowest cumulative mortality (11.36%) 96 h after challenge, compared with other treatments (22.72–44.04%), and a relative survival of 74%. Serum immunoglobulin in B+T+O fish was higher than in other treatments. All vaccinated fish showed an increased agglutination titre when compared with non‐vaccinated fish, both before and after challenge. Fish fed with oral booster showed an increase in phagocytic percentage before and after challenge. It can be inferred that the oral booster vaccination was efficient in reducing mortality in hybrid surubim by enhancing the response against haemorrhagic septicaemia due to A. hydrophila infection.  相似文献   

6.
Two trials were conducted to determine the efficacy of fish fed live yeast Debaryomyces hansenii strain CBS 8339 on immune and antioxidant systems in leopard grouper Mycteroperca rosacea infected with Aeromonas hydrophila. Juveniles (12±0.5 g) were fed with a control diet or a D. hansenii‐supplemented diet (106 colony‐forming units per gram) for 5 weeks. The live weight of fish was registered on a weekly basis. After 4 weeks, fish from each treatment were immunocompromised with pathogenic A. hydrophila and further fed for 1 week in order to evaluate the effect on immunological and antioxidant parameters. Generally, the results showed enhanced growth performance in fish fed the diet containing yeast compared with the control. Addition of live yeast had no significant effect on the immunological parameters after 4 weeks of feeding. However, post infection with A. hydrophila fish fed the yeast‐supplemented diet resulted in a significant increase in the levels of plasmatic immunoglobulin M. Superoxide dismutase and catalase (CAT) activities were significantly higher in the yeast group. In this fish, CAT and heat shock protein 70 genes were up‐regulated before and after infection of A. hydrophila. The present study is the first one reporting that yeast (D. hansenii) can enhance immunity and resistance against A. hydrophila.  相似文献   

7.
A candidate vaccine against Aeromonas hydrophila in rainbow trout, Oncorhynchus mykiss, was developed using a bacterial lysate. To test the strength of protection, A. hydrophila challenge models were compared using injection into both the intraperitoneal (IP) cavity and the dorsal sinus (DS) with selected doses of live bacteria washed in saline or left untreated. Unlike the IP route, injection into the DS with either saline washed or unwashed cells resulted in consistent cumulative mortality and a dose response that could be used to establish a standard challenge having an LD50 of approximately 3 × 107 colony forming units per fish. Survivors of the challenge suffered significantly lower mortality upon re‐challenge than naïve fish, suggesting a high level of acquired resistance was elicited by infection. Passive immunization using serum from hyper‐immunized fish also resulted in significantly reduced mortality indicating protection can be transferred and that some portion of resistance may be antibody mediated. Vaccination of groups of rainbow trout with A. hydrophila lysate resulted in significant protection against a high challenge dose but only when injected along with Freund’s complete adjuvant. At a low challenge dose, mortality in all groups was low, but the bacterial lysate alone appeared to offer some protection.  相似文献   

8.
Aeromonas hydrophila and Gyrodactylus cichlidarum are common pathogens that induce significant economic losses in farm‐reared Nile tilapia. Nowadays, the sudden appearance of fish mortalities was exaggerated due to mixed and multiple infections. During summer 2016, mass mortality among earthen pond‐farmed Nile tilapia was reported. Clinico‐pathological, bacteriological and parasitological examinations have been demonstrated. As well, the water quality parameters were assessed. The clinical and histopathological findings of the moribund and recently dead fish were characterized by generalized septicaemic signs. The water quality parameters were significantly elevated over the permissible levels, whereas there was an elevation in nitrite (0.04 mg/L), un‐ionized ammonia (0.8 mg/L), hydrogen sulphide levels (153.1 mg/L) and organic matter content (3.79 mg/L). A. hydrophila was identified based on phenotypic characterization, API 20E features and the homology of 16S rRNA gene sequence analysis. In addition, PCR data confirmed the presence of aerolysin (aerA) and haemolysin (hly) genes in the identified A. hydrophila isolates. Gene sequencing and phylogenetic analysis based on 16S rRNA sequence confirmed that A. hydrophila H/A (accession No. MN726928) of the present study displayed 98%–99% identity with the 16S rRNA gene of A. hydrophila. Furthermore, the monogenetic trematode, G. cichlidarum was identified in the wet mounts from the skin and gills of the examined fish with a high infestation rate. In this context, it was reported that the synergistic co‐infection of A. hydrophila and G. cichlidarum with deteriorated water quality parameters could induce exaggerated fish mortalities during hot weather.  相似文献   

9.
Aeromonas hydrophila is known to be causative agent of an infection named as Bacterial haemorrhagic septicaemia or red pest in freshwater fish. The aim of this study was to develop and validate the glycoprotein‐based fish vaccine against Aeromonas hydrophila. For this aim, after identification and characterization of A. hydrophila isolates from fish farms, one A. hydrophila isolate was selected as vaccine strain. Antigenic glycoproteins of this vaccine strain were determined by Western blotting and glycan detection kit. The connection types of these glycoproteins were examined by glycoprotein differentiation kit. Two glycoproteins, molecular weights of 19 and 38 kDa, with SNA connection type were selected for use in vaccination trials. After their purification by SNA‐specific lectin and size‐exclusion chromatography, protection studies with purified proteins were performed. For challenge trials, four experimental fish groups were designated: Group I (with montanide), Group II (with montanide and ginseng), Group III [with Al(OH)3] and Group IV [with Al(OH)3 and ginseng]. The survival ratings of fish were determined, and protection was calculated as 21.56%, 29.41%, 69.83% and 78.88% in groups I, II, III and IV, respectively. In conclusion, A. hydrophila glycoproteins with Al(OH)3 and ginseng could be used as a safe and effective vaccine for fish.  相似文献   

10.
Aeromonas hydrophila and Vibrio fluvialis are the causative agents of a serious haemorrhagic septicaemia that affects a wide range of freshwater fish in China. In order to develop a bivalent anti‐A. hydrophila and anti‐V. fluvialis formalin‐killed vaccine to prevent this disease, an orthogonal array design (OAD) method was used to optimize the production conditions, using three factors, each having three levels. The effects of these factors and levels on the relative per cent survival for crucian carp were quantitatively evaluated by analysis of variance. The final optimized formulation was established. The data showed that inactivation temperature had a significant effect on the potency of vaccine, but formalin concentration did not. The bivalent vaccine could elicit a strong humoral response in crucian carp (Carassius auratus L.) against both A. hydrophila and V. fluvialis simultaneously, which peaked at 3 or 5 weeks respectively. Antibody titres remained high until week 12, the end of the experiment, after a single intraperitoneal injection. The verification experiment confirmed that an optimized preparation could provide protection for fish at least against A. hydrophila infection, and did perform better than the non‐optimized vaccine judged by the antibody levels and protection rate, suggesting that OAD is of value in the development of improved vaccine formulations.  相似文献   

11.
Egg yolk immunoglobulins (IgY) were obtained from laying hens immunized with inactivated Aeromonas hydrophila. The purified IgY was shown to inhibit the growth of A. hydrophila in vitro and the optimum concentration for inhibition of A. hydrophila‐specific IgY was 75 mg mL?1. In a subsequent challenge trial, 100 carp (200~250 g) were assigned to one of ten tanks with ten carp per tank. The fish in one tank were unchallenged whereas the remaining 90 fish were injected intraperitoneally with 100 μL of A. hydrophila at a concentration of 108 cfu mL?1. For the next 21 days, all fish were moved in their respective groups to a clean tank for 20 min day?1. The fish in four tanks (one unchallenged tank and three challenged tanks) received no treatment whereas the fish in the remaining six tanks were immersed in either 0.5 g L?1 aqueous nonspecific IgY (N = 3) or 0.5 g L?1 aqueous specific IgY (N = 3). Haemoglobin concentrations, white and red blood cell numbers as well as the mortality of specific IgY‐treated fish were significantly different from those of the control. These results suggest that passive immunization by immersion with pathogen‐specific IgY may provide a valuable treatment for A. hydrophila infection in carp.  相似文献   

12.
The specific and non‐specific immune parameters and protection of European eels (Anguilla anguilla) were evaluated after bathing eels with Aeromonas hydrophila. Two hundred eels were distributed into two equal groups and bathed with Phosphate‐buffered saline (Control group) or 1.0 × 107 cfu mL?1 A. hydrophila (Test group) for 1 h respectively. Then, eels were bled aseptically from the caudal sinus on 1, 4, 7, 14 and 28 days post treatment. The blood cells were used to evaluate the cellular immunity and the serum was used to determine the titres of specific antibody as well as the activities of superoxide dismutase (SOD) and lysozyme. Eels from both groups were challenged by intraperitoneal injection of 1.0 × 107 cfu of A. hydrophila on 28 and 42 days post bathing. The results show that eels bathed in A. hydrophila significantly (P < 0.05) enhanced the proliferation of different types of blood cells and the serum titres of anti‐A. hydrophila antibody. The Relative Percent Survival (RPS) after challenge on 28 and 42 days post bathing in Test group vs. Control group was 40% and 50% respectively. These results suggest that bathing European eels in A. hydrophila would positively affect specific as well as non‐specific immune parameters and protect against A. hydrophila infection in freshwater farming.  相似文献   

13.
Interrupting quorum sensing represents a novel anti‐infective strategy to combat bacterial pathogen, and biodegradation of quorum sensing signal AHLs has been proved to be an efficient way to control pathogenic Gram‐negative bacteria in aquaculture. In this study, the effect of Bacillus firmus sw40 as efficient AHL‐degrading strain on virulence of fish pathogen Aeromonas hydrophila and disease resistance of gibel carp Carassius auratus gibelio was investigated. The results demonstrated that in vitro the B. firmus sw40 extracellular production (ECP) was able to significantly decrease protease production, haemolytic activity and biofilm formation in A. hydrophila. Dietary administration of B. firmus sw40 (109 CFU/g) for 4 weeks significantly reduced the inflammatory cytokines TNF‐1a, TNF‐2a and IFN‐γ genes expression, antioxidant parameter MDA and GSH levels in serum and increased antioxidant enzyme SOD activity. Besides, B. firmus sw40 could significantly increase the survival of gibel carp with pathogenic A. hydrophila infection.  相似文献   

14.
This study evaluated the effects of dietary supplementation with two symbiotics in the hybrid surubim (Pseudoplatystoma corruscans × P. reticulatum) prior to and after challenge with Aeromonas hydrophila. The fish were divided into unsupplemented fish, supplemented fish with Weissella cibaria and inulin, and supplemented fish with Lactobacillus plantarum and inulin. Twenty days after being fed symbiotics, the fish were sampled for immunological, haematological, and microbiological analysis pre‐challenge. After this period, they were challenged with Aeromonas hydrophila, and after 96 h the fish were sampled for blood collection and survival. Fish fed W. cibaria and inulin from the pre‐challenge showed the highest values of lysozyme activity. Fish fed L. plantarum and inulin presented a higher number of thrombocytes and granular leukocyte PAS+ than the other fish. After challenge, fish fed both symbiotics presented an increased red blood cells number. Fish fed L. plantarum and inulin showed an increased total leucocyte count (WBC), neutrophils, and monocytes number as well as total immunoglobulin. The W. cibaria‐ and inulin‐supplemented fish showed improved haematological and immunological parameters and reduced cumulative mortality after the challenge.  相似文献   

15.
Since bacterial infection cause a significant economic loss in fish farms, it is necessary to develop rapid diagnostic tools. Interests on label‐free biosensors have been raised for the rapid detection of aquatic pathogenic bacteria but have not been extensively studied yet. Here we report a quartz crystal microbalance (QCM) immunosensor system for the rapid and simple detection of Aeromonas hydrophila, a pathogen for fish and human, in comparison with a conventional indirect ELISA method. In QCM immunosensor system, an antibody against A. hydrophila was covalently cross‐linked to the gold surface of sensor chip and bacterial attachment was monitored as real‐time frequency shifts within 5 min. The frequency shifts were very positively related to the amounts of bacterial cells between 6.25 and 100 μg corresponding to 6 × 106 to 108 CFU with a high specificity. The QCM immunosensor was also able to detect bacterial cells in fish tissue extract in a dose‐dependent manner. Indirect ELISA also showed the dose‐dependent reaction and the amplified signal may allow a lower detection limit. However, QCM immunosensor system showed a more linear and reliable standard curve with R2 value of almost 1 (0.9999). Moreover, detection of the bacteria was much quicker and simpler.  相似文献   

16.
This study sought to isolate and characterize lactic acid bacteria (LAB) from stomach of adult snakehead fish, Channa striatus, to be used as probiotics for freshwater fish. A total of 13 strains were isolated from the stomach of 10 fish, and 4 of these belonged to LAB. Strain LAB‐3 showing highest in vitro growth inhibition of Aeromonas hydrophila in a disk diffusion test was identified as Lactobacillus fermentum by conventional and molecular techniques and evaluated in vitro through various tests. The bacterium could grow at pH 3–8; but the optimum growth was observed at pH 6. Moreover, LAB‐3 grew at 0.15 and 0.3% bile salt concentrations, from 15 to 45 C, and at 4% NaCl. L. fermentum showed in vitro inhibitory activity against three fish pathogens, A. hydrophila, Pseudomonas aeruginosa, and Shewanella putrefaciens, tested by disk diffusion and well diffusion methods. Antibiotic sensitivity tests indicated that L. fermentum was resistant to streptomycin, gentamycin, and kanamycin, intermediate to tetracycline, but sensitive to chloramphenicol, amoxicillin, and ampicillin. Challenge test by using A. hydrophila showed that survival of snakehead was significantly (P < 0.05) improved when 2 × 106 LAB‐3/g was supplemented to the diet. Therefore, this study suggests that L. fermentum might be a promising probiotic in snakehead aquaculture .  相似文献   

17.
An 84‐day feeding trial was carried out to evaluate the effects of aqueous Psidium guajava leaf extract (PGE) on growth, intestinal morphology, physiology, immune response and susceptibility of Oreochromis niloticus to Aeromonas hydrophila. Diets containing 0% (P0), 0.25% (P1), 0.50% (P2), 0.75% (P3) and 1.00% (P4) PGE were fed to triplicate groups of fish (mean weight; 1.32 ± 0.04 g) for 84 days. After the 84‐day feeding trial, test fish were injected with pathogenic A. hydrophila and then fed for 14 days. More feed were consumed in groups of fish fed PGE‐treated diets and resulted in significantly higher weight gain and feed intake. Incidentally, there was an increase in the calculated area of absorption of fish fed PGE diets, as accounted for by marginally higher villi length and width. Antioxidant and immune response were improved with PGE inclusion in diets as total protein, superoxide dismutase, glutathione peroxidase and glutathione S‐transferase significantly increased (p < 0.05) in fish fed PGE diets. Results of the challenge test with A. hydrophila revealed that the highest mortality (100%) was recorded in P0. This study revealed that inclusion of P. guajava extract in the diet of O. niloticus improved growth, nutrient utilization, immune system and survival of O. niloticus fingerlings.  相似文献   

18.
The occurrence of pathogenic bacteria, Aeromonas hydrophila, in farm‐raised fish requires urgent attention. Continuous and indiscriminate use of antibiotics as growth promoters and disease control agents in aquaculture have been discouraged because of the risk of development of antibiotic‐resistant bacterial strains. There is steady interest in the use of botanicals, such as clove, Eugenia caryophyllata, buds extract (ECBE), as alternatives. Hence, the present study evaluated the effect of dietary ECBE supplementation on the growth performance, physiological, antioxidant, and immunity biomarkers of African catfish, Clarias gariepinus. Fish (11.7 ± 0.5 g) were fed diets containing 0.0 (control), 5.0, 10.0, or 15.0 g ECBE/kg diet up to apparent satiation twice daily for 12 weeks. After the feeding trial, fish from each treatment were challenged with A. hydrophila infection by intraperitoneal injection and kept under observation for 14 days to record any abnormal clinical signs and daily mortality. The results demonstrated that fish performance and feed intake were significantly enhanced with increasing ECBE levels, and its optimum level is 15 g/kg diet. Further, the dietary ECBE increased significantly the intestinal villi length/width and absorption area in a dose‐dependent manner. There are significant progressive increases in the values of red blood cells, hemoglobin, hematocrit, white blood cells, platelets, lymphocytes, and heterocytes, while monocytes, eosinophil, and basophils decreased significantly due to dietary ECBE in a dose‐dependent manner. Highest glucose, cholesterol, total protein, globulin, and albumin‐globulin ratios, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), urea, and creatinine values were found in fish fed 15 g ECBE/kg diets, while lowest values were recorded in fish fed the control diet. Despite the high AST and ALT values, no visible lesions or damage were observed in the liver cells of fish fed ECBE‐enriched diets. In addition, the inclusion of ECBE in fish diets enhanced the antioxidant and immunity capacity. Fish mortality after the bacterial challenge was higher in fish fed the control diet (82.3%) than those fed ECBE‐enriched diets. The lowest fish mortality was observed in fish fed the 15 ECBE/kg diet (4.7%) [Correction added on 16 November 2018: this section has been revised for clarity.].  相似文献   

19.
The outer membrane protein of Aeromonas hydrophila is a potential candidate for vaccine development. In this study, after cloning and expression of ompTS, 270 common carp, weighing 44 ± 5.7 g divided into five groups, were injected intraperitoneally twice with 3‐week intervals. Groups included the following: PBS, PBS plus Freund's adjuvant, recombinant protein, recombinant protein plus Freund's adjuvant and 20 fish as negative control. Two weeks after the second injection, 30 fish of each group were challenged with a dose of 2 × LD50 of Aeromonas hydrophila and RPS was measured. The antibody level was measured using ELISA test. The protection of recombinant protein in the immunized fish with and without adjuvant, respectively, was about 82.61% and 78.26% (the protection of recombinant protein electroeluted from an SDS–PAGE with and without adjuvant, respectively, was about 78.62% and 69.57%). The average of antibody level in recombinant protein with and without adjuvant was significantly higher than the PBS group (p < .05). The ability of recombinant ompTS to increase the antibody level and to protect the fish from challenge by A. hydrophila demonstrated that recombinant ompTS protein injection can be used to immunize common carp against A. hydrophila infection.  相似文献   

20.
Under experimental challenges, the gastrointestinal (GI) tract of fish has been proposed as an infectious route of several pathogenic bacteria. Is this also the case for diseased fishponds? A field research was conducted to verify this hypothesis. A crucian carp (Carassius carassius) reared fishpond with motile Aeromonas septicaemia outbreak was sampled in this study. A total of 62 strains of Aeromonas hydrophila were isolated and identified. The clonal relationship among these strains was determined by sequencing the gyrB gene, ERIC‐PCR, RAPD‐PCR, and the presence of seven virulence genes. Strains with identical genotypes were further confirmed as the same clone by multilocus sequence typing analysis. Experimental infection assays were also conducted in zebrafish (Danio rerio). The results show that the same clone strains identical to those in the blood of diseased fish existed in the intestinal digesta of diseased and uninfected fish. Regardless of their origins, all these strains were highly pathogenic to zebrafish. The result indicates that pathogenic strains of A. hydrophila had existed in the GI tract of fish before the infection occurred. This increases our knowledge on infectious route of A. hydrophila in crucian carp.  相似文献   

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