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1.
Abstract

β-hydroxy-b-methylbutyrate (HMB), a leucine catabolite, has been shown to cause increased disease resistance and growth in animal production. A vaccine produced from formalin killed bacteria and concentrated extracellular products of the ARS-98-60 Streptococcus iniae isolate has been used for the prevention of streptococcal disease in Nile tilapia, Oreochromis niloticus. In the present study, the effects of feeding HMB were determined in tilapia vaccinated by intraperitoneal (IP) injection of the S. iniaevaccine or unvaccinated (controls). Nile tilapia were fed diets containing either 0, 12.5, 25, or 50 mg HMB/kg diet for 14 days. The mean daily growth rate and feed efficiency showed no significant (P> 0.05) differences between the treatment groups. Dietary HMB supplementation did not enhance antibody production in unvacci-nated Nile tilapia following challenge. Dietary HMB supplementation did not enhance the survival of vaccinated Nile tilapia following challenge injection with 1 X108 CFU of S. iniae.  相似文献   

2.
This study was conducted to characterize the causative agent of streptococcosis in tilapia (Oreochromis niloticus) and control of Streptococcus infection by means of garlic (Allium sativum) supplementation. The morphological, biochemical and polymerase chain reaction amplification confirmed 11 isolates belong to Streptococcus iniae from the infected fish eyes and tissue samples. Random screening of 12 well‐known medicinal plant parts against S. iniae revealed the garlic extract as the most effective herbal recovery against Streptococcus infection. In vivo challenge test with dietary supplementation of garlic powder significantly improved survival rates of fish against S. iniae infections, and modulate the microbial community and cytokine gene expression profiling in the intestine of the experimental tilapia. Among the two garlic supplemented treatments, 1.0 g garlic supplemented diet significantly increased (p < 0.05) the survival rates of tilapia and the gut bacterial operational transitional units abundance for Proteobacteria and Tenericutes, the phyla associated with healthy intestinal flora. The bacterial diversity index also found high with garlic supplemented diets. Significant upregulations of IL‐10 and IL‐17F gene expression in the intestinal tissue were observed with 1.0 g garlic supplemented diet where IL‐8 and IL‐1β expression levels were relatively static. The dietary supplementation of garlic, therefore, could be effective in the prevention of S. iniae infection in fish.  相似文献   

3.
Vaccination strategies have traditionally been used as preventative or prophylactic measures against disease (prophylactic immunization) in uninfected fish. Alternatively, therapeutic or remedial measures, such as antibiotic administration, are commonly employed to treat disease in infected fish. Vaccination as a therapeutic measure (therapeutic immunization), however, has not been adequately explored in sub‐clinically infected fish. Therapeutic and prophylactic immunization with three Streptococcus iniae vaccines, formalin‐killed whole S. iniae cells (FKC vaccine), concentrated S. iniae extracellular products (greater than 2 kDa) (ECP vaccine) and a combination of killed cells and extracellular products (FKC+ECP vaccine), were tested in hybrid striped bass, Morone chrysops×Morone saxatilis, previously naturally infected with S. iniae. Fish (mean weight 10.0 g) were injected intraperitoneally (IP) or intramuscularly (IM) with one of each of the vaccines, tryptic soy broth (TSB‐control) or non‐injected (non‐injected control) to evaluate therapeutic effects (Trial 1). Survivors of the natural infection and ECP and FKC+ECP vaccine immunization and another lot of non‐injected control fish were immersion challenged with 1.47 × 106 CFU of S. iniae mL?1 at 44 days post‐immunization to evaluate vaccine efficacy (Trial 2). Hybrid striped bass (1.0 g) were also IM injected with S. iniae ECP vaccine at an aquaculture facility and immersion challenged with 1.47 × 106 CFU of S. iniae mL?1 12 weeks post‐immunization (Trial 3). The ECP and FKC+ECP vaccines, regardless of injection route, significantly (P<0.001) increased survival in asymptomatic, sub‐clinically infected fish thereby providing therapeutic merit. Hybrid bass immunized IP or IM had mean per cent survival values ranging from 78 to 96 at 44 days post‐immunization (Trial 1) and 69–97 post challenge (Trial 2). Survival of fish injected with TSB or immunized with FKC vaccine was significantly lowered and ranged from 12 to 13 by IP injection and 40 to 50 by IM injection and thus, the FKC vaccine had no therapeutic effect. The survival of hybrid striped bass IM immunized with S. iniae ECP vaccine in field Trial 3 was 91 and the RPS was 83. These results demonstrate that therapeutic immunization using S. iniae ECP and FKC+ECP vaccines can control a natural S. iniae infection. Furthermore, S. iniae ECP or FKC+ECP vaccines can also be used prophylacticly to protect hybrid striped bass against subsequent pathogen challenge.  相似文献   

4.
This study determined the growth performance and acquired resistance of Nile tilapia, Oreochromis niloticus (L.) that survived Streptococcus iniae infection. Tilapia were challenged with three doses of S. iniae (8.8 × 103, 8.8 × 104 and 8.8 × 105 CFU fish?1 for low, medium and high challenges respectively). Groups of non‐injected and tryptic soy broth‐injected fish were maintained as controls. Significantly (P<0.05) higher mortality (45.0%) occurred in the high challenge treatment than in the low challenge treatment group (29.6%). The medium challenge group had mortality (36.3%) that did not differ significantly from the high or low treatment. Few fish died in the non‐injected and broth‐injected treatments (3.4% and 0.8% respectively). The tilapia that survived S. iniae infection used to assess growth performance were selected from survivors without gross clinical signs of disease. These fish were randomly stocked at a rate of 30 fish into each 57 L aquarium in triplicate and fed to apparent satiation for 8 weeks. No significant differences were detected in weight gain, feed intake, feed efficiency ratio or survival between S. iniae‐survived tilapia and the control treatments following the 8‐week growth performance trial. Following the 8‐week feeding study, tilapia were challenged with 1 × 106 CFU fish?1 of S. iniae to assess acquired immunity. Mean cumulative mortality was significantly higher (P<0.05) in the control treatments (41.7% for the non‐injected and 43.3% for the broth‐injected fish) than in the low, medium and high challenge treatments (7.4%, 3.3% and 8.3% respectively). Serum protein was significantly (P<0.05) elevated in the S. iniae‐survived tilapia that were subsequently challenged when compared with controls challenged for the first time. Agglutinating antibody titre was significantly higher in the fish in the medium and high challenge treatments, compared with the control fish challenged for the first time. The results suggest tilapia that survive S. iniae challenge without showing overt disease signs performed as well as non‐infected tilapia. Further, the S. iniae‐survived tilapia challenged following the 8‐week growth performance trial gained acquired resistance to homologous S. iniae challenge.  相似文献   

5.
Streptococcus spp. are major pathogenic bacteria associated with massive mortality in tilapia. This study investigated the phenotypic and genotypic characterization of Streptococcus agalactiae (GBS) and Streptococcus iniae (S. iniae) isolated from tilapia in river-based floating cage and earthen pond farms in northern Thailand. Isolates were identified by biochemical and molecular analyses. Capsular typing, enterobacterial repetitive intergenic consensus polymerase chain reaction and multilocus sequence typing were performed to investigate the genetic relatedness. Six and one isolates were confirmed as GBS and S. iniae, respectively. All Streptococcus spp. isolates were obtained from 4 river-based cage farms (4/33), while samples collected from earthen pond farms (N = 28) were negative for streptococcosis. All GBS with serotype Ⅲ and sequence type (ST) 283 was observed. The β-haemolytic GBS isolates were resistant to five antimicrobials, while the S. iniae was susceptible to all antimicrobials. This study indicates both GBS and S. iniae are the major bacterial pathogens responsible for streptococcosis infection in farmed tilapia of northern Thailand with GBS as dominant species. This survey highlights that the river-based cage farms seriously impact on the healthy development of the tilapia industry.  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.
Streptococcosis causes economic losses due to mass mortality at all culturing stages in Nile tilapia, Oreochromis niloticus, and red tilapia, Oreochromis sp., farming throughout Thailand. Diseased tilapia collected from outbreak areas during 2003–2012 were examined using histopathological, biochemical, and molecular tools. Infected fish showed clinical signs of septicemia, and bacteria were found in visceral organs. All gram‐positive cocci isolates were negative to catalase and oxidase, and exhibited β‐hemolysis; however, they possessed various biochemical profiles. PCR amplification of the 16S rRNA gene was used for 165 samples, and resulted in identification of 143 (86.67%) with Streptococcus agalactiae and 14 (8.48%) with Streptococcus iniae, and 8 (4.85%) with mixed infection. High similarity (≥98%) of 16S rRNA gene sequences to the reference strain S. agalactiae (accession no. EF092913) and S. iniae ATCC29178 type strain was observed in the typing of S. agalactiae and S. iniae from Thai farmed tilapia. This investigation documented that at least two species of streptococcal bacteria, S. agalactiae and S. iniae, were involved in tilapia streptococcal infection in Thailand. The molecular recognition of the etiologic agents showed that S. agalactiae was the dominant species that cause disease in all culture areas, whereas S. iniae were discovered only in cases from the northeastern and central regions.  相似文献   

8.
Streptococcus agalactiae is an important pathogen in fish, causing great losses of intensive tilapia farming. To develop a potential live attenuated vaccine, a re‐attenuated S. agalactiae (named TFJ‐ery) was developed from a natural low‐virulence S. agalactiae strain TFJ0901 through selection of resistance to erythromycin. The biological characteristics, virulence, stability and the immunization protective efficacy to tilapia of TFJ‐ery were determined. The results indicated that TFJ‐ery grew at a slower rate than TFJ0901. The capsule thickness of TFJ‐ery was significantly less (p < 0.05) than TFJ0901. When Nile tilapia were intraperitoneally (IP) injected with TFJ‐ery, the mortality of fish was decreased than that injected with TFJ0901. The RPS of fish immunized with TFJ‐ery at a dose of 5.0 × 107 CFU was 95.00%, 93.02% and 100.00% at 4, 8 and 16 weeks post‐vaccination, respectively. ELISA results showed that the vaccinated fish produced significantly higher (p < 0.05) antibody titres compared to those of control at 2 or 4 weeks post‐vaccination. Taken together, our results suggest that erythromycin could be used to attenuate S. agalactiae, and TFJ‐ery is a potent attenuated vaccine candidate to protect tilapia against S. agalactiae infections.  相似文献   

9.
Francisella noatunensis subsp. orientalis is a causative agent of systemic granulomatous disease in tilapia. The present study was designed to understand the genetic and phenotypic diversities among Taiwanese Fno isolates obtained from tilapia (n = 17) and green Texas cichlid (Herichthys cyanoguttatus) (n = 1). The enzymatic profiles of the isolates were studied using the API ZYM system. Phylogenetic tree analysis of the 16S rRNA and housekeeping gene and pulsed‐field gel electrophoresis (PFGE) were carried out to determine the genotypic characters of all isolates. The phylogenetic tree showed similarity of 99%–100% nucleotide sequences of 16S rRNA and housekeeping genes compared to the Fno references genes from GenBank database. Comparatively, the results revealed an identical profile of enzymatic and PFGE pattern which was distincted from that of F. philomiragia. To understand the pathogenicity, the isolates were intraperitoneal injected to tilapia the gross lesions were observed concomitant with natural outbreak. Median lethal dose upon Nile tilapia and red tilapia were 9.06 × 103 CFU/fish and 2.08 × 102 CFU/fish, respectively. Thus, our data provide understanding the epidemiology of Taiwanese Fno isolates, and help in development of future control and prevention.  相似文献   

10.
Columnaris disease can be problematic in tilapia (Oreochromis spp.) production. An understanding of the pathogenesis and virulence of Flavobacterium columnare is needed to develop prevention strategies. The objective of this study was to determine the virulence of genetically defined isolates of F. columnare in sex‐reversed hybrid tilapia, Oreochromis niloticus (L.) × O. aureus (Steindachner). A series of immersion challenge trials were performed using isolates of the five established genomovars of F. columnare: I, II, II‐B, III and I/II. The mean per cent mortality of fish challenged with genomovar I, II and III isolates ranged from 0 to 100, 3.3–78 and 3.3–75%, respectively. The mean per cent mortality of fish challenged with genomovar II‐B ranged from 35 to 96.7%, and the only genomovar I/II isolate tested caused no mortality. Contrary to previous work in other fish species, there did not appear to be an association between F. columnare genomovar and virulence in tilapia. The challenge model used resulted in acute mortality. An alternative challenge model was tested by cohabitating healthy fish with dead fish infected with F. columnare. This method resulted in rapid appearance of clinical signs and mortality, suggesting the potential for F. columnare to increase in virulence upon growth on/in a fish host.  相似文献   

11.
Streptococcus iniae is one of the most serious aquatic pathogens, causing significant economic losses in marine and freshwater species, including Asian seabass (Lates calcarifer). Controlling this gram‐positive bacterial pathogen has been an issue in aquaculture systems, due to the combined effects of aquaculture intensification and climatic impacts. To date, there have not been any genetic parameter estimates for S. iniae resistance in Asian seabass. The main aim of this study was to examine genetic variation in S. iniae resistance and its genetic correlations with growth and cannibalism in Asian seabass families produced from a breeding programme for high growth in 2016 and 2017. The study included a total of 5,835 individual fish that were offspring of 41 sires and 60 dams (31 half‐sib and 34 full‐sib families). The experimental fish were challenged by intraperitoneal injection with a volume containing 105 CFU (colony‐forming unit)/fish. Resistance to S. iniae was measured as survival rate at 6 hr, 3, 5, 7, 10 and 15 days post‐challenge test. There were significant variations in S. iniae resistance among families at different observation periods (ranging from 24.4% to 80%). Restricted maximum‐likelihood method and mixed model analysis were applied to estimate heritability for S. iniae resistance. The heritability for S. iniae resistance ranged from 7% to 18% across different statistical models used. The common full‐sib effects accounted for 0.1%–2% of the total variation in resistance to S. iniae. Genetic correlations of the S. iniae resistance at 6 hr and 3 days with later post‐challenge test periods were low to moderate. However, these estimates for S. iniae resistance between successive measurement times (5, 7, 10 and 15 days) were high and close to 1. The genetic correlations of resistance with body weights at 180, 270 and 360 days post‐hatch were not significant as well with cannibalism. It is concluded that there is substantial additive genetic variation in resistance to S. iniae, suggesting there is potential for genetic improvement of Asian seabass for resistance to S. iniae through selective breeding.  相似文献   

12.
Streptococcosis cause severe losses for global tilapia farming, especially in developing countries. The aim of this study was to identify and characterize streptococci recovered from Nile tilapia farmed in the Philippines. Moribund and apparently healthy fish were sampled from grow-out cages, ponds and hatcheries. Clinical signs observed included exophthalmia, eye opacity, ascites, lethargy, erratic swimming and haemorrhages. Results showed that both Streptococcus iniae and Streptococcus agalactiae were associated with disease in these sites. Consistent with global reports, including those from South-East Asia, S. agalactiae was more widespread than S. iniae. Molecular serotyping of the S. agalactiae isolates identified the serotype Ia and serotype Ib. Histopathological findings were meningitis, meningoencephalitis and septicaemia. Identical virulence profiles were found for all strains of S. iniae, while S. agalactiae strains were separated into virulence profile I and profile II. All strains were susceptible to the tested antibiotics and resistant to oxolinic acid. Only S. agalactiae serotype Ib showed resistance to sulphamethoxazole–trimethoprim. This is the first study from the Philippines to characterize the streptococci involved in disease outbreaks in tilapia aquaculture. Outputs from this study will promote the development of efficacious disease control strategies in tilapia farming for the Philippines and South-East Asia.  相似文献   

13.
Streptococcus iniae is an important bacterial pathogen of fish, causing up to 50% mortality in stocks, which has recently been associated with human infections. To determine whether S. iniae isolates from humans and fish are similar, the present authors examined the biochemical profiles and genetic relatedness of these isolates by random amplified polymorphic DNA (RAPD) analysis and repetitive primer polymerase chain reaction(REP PCR). The biochemical profiles differentiated between the human and fish isolates of S. iniae using pyrrolidonyl arylamidase, arginine dehydrogenase, ribose, β-glucoronidase and glycogen as markers. These biochemical results suggest that the fish and human S. iniae isolates are genetically different. However, RAPD and REP PCR do not have the discriminatory power to differentiate between these streptococcus isolates using five different RAPD primers and BoxA primer.  相似文献   

14.
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15.
Commercially available yeast and yeast subcomponents consisting mainly of β-glucan or oligosaccharide feed additives were added to diets of juvenile (12–18g) Nile tilapia (Oreochromis niloticus) at rates recommended by suppliers. Three experiments were conducted following a basic protocol with varied rates of supplementation, duration of feeding, and stocking densities. Experimental diets were fed twice daily to apparent satiation for a period of two or four weeks, at the end of which feed consumption and weight gain were measured. Following the experimental feeding period, serum components, including protein and immunoglobulin concentrations, as well as lysozyme and complement activities, were measured. A disease challenge was conducted with pathogenic isolates of Streptococcus iniae or Edwardsiella tarda. Weight gains were not significantly different in fish fed the supplemented diets when compared to the control diet. There were significant differences in fed intake within individual experiments; however, this effect was not consistent in all three experiments. Overall feed efficiency was not significantly affected by diet. There were no differences in serum components of fish sampled at two or four weeks. Fish fed the experimental diets did not have lower mortality or morbidity after disease challenge compared to fish fed the control diets. Specific antibody against S. iniae or E. tarda measured by ELISA did not reveal differences in the fish surviving the challenge. We conclude that the incorporation of these commercial yeast component products into the diet of juvenile Nile tilapia at these rates and for these feeding periods had no effect on growth, serum components, antibody responses, or survival following S. iniae or E. tarda infection.  相似文献   

16.
This study was conducted to evaluate the effect of dietary levels of distiller’s dried grains with solubles (DDGS) on growth, body composition, hematology, and resistance of Nile tilapia, Oreochromis niloticus, to Streptococcus iniae challenge. Five isocaloric diets containing DDGS at levels of 0, 10, 20, and 40%, and 40% DDGS + lysine (Diets 1–5) as partial replacements of a combination of soybean meal (SBM) and corn meal (CM) on an equal protein basis were fed to juvenile Nile tilapia (9.41 ± 0.14 g) for 10 wk. Fish fed Diet 4 had the lowest weight gain (WG), feed efficiency ratio, protein efficiency ratio (PER), and whole‐body protein. Supplementation of lysine to the 40% DDGS diet (Diet 5) improved WG and PER. Hematological and immunological parameters were not affected by dietary treatment. There were no significant differences among the average number of days to first mortality after S. iniae challenge and cumulative mortality 14 d postchallenge among fish in various treatments. DDGS can be incorporated in tilapia diet at a level of 20% as a substitute for a combination of SBM and CM without affecting their growth performance, body composition, hematological parameters, immune response, and resistance to S. iniae infection.  相似文献   

17.
The aim of this study is the development and evaluation of a rapid and accurate quantitative PCR (qPCR)‐based protocol for detection of zoonotic pathogen Streptococcus iniae in bacterial cultures and tissues of diseased fish. For this purpose, the lactate permease‐encoding (lldY) gene was selected as a target for the design of S. iniae‐specific primers based on comparative genomic analysis using 45 sequences retrieved from NCBI genome database. Specificity and applicability of these primers were tested using 115 bacterial strains and fish tissues infected with S. iniae. Sensitivity, reproducibility and efficiency of qPCR assay were also determined. The developed qPCR assay showed 100% specificity with pure bacterial cultures or DNA extracted from S. iniae or tissues of fish infected with the bacterium. The method has high sensitivity with a detection limit of 1.12 × 101 amplicon copies per assay (equivalent to 2 × 10–9 ng/µl) using bacterial DNA and of 1.44 × 101 gene copies in tissues of fish infected with S. iniae. In conclusion, this qPCR protocol provides an accurate and sensitive alternative for the identification of S. iniae and its detection on fish tissues that can be implemented as a routine tool in microbiological laboratories.  相似文献   

18.
In this study, four essential oils—cinnamon oil, leech lime oil, lemongrass oil, and turmeric oil—were examined for their antimicrobial activities against Streptococcus iniae, a bacterium that is pathogenic in fish, in which it causes streptococcosis. Cinnamon oil was the most potent antimicrobial agent among these oils, with a minimal inhibitory concentration (MIC) of 40 μg/ml. By using gas chromatography–mass spectrometry (GC–MS), it was found that the major components of cinnamon oil were cinnamaldehyde (90.24), limonene (2.42%), cinnamyl acetate (2.03%), linalool (1.16%), and α-terpineol (0.87%). Of these compounds, only cinnamaldehyde exhibited antimicrobial activity against S. iniae, with an MIC of 20 μg/ml. In an in vivo trial, no mortality was apparent in fish fed on fish diets supplemented with 0.4% (w/w) of cinnamon oil and with 0.1% (w/w) of oxytetracycline 5 days prior to infection with S. iniae. These results indicate that cinnamon oil had a protective effect on experimental S. iniae infection in tilapia, and thus has the potential to replace the antibiotics used to control this disease.  相似文献   

19.
Two experiments were conducted to examine the effect of commercially available beta‐glucan (Macrogard) and nucleotide (Aquagen) on the resistance to Streptococcus iniae infections in vaccinated or nonvaccinated juvenile red‐tail black sharks (Epalzeorhynchos bicolor, RTB) (1.4 ± 0.4 g weight total (WT), 5.6 ± 0.5 cm total length (TL)). The immunostimulants were added to a control diet formulated without any yeast source following the recommended doses of 1 g/kg feed for the beta‐glucan and 2 g/kg feed for the nucleotide. Beginning 4 d after introduction into tanks, fish were fed the experimental diets for 24 d, at 3% body weight per day, divided into two feedings. At the end of this period, fish were challenged by an intracoelomic injection of S. iniae. In the first experiment, both vaccinated and nonvaccinated fish were fed one of the two immunostimulants. In the second experiment, only vaccinated fish were fed the immunostimulants. Fish were vaccinated a week after being introduced into the system and challenged by intracoelomic injection with 1.5 × 105 S. iniae colony‐forming units /fish after three additional weeks; mortality was recorded for 2 wk after the bacterial challenge. In the first experiment, the mortality of both vaccinated and nonvaccinated fish fed beta‐glucan (23 ± 7% and 82 ± 1%, respectively) or nucleotide (28 ± 6% and 86 ± 5%, respectively) was significantly lower than the mortality of the control groups (35 ± 4% and 93 ± 5%, respectively), but there was no significant difference in mortality between fish fed beta‐glucan or nucleotide. In the second experiment, the mortality of vaccinated fish fed beta‐glucan (25 ± 7%) or nucleotide (43 ± 9%) was significantly lower than that of vaccinated fish fed the control diet (69 ± 7%). In both experiments, there was no significant difference in growth rate among fish fed immunostimulants or the control diet. The results of this investigation demonstrated the efficacy of beta‐glucans and nucleotides in increasing resistance to S. iniae in RTB sharks.  相似文献   

20.
Streptococcus iniae has emerged as an important fish pathogen over the past few decades causing high losses in aquaculture farms all over the world. At least 27 species of fish have been documented to be infected by S. iniae, including cultured and wild populations. In August and October 2013, a serious infectious disease characterized by body ulcer, internal organs haemorrhages and nodules showing on epicardium occurred on the Acipenser baerii farms in Ya'an country, China. Histological examination revealed a multisystemic, necrotising inflammatory response that was particularly marked in liver, kidney, heart and brain. Mass mortality (>40%) was observed in infected fish and two Gram‐positive cocci (Ab130920 and Ab131025) were obtained from kidneys and livers of diseased fish. Experimental infections with these two isolates resulted in marked symptoms in the sturgeons similar to those observed in natural outbreaks, and the LD50 values of the two isolates were 5.1 × 105 and 6.4 × 105 cfu per fish respectively. The two microorganisms were identified as S. iniae through physiological and biochemical tests, 16S rRNA and lctO gene sequence analysis. Both two isolates showed a similar antibiotic susceptibility, which were sensitive to ampicillin, amoxicillin, cefazolin, amikacin, deoxycycline, florfenicol, azithromycin, ciprofloxacin, vancomycin and resistant to streptomycin, gentamicin, kanamycin, norfloxacin and sinomin (SMZ/TMP). Multiplex PCR assay for virulence genes showed both isolates possessed six main virulence genes: simA, scpI, pdi, pgm, cpsD and sagA genes. These results indicated that S. iniae could act as a pathogen of farmed A. baerii. This is the first report of S. iniae infection associated with mass mortality in A. baerii.  相似文献   

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