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1.
CD3 is an important membrane molecule of mature T cells. TCR‐CD3 complex plays important roles in the activation and signal transduction of T cells. In this study, the CD3ε (OnCD3ε) gene was cloned from Nile tilapia (Oreochromis niloticus), and its tissue distribution was detected by qPCR. The expression changes in CD3ε were analysed after three challenges (S. agalactiae, A. hydrophila and poly (I:C)) in vivo and in vitro. The open reading frame (ORF) of OnCD3ε contains 531 bp, encoding 176 amino acids, which found that OnCD3ε consists of conserved amino acid residues and motifs (cysteine residues, CXXC motif, immunoreceptor tyrosine‐based activation motifs and PxPDY). In addition, tissue distribution displayed that OnCD3ε has the highest expression in thymus and significant expression level in mucosal immune‐related tissues (intestine and gills). In vivo, all three challenges could significantly up‐regulate the expression of CD3ε in the head kidney and spleen. For further in vitro assays, after poly (I:C) stimulation, OnCD3ε appeared significant up‐regulation at 3 hr post stimulation, and two pathogenic bacteria also induce significant up‐regulation of OnCD3ε in spleen leucocytes (12 hr). These results suggested that OnCD3ε was likely to get involved in host immune response against pathogenic challenges.  相似文献   

2.
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3.
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   

4.
Streptococcus agalactiae has become one of the most important emerging pathogens in the aquaculture industry and has resulted in large economic losses for tilapia farms in China. In this study, three pairs of specific primers were designed and tested for their specificities and sensitivities in quantitative real‐time polymerase chain reactions (qPCRs) after optimization of the annealing temperature. The primer pair IGS‐s/IGS‐a, which targets the 16S‐23S rRNA intergenic spacer region, was finally chosen, having a detection limit of 8.6 copies of S. agalactiae DNA in a 20 μL reaction mixture. Bacterial tissue tropism was demonstrated by qPCR in Oreochromis niloticus 5 days post‐injection with a virulent S. agalactiae strain. Bacterial loads were detected at the highest level in brain, followed by moderately high levels in kidney, heart, spleen, intestines, and eye. Significantly lower bacterial loads were observed in muscle, gill and liver. In addition, significantly lower bacterial loads were observed in the brain of convalescent O. niloticus 14 days post‐injection with several different S. agalactiae strains. The qPCR for the detection of S. agalactiae developed in this study provides a quantitative tool for investigating bacterial tissue tropism in infected fish, as well as for monitoring bacterial colonization in convalescent fish.  相似文献   

5.
Streptococcus agalactiae (Group B Streptococcus, GBS) is associated with diverse diseases in aquatic animals. The capsule polysaccharide (CPS) encoded by the cps gene cluster is the major virulence factor of S. agalactiae; however, limited information is available regarding the pathogenic role of the CPS of serotype Ia piscine GBS strains in fish. Here, a non‐encapsulated mutant (Δcps) was constructed by insertional mutagenesis of the cps gene cluster. Mutant pathogenicity was evaluated in vitro based on the killing of whole blood from tilapia, in vivo infections, measuring mutant survival in tilapia spleen tissues and pathological analysis. Compared to wild‐type (WT) GBS strain, the Δcps mutant had lower resistance to fresh tilapia whole blood in vitro (p < 0.01), and more easily cleared in tilapia spleen tissue, and was highly attenuated in tilapia and zebrafish. Additionally, compared to the Δcps mutant, numerous GBS strains and severe tissue necrosis were observed in the tilapia spleen tissue infected with WT strains. These results indicated that the CPS is essential for GBS pathogenicity and may serve as a target for attenuation in vaccine development. Gaining a better understanding of the role, the GBS pathogenicity in fish will provide insight into related pathogenesis and host–pathogen interactions.  相似文献   

6.
This study was conducted to determine the systemic, mucosal immunity and protective capacity of the feed‐based adjuvant vaccine (FAV) of Streptococcus agalactiae following oral vaccination against streptococcosis in tilapias. Two hundred and sixteen red tilapia fish were divided into three major groups. Each major group consisted eight tilapia kept in nine 2000 L glass aquaria. At day 0, all fish from the FAV group were fed with feed that had been incorporated with an adjuvant, while fish in the feed‐based vaccine (FNV) group were fed with vaccine incorporated into the pellet without adjuvant. Fish in the control‐unvaccinated group, FC, were fed with normal commercial pellet. Booster dose was performed on day 14 post immunization. Fish from each group were sacrificed on a weekly basis for the entire 7 weeks. Serum, body mucus and gut lavage fluid were evaluated for antibody responses by indirect ELISA, while histological examination was carried out on the gut following intraperitoneal challenge. The FAV group had a significantly higher protection (P < 0.05) following challenge with 3.4 × 109 CFU mL?1 of live S. agalactiae than FNV group. This level of protection may be due to high antibody responses, increase in size of gut‐associated lymphoid tissue and high number of lymphocytes in the FAV group.  相似文献   

7.
Streptococcus agalactiae infections in fish are predominantly caused by beta‐haemolytic strains of clonal complex (CC) 7, notably its namesake sequence type (ST) 7, or by non‐haemolytic strains of CC552, including the globally distributed ST260. In contrast, CC23, including its namesake ST23, has been associated with a wide homeothermic and poikilothermic host range, but never with fish. The aim of this study was to determine whether ST23 is virulent in fish and to identify genomic markers of fish adaptation of S. agalactiae. Intraperitoneal challenge of Nile tilapia, Oreochromis niloticus (Linnaeus), showed that ST260 is lethal at doses down to 102 cfu per fish, whereas ST23 does not cause disease at 107 cfu per fish. Comparison of the genome sequence of ST260 and ST23 with those of strains derived from fish, cattle and humans revealed the presence of genomic elements that are unique to subpopulations of S. agalactiae that have the ability to infect fish (CC7 and CC552). These loci occurred in clusters exhibiting typical signatures of mobile genetic elements. PCR‐based screening of a collection of isolates from multiple host species confirmed the association of selected genes with fish‐derived strains. Several fish‐associated genes encode proteins that potentially provide fitness in the aquatic environment.  相似文献   

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9.
Attempts were made to identify the association between water quality parameters and the presence of Streptococcus agalactiae in cage cultured red hybrid tilapia, Oreochromis niloticus × O. mossambicus. Fish from commercial floating net cage‐culture systems in a river and lake were randomly sampled over a 24‐month period. Swabs from the brains, eyes and kidneys were streaked directly onto blood agar to isolate S. agalactiae. Water temperature, dissolved oxygen, pH, clarity, ammonia, nitrite, sulfide, rate of water flow and depth of water at sampling sites were measured at the same time of fish sampling. The prevalence of fish that were cultured positive to S. agalactiae was significantly higher in lake compared with river. The length and weight of the infected fish were between 9 and 33 cm, and between 20 and 760 g respectively. There was a significant and positive strong correlation between the presence of S. agalactiae and fish mortalities in lake. All water quality parameters showed significant differences between river and lake. However, only water temperature, clarity and pH of lake and the ammonia, temperature and dissolved oxygen in river showed significant correlation with the presence of S. agalactiae in the cultured fish. It was concluded that several unfavourable water quality in the fish farm influencing the presence of S. agalactiae in cultured red hybrid tilapia.  相似文献   

10.
Streptococcus agalactiae causes a severe systemic disease in fish, and the routes of entry are still ill‐defined. To address this issue, two groups of 33 red tilapia Oreochromis spp. each of 10 g were orally infected with S. agalactiae (n = 30), and by immersion (n = 30), six individuals were control‐uninfected fish. Three tilapias were killed at each time point from 30 min to 96 h post‐inoculation (pi); controls were killed at 96 h. Samples from most tissues were examined by haematoxylin–eosin (H&E), indirect immunoperoxidase (IPI) and periodic acid‐Schiff; only intestine from fish infected by gavage was evaluated by transmission electron microscopy. The results of both experiments suggest that the main entry site of S. agalactiae in tilapia is the gastrointestinal epithelium; mucus seems to play an important defensive role, and environmental conditions may be an important predisposing factor for the infection.  相似文献   

11.
Nile tilapia (Oreochromis niloticus) farming is an economic activity that is soaring in the whole world. Septicemia due to Streptococcus agalactiae is the main disease impacting fish farming. The aim of this study was to compare the gut microbiome of healthy animals and animals experimentally infected with S. agalactiae strain 21171A. The microbiome was established with 16S ribosomal DNA next‐generation sequencing (NGS). One hundred Nile tilapias, with an average weight of 35 g, were distributed into two groups. Fifty fish from the challenged group were orally inoculated with 100 μl of a bacterial solution containing 1.98 × 103 CFU/ml of S. agalactiae strain 21171A, while 50 controls were orally inoculated with sterile saline. After the experiment, 24 fish from the challenged group and 27 fish from the control group were analysed. For both groups, bacteria attached to the mucosa (M) and present in faeces (F) were analysed. The mean of the number of taxa identified in the infected group (M + F) (45.87 ± 30.13) was lower than in the control (M + F) (67.70 ± 21.10) (p < .01). Nineteen bacterial taxa were more abundant in faecal samples from the infected group when compared with the control group (p < .01). Thirty‐nine taxa were associated with mucosa samples from the challenged group when compared to the control samples (p < .01). No OTU was associated with healthy samples. The results demonstrate that the infection with S. agalactiae reduces the variability of the gut microbiota. Moreover, some bacteria proliferate during the infection.  相似文献   

12.
In this study, the use of Lactobacillus acidophilus as a probiotic for Nile tilapia (Oreochromis niloticus) culture was studied. Fish survival and the expression of some genes involved in the immune response were assessed. Diet supplementation with L. acidophilus for 15 days caused a significant increase in fish survival during a challenge with Aeromonas hydrophila and variations in immune response related to IL‐1β and transferrin expression in Nile tilapia spleen and kidney. Moreover, extracellular products (ECPs) of L. acidophilus showed high antibacterial activity against fish pathogens such as A. hydrophila and Streptococcus agalactiae in vitro. It was also observed that viable L. acidophilus was able to disrupt quorum sensing activity in Chromobacterium violaceum.  相似文献   

13.
This study evaluated the effects of the probiotic Lactobacillus plantarum as dietary supplement on growth performance, haemato‐immunological responses, microbiology, histology and transmission electron microscopy of the intestinal epithelium of Nile tilapia challenged with Streptococcus agalactiae. Fish were distributed into two groups: control (unsupplemented) group and the group fed L. plantarum supplemented diet for a period of 58 days. We observed an increase in the concentration of lactic acid bacteria and a reduction in the number of Vibrionaceae in supplemented fish. A significant increase in the final weight, specific growth rate and feed efficiency was also observed in supplemented fish. After challenge, the number of thrombocytes and neutrophils also increased in supplemented animals. Transmission electron microscopy showed damage to the intestinal mucosa and the presence of bacteria similar to S. agalactiae in both infected groups. L. plantarum colonized the intestines of fish, enhanced the growth performance and modulated some haematological parameters.  相似文献   

14.
Streptococcosis is an important bacterial disease in Nile tilapia causing severe economic losses to tilapia aquaculture worldwide. The effects of water quality (low‐ [LS] and high‐level [HS] soiling, to mimic clean or dirty surface conditions and temperatures) and disinfectant application (diluted concentrations and exposure time) were characterized on the inactivation of Streptococcus agalactiae isolated from diseased tilapia. Five isolates were tested against three commercial disinfectant products with the main ingredients being povidone iodine (Anidine 100?; AD), benzalkonium chloride (Better BKC 80%?; BKC 80), and a mixture of quaternary ammonium compounds and glutaraldehyde (Chloraldehyde?; CR). CR demonstrated highest efficacy to S. agalactiae inactivation, followed by BKC 80 and AD, respectively. Higher‐level soiling, low temperature, diluted concentrations and short exposure time all decreased the disinfectant efficacy. CR and BKC 80 provided more than 5‐log inactivation at 1‐min exposure at 20°C under HS conditions, and also with ten‐fold‐diluted concentrations at 60‐min exposure time at 30°C. However, AD required 10‐min exposure to effectively remove bacteria under LS conditions at 30°C. The results could facilitate aquaculture management planning that leads to operating cost reductions and improvements in biosecurity.  相似文献   

15.
The effect of different dietary oil sources on the innate immunity and resistance of Nile tilapia, Oreochromis niloticus, to Streptococcus agalactiae infection were evaluated. Fish were fed with diets containing different lipid sources (soybean oil [SO], corn oil, linseed oil [LO], fish oil [FO], and olive oil [OO]). Fish fed SO presented the highest (P < 0.05) hematocrit and serum protein. LO and FO diets increased (P < 0.05) the erythrocyte resistance to osmotic lysis in comparison with other treatments. Fish fed OO showed the highest (P < 0.05) iron‐binding capacity and the lowest serum lysozyme and bactericidal activities (P < 0.05). No difference (P > 0.05) was found between diets in alternative complement activity. Fish fed the SO diet had the highest (P < 0.05) survival rate against S. agalactiae challenge. In conclusion, diets with LO oil and FO, rich in ω‐3 fatty acids, and OO, rich in ω‐9 fatty acids, have an immunomodulatory effect in Nile tilapia juveniles. The use of SO in the Nile tilapia diet improved immune function and resistance against S. agalactiae.  相似文献   

16.
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   

17.
A feeding trial was conducted to investigate the effect of different levels of Bacillus subtilis LT3‐1 in diets on growth, immune parameters, intestinal morphology and disease resistance in genetically improved farmed tilapia, Oreochromis niloticus. Fish (46.91 ± 0.17 g) were fed with a basal diet supplemented with B. subtilis LT3‐1 at 0 (B0), 3.8 × 1010 (B1), 7.6 × 1010 (B2), 1.14 × 1011 (B3) and 1.52 × 1011 (B4) CFU kg?1 for 6 weeks. The results showed that the weight gain of fish in B1 group was significantly enhanced compared to that in B0 group (p < 0.05). The addition of B. subtilis significantly affected serum biochemical indices (total protein, albumin, aspartate aminotransferase, alkaline phosphatase). Besides, the haematocrit, total counts of red and white blood cells, as well as the serum catalase and lysozyme activities, were increased, whereas the serum malondialdehyde, the serum immunoglobulin M and complement three contents were reduced. Parameters for intestinal morphology suggested a healthier intestine for the fish fed B. subtilis‐supplemented diets than fish fed the control diet. The survival rate after Streptococcus agalactiae challenge increased in tilapia fed with B. subtilis. The present study demonstrated B. subtilis can effectively improve growth, immunological status and resistance against S. agalactiae infection in tilapia farming.  相似文献   

18.
Since 2007, 96 wild Queensland groupers, Epinephelus lanceolatus, (Bloch), have been found dead in NE Australia. In some cases, Streptococcus agalactiae (Group B Streptococcus, GBS) was isolated. At present, a GBS isolate from a wild grouper case was employed in experimental challenge trials in hatchery‐reared Queensland grouper by different routes of exposure. Injection resulted in rapid development of clinical signs including bilateral exophthalmia, hyperaemic skin or fins and abnormal swimming. Death occurred in, and GBS was re‐isolated from, 98% fish injected and was detected by PCR in brain, head kidney and spleen from all fish, regardless of challenge dose. Challenge by immersion resulted in lower morbidity with a clear dose response. Whilst infection was established via oral challenge by admixture with feed, no mortality occurred. Histology showed pathology consistent with GBS infection in organs examined from all injected fish, from fish challenged with medium and high doses by immersion, and from high‐dose oral challenge. These experimental challenges demonstrated that GBS isolated from wild Queensland grouper reproduced disease in experimentally challenged fish and resulted in pathology that was consistent with that seen in wild Queensland grouper infected with S. agalactiae.  相似文献   

19.
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   

20.
Streptococcosis, lactococcosis and enterococcosis are among the most important bacterial diseases affecting tilapia farms in Kafr Elsheikh governorate, Egypt. A number of clinically diseased fish were collected and submitted to our laboratory during disease outbreak in 2018. They were characterized by nervous swimming behaviour, skin darkness, exophthalmia, ocular opacity and haemorrhages. Necropsy findings were splenomegaly, congestive hepatomegaly, liquefied brain and enteritis. The phenotypic and molecular characterizations of the bacterial strains isolated from naturally infected fish identified three genera of Gram‐positive cocci: Streptococcus agalactiae, Enterococcus faecalis and Lactococcus garvieae. Infectivity trials were conducted in four groups of Nile tilapia inoculated with S. agalactiae Egy‐1, E. faecalis Egy‐1 and L. garvieae Egy‐1 strains and saline. Mortalities, clinical signs and pathological findings were recorded daily 14 days post infection. Experimentally infected tilapia showed similar clinical signs, postmortem lesions, but varied in the severity and experienced high mortalities up to 70% in case of S. agalactiae and L. garvieae infections and 30% in case of E. faecalis infection. Pathological examination of infected tissue sections stained with modified Brown–Brenn and immunohistochemistry revealed an important direct correlation between the distribution of each bacterial isolate and the lesions developed in different organs. Furthermore, the isolates were subjected to profiling against 11 antibiotics, and they showed resistance against several types of antibiotics, which implicate potential risk to human health and emphasize the urgent need for alternate bio‐control strategies to prevent the diseases and the problem of multidrug resistance in aquatic environment.  相似文献   

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