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1.
Flavobacterium psychrophilum is responsible for significant economic losses in rainbow trout aquaculture. Antimicrobial treatment remains the primary means of control; however, there are limited choices available for use. The objectives of the study were therefore to determine the minimum inhibitory concentrations for erythromycin and florfenicol in selected F. psychrophilum isolates and to evaluate their clinical treatment efficacy in experimentally infected rainbow trout. All isolates tested had moderate susceptibility to florfenicol and erythromycin except one isolate, which had low susceptibility to erythromycin. Two isolates (one with moderate and one with low susceptibility to erythromycin) were used in an experimental infection trial. Rainbow trout juveniles were injected intraperitoneally with 108 cfu/fish and after mortality had begun, fish were given erythromycin‐ and florfenicol‐medicated feed at a rate of 75 mg kg?1 day?1 and 10 mg kg?1 day?1 fish body weight, respectively, for 10 consecutive days. The splenic F. psychrophilum load was determined using an rpoC quantitative PCR throughout the 30‐day trial. Relative to antibiotic‐free controls, erythromycin treatment significantly (p < 0.05) reduced mortality of rainbow trout juveniles infected with FPG101, even when treatment was initiated after clinical signs developed.  相似文献   

2.
Control methods for Flavobacterium psychrophilum are limited and oftentimes ineffective; hence, research efforts have focused on vaccine development. This study tested the hypothesis that a crude lipopolysaccharide (LPS) extract from F. psychrophilum will elicit a protective immune response in rainbow trout Oncorhynchus mykiss (Walbaum) against F. psychrophilum challenge. Rainbow trout (mean weight, 3 g) were immunized intraperitoneally with the following treatment and control preparations: 10 μg of crude LPS with or without Freund's complete adjuvant (FCA), 25 μg of crude LPS with or without FCA and saline with or without FCA. Immunization of fish with 10 or 25 μg of crude LPS/FCA resulted in significant antibody responses against F. psychrophilum using ELISA with a whole‐cell lysate as the coating antigen, but only minimal levels of protection were conferred following F. psychrophilum challenge at 14 weeks post immunization. Western blot analyses demonstrated that fish exhibited antibodies specific for low‐molecular mass proteins present in the crude LPS extract, but did not exhibit antibodies specific for F. psychrophilum LPS. The results indicate that higher immunization doses and/or the use of an alternative extraction method that yields larger LPS molecules (23–70 kDa) may be necessary to elicit specific antibody responses against F. psychrophilum LPS.  相似文献   

3.
Bacterial coldwater disease, caused by Flavobacterium psychrophilum, remains one of the most significant bacterial diseases of salmonids worldwide. A previously developed and reported live‐attenuated immersion vaccine (F. psychrophilum; B.17‐ILM) has been shown to confer significant protection to salmonids. To further characterize this vaccine, a series of experiments were carried out to determine the cross‐protective efficacy of this B.17‐ILM vaccine against 9 F. psychrophilum isolates (representing seven sequence types/three clonal complexes as determined by multilocus sequence typing) in comparison with a wild‐type virulent strain, CSF‐259‐93. To assess protection, 28‐day experimental challenges of rainbow trout (Oncorhynchus mykiss) fry were conducted following immersion vaccinations with the B.17‐ILM vaccine. F. psychrophilum strains used in challenge trials were isolated from several fish species across the globe; however, all were found to be virulent in rainbow trout. The B.17‐ILM vaccine provided significant protection against all strains, with relative percent survival values ranging from 51% to 72%. All vaccinated fish developed an adaptive immune response (as measured by F. psychrophilum‐specific antibodies) that increased out to the time of challenge (8 weeks postimmunization). Previous studies have confirmed that antibody plays an important role in protection against F. psychrophilum challenge; therefore, specific antibodies to the B.17‐ILM vaccine strain appear to contribute to the cross‐protection observed to heterologous strain. The ability of such antibodies to bind to similar antigenic regions for all strains was confirmed by western blot analyses. Results presented here support the practical application of this live‐attenuated vaccine, and suggest that it will be efficacious even in aquaculture operations affected by diverse strains of F. psychrophilum.  相似文献   

4.
The immune response in rainbow trout fry against Flavobacterium psychrophilum was elucidated using an immersion‐based challenge with or without prior exposure to hydrogen peroxide (H2O2). Samples were taken from the head kidney 4, 48, 125 and 192 h after immersion, and the regulation of several genes was examined. Bacterial load was assessed based on the presence of 16S rRNA and correlated with gene expression, and the levels of specific antibodies in the blood were measured 50 days post‐infection. Separately, both H2O2 and F. psychrophilum influenced gene expression, and pre‐treatment with H2O2 influenced the response to infection with F. psychrophilum. Pre‐treatment with H2O2 also affected correlation between gene regulation and pathogen load for several genes. A delay in antibody production in H2O2‐treated fish in the early phase of infection was indicated, but H2O2 exposure did not affect antibody levels 50 days post‐infection. An increasing amount of F. psychrophilum 16S rRNA was found in the head kidneys of infected fish pre‐treated with H2O2 relative to the F. psychrophilum group. The results show that a single pre‐treatment with H2O2 impairs the response against F. psychrophilum and may intensify infection.  相似文献   

5.
Co‐infection of rainbow trout with infections haematopoietic necrosis virus (IHNV) and Flavobacterium psychrophilum is known to occur, and it has been speculated that a combined infection can result in dramatic losses. Both pathogens can persist in fish in an asymptomatic carrier state, but the impact of co‐infection has not been well characterized or documented. In this study, it was hypothesized that fish co‐infected with F. psychrophilum and IHNV would exhibit greater mortality than fish infected with either pathogen alone. To test this, juvenile rainbow trout were co‐infected with low doses of either IHNV or F. psychrophilum, and at 2 days post‐initial challenge, they were given a low dose of the reciprocal pathogen. This combined infection caused high mortality (76.2%–100%), while mortality from a single pathogen infection with the same respective dose was low (5%–20%). The onset of mortality was earlier in the co‐infected group (3–4 days) when compared with fish infected with F. psychrophilum alone (6 days) or IHNV (5 days), confirming the synergistic interaction between both pathogens. Co‐infection led to a significant increase in the number of F. psychrophilum colony‐forming units and IHNV plaque‐forming units within tissues. This finding confirms that when present together in co‐infected fish, both pathogens are more efficiently recovered from tissues. Furthermore, pathogen genes were significantly increased in co‐infected groups, which parallel the findings of increased systemic pathogen load. Extensive tissue necrosis and abundant pathogen present intracellularly and extracellularly in haematopoietic tissue. This was pronounced in co‐infected fish and likely contributed to the exacerbated clinical signs and higher mortality. This study provides novel insight into host–pathogen interactions related to co‐infection by aquatic bacterial and viral pathogens and supports our hypothesis. Such findings confirm that mortality in fish exposed to both pathogens is greatly elevated compared to a single pathogen infection.  相似文献   

6.
Tenma  Hinako  Tsunekawa  Koki  Fujiyoshi  Riho  Takai  Hajime  Hirose  Masae  Masai  Nanami  Sumi  Kosuke  Takihana  Yuta  Yanagisawa  Sogen  Tsuchida  Kota  Ohara  Kenichi  Jo  Toshiaki  Takagi  Masaki  Ota  Akiko  Iwata  Hiroyoshi  Yaoi  Yuichi  Minamoto  Toshifumi 《Fisheries Science》2021,87(3):321-330

Outbreaks of bacterial cold-water disease (BCWD), caused by Flavobacterium psychrophilum, are widespread in Japan, especially among ayu Plecoglossus altivelis. There are few investigations of F. psychrophilum in river water, and its seasonal distribution has not been clarified. We aimed to identify the spatiotemporal dynamics of F. psychrophilum and ayu to provide information that is useful for establishing a countermeasure for BCWD. Quantitative analysis of environmental DNA (eDNA) was used to clarify the year-round dynamics of ayu and F. psychrophilum. We sampled river water from the Nagara and Ibi rivers in Japan, and conducted monthly water sampling and eDNA quantification. Changes in the eDNA concentration of ayu were consistent with the known life histories of the fish. There was a strong negative correlation between the eDNA concentration of F. psychrophilum and water temperature, suggesting a strong dependence of F. psychrophilum dynamics in the river on water temperature. Furthermore, relatively high eDNA concentrations were recorded for both organisms in early summer and fall, suggesting that ayu is infected with F. psychrophilum during these seasons when experiencing up- and downmigration, respectively.

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7.
The disease outbreaks in aquaculture system of wetlands are the major cause of fish mortality. Among various bacterial septicaemic diseases, fish mortality caused by Acinetobacter spp. is recently reported in different fish species. Fish disease outbreak was investigated in a wetland of West Bengal, India to identify the aetiological factors involved. The moribund fish were examined and subjected to bacterial isolation. Two bacterial causative agents were identified as Acinetobacter junii and Acinetobacter pittii by biochemical characterization and 16S rRNA gene amplification. Both the isolates were oxidase‐negative, nitrate‐negative, catalase‐positive and indole‐negative. The molecular identification using 16S rRNA gene sequencing and phylogenetic tree analysis further confirmed the two Acinetobacter spp. with 97%–99% similarity. The antibiotic resistance patterns of these two bacteria revealed that both of them were resistant to β‐lactam, cefalexin, cephalothin, amoxyclav, cefuroxime, cefadroxil, clindamycin, vancomycin and penicillin. In addition, A. pittii was also resistant to other antibiotics of cephams group such as ceftazidime and cefotaxime. In the challenge experiment, both A. junii and A. pittii were found to be pathogenic with LD50 of 1.24 × 105 and 1.88 × 107 cfu/fish respectively. Histopathological examination of gill, liver and kidney revealed prominent changes supporting bacterial septicaemia. The investigation reports for the first time on concurrent infection by A. junii and multidrug‐resistant (MDR)‐A. pittii as emerging fish pathogens to cause severe mortality in Labeo catla and Hypophthalmichthys molitrix in a freshwater wetland.  相似文献   

8.
The Gram‐negative bacterium, Flavobacterium psychrophilum, is endemic to California, USA, where it is an important pathogen in salmonid aquaculture, especially in rainbow trout (Oncorhynchus mykiss). Disease outbreaks caused by F. psychrophilum in rainbow trout fingerlings can approach 90% mortality, resulting in millions of dollars of economic losses annually. The focus of this study was to investigate the genetic diversity of 49 F. psychrophilum isolates collected from disease outbreaks in 17 salmonid hatcheries in California, USA, from 2015 to 2018 using multilocus sequence typing. Results suggest California F. psychrophilum isolates are diverse, representing 11 distinct sequence types (STs), three of which were previously undescribed. Still, the majority of genotyped isolates (n = 41) belonged to a single clonal complex (CC), CC‐ST10, which is the largest CC worldwide and has been linked to disease outbreaks on several continents. Results of this study provide evidence of marked intraspecific genetic diversity of F. psychrophilum from California. The biological significance of this genetic variability is unclear but could have implications for future vaccine development and treatments. Further studies investigating the virulence, antigenic, and antimicrobial susceptibility profiles of F. psychrophilum are warranted to better understand the epizootiology of this pathogen in the Western United States.  相似文献   

9.
A previous proteomic study examining the plasma acute‐phase response of rainbow trout to sterile inflammation highlighted an unidentified 9.5‐kDa spot using 2D‐PAGE, which was dramatically increased. The 15 amino acid sequence obtained from this protein spot allowed rapid amplification of cDNA ends PCR to generate a 443‐bp nucleotide sequence that was 98.6% similar to type‐4 ice‐structuring protein LS‐12 from Atlantic salmon Salmo salar Linnaeus. Quantitative reverse translation PCR and an ELISA were used to measure gene expression and plasma concentrations of LS‐12 following experimental intraperitoneal injection of rainbow trout with either 106 or 108 colony‐forming units (CFU) of Flavobacterium psychrophilum. There was no significant change in the plasma concentration of LS‐12 up to 15 days post‐infection in any group. Hepatic LS‐12 gene expression was significantly reduced at 3 and 6 days (p < 0.001) post‐infection in fish injected with 108 CFU of F. psychrophilum relative to control fish, while branchial or head kidney expression was unchanged. Infected fish had significantly increased hepatic gene expression of serum amyloid A, confirming an acute‐phase response. Under the conditions used, LS‐12 is not a positive acute‐phase protein in rainbow trout.  相似文献   

10.
为确定患病虹鳟的病原,本实验从患病鱼溃烂肌肉中分离到2株细菌,分别命名为CH06和CH07,经回归感染证实分离菌株为导致此次虹鳟患病的病原菌,并进一步对其形态特征、理化特性、分子特征、血清型及耐药性进行分析。结果显示,CH06和CH07株在TYES琼脂平板上呈煎蛋状外观,产黄色素,氧化酶和过氧化氢酶呈阳性,能水解明胶和酪蛋白,不能水解淀粉,不能利用果糖、半乳糖和七叶苷等。16S rRNA比对结果显示,CH06和CH07株与嗜冷黄杆菌模式株NBRC 15942的同源性分别为99.35%和99.42%。综合菌株理化和分子特性确定CH06和CH07株为嗜冷黄杆菌。利用多重PCR方法鉴定CH06和CH07株的血清型均为1型(Fd型);多位点序列分型(MLST)分析表明,CH06和CH07株的基因型分别为ST-12和ST-78型,且均属于CC-ST10克隆型。人工感染结果显示,CH06和CH07株对虹鳟幼鱼具有较高致病性,其半致死浓度(LD50)分别为7.1×105和1.1×105 CFU/mL,攻毒剂量与临床病症出现时间呈反比,从人工感染实验鱼的肌肉、脾脏等组织中可重新分离到嗜冷黄杆菌。组织病理变化显示,病鱼肝细胞肿胀,空泡变性,部分肝细胞溶解坏死,细胞核溶解消失;脾脏充血、出血,淋巴细胞减少,红细胞和含铁血黄素增多;肌纤维间隙增宽、断裂、弯曲不齐,部分肌细胞肌浆溶解呈蜂窝状。CH06和CH07株对10种抗菌药物的耐药谱略有不同,均对氨苄西林和甲氧苄啶-磺胺甲噁唑敏感;CH06株对恩诺沙星、氟苯尼考等耐药,而CH07株对恩诺沙星和氟苯尼考中度敏感。本研究首次报道了我国虹鳟源嗜冷黄杆菌的分离鉴定及生物学特性,以期为虹鳟细菌性冷水病的防控提供科学依据。  相似文献   

11.
Diets containing deoxynivalenol (DON) were fed to rainbow trout Oncorhynchus mykiss (Walbaum) for 4 weeks followed by experimental infection (intraperitoneal) with Flavobacterium psychrophilum (4.1 × 106 colony‐forming units [CFU] mL−1). Mortality of rainbow trout fed either 6.4 mg kg−1 DON or trout pair‐fed the control diet was significantly reduced (P < 0.05) in comparison with trout fed the control diet to apparent satiation (<0.1 mg kg−1 DON). In a second experiment, trout were fed one of three experimental diets; a control diet, a diet produced with corn naturally contaminated with DON (3.3 mg kg−1 DON) or a diet containing purified DON (3.8 mg kg−1); however, these fish were not experimentally infected. The presence of DON resulted in significant reduction (P < 0.0001) in feed intake as well as weight gain after 4 weeks. Respiratory burst of head‐kidney leucocytes isolated from rainbow trout fed diets containing purified DON (3.8 mg kg−1) was significantly higher (P < 0.05) at 35 day post‐exposure compared with controls. The antimicrobial activity of DON was examined by subjecting F. psychrophilum in vitro to serial dilutions of the chemical. Complete inhibition occurred at a concentration of 75 mg L−1 DON, but no effect was observed below this concentration (0–30 mg L−1).  相似文献   

12.
Routine application of antimicrobials is the current treatment of choice for rainbow trout fry syndrome (RTFS) or bacterial coldwater disease (BCWD) caused by Flavobacterium psychrophilum. In this study, the antimicrobial susceptibilities of 133 F. psychrophilum isolates, 118 of which were from the UK, were evaluated by broth microdilution and disc diffusion methods following VET04‐A2 and VET03‐A guidelines of Clinical and Laboratory Standards Institute (CLSI), respectively. Isolates were categorized as wild type (fully susceptible, WT) or non‐wild type (NWT) using normalized resistance interpretation (NRI)‐determined cut‐off values (COWT). Broth microdilution testing showed that only 12% of UK isolates were WT to oxolinic acid (MIC COWT ≤ 0.25 mg/L) and 42% were WT for oxytetracycline (MIC COWT ≤ 0.25 mg/L). In contrast, all the isolates tested were WT (MIC COWT ≤ 2 mg/L) for florfenicol, the main antimicrobial for RTFS control in the UK. Disc diffusion‐based COWT values were ≥51 mm for 10 μg amoxicillin, ≥44 mm for 30 μg florfenicol, ≥30 mm for 2 μg oxolinic acid and ≥51 mm for 30 μg oxytetracycline. There was a high categorical agreement between the classifications of the isolates by two testing methods for florfenicol (100%), oxytetracycline (93%) and oxolinic acid (99%).  相似文献   

13.
The immune response and morphological changes in the gills of rainbow trout fry after immersion in hydrogen peroxide (H2O2), Flavobacterium psychrophilum or combined exposure were examined. The gills were sampled 4, 48, 125 and 192 h after exposure, and the regulation of expression of the following genes was investigated using qPCR: IgT, IgM, CD8, CD4, MHC I, MHC II, IL-4/13A, TcR-β, IL-10, IL-1β, IL-17, SAA and FoxP3. Bacteria were not observed in haematoxylin-and-eosin-stained gill tissue, but the presence of F. psychrophilum 16S rRNA was detected using qPCR. The 16S rRNA levels were correlated with gene expression. Although pretreatment with H2O2 before immersion in F. psychrophilum did not significantly alter the amount of bacteria found in the gill, the immune response was influenced: exposure to F. psychrophilum resulted in a negative correlation with expression of IL-17c1, MHC I and MHC II, while pretreatment with H2O2 resulted in a positive correlation with IL-4/13A and IgM. Exposure to either H2O2 or F. psychrophilum influenced the regulation of gene expression and damaged tissue. Exposure to both combined altered the immune response to infection and postponed healing of gill tissue.  相似文献   

14.
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   

15.
In this study, 318 bacterial strains were isolated from the gastrointestinal (GI) tracts of 29 rainbow trout, Oncorhynchus mykiss (Walbaum). These bacteria were screened in vitro for their ability to inhibit growth of Flavobacterium psychrophilum, the causative agent of coldwater disease. Bacteria observed to inhibit F. psychrophilum growth were further screened against rainbow trout bile, as an indicator of their ability to survive in the GI tract. This screening resulted in narrowing the pool to 24 bacterial isolates. Those 24 isolates were then tested for pathogenicity in rainbow trout by intraperitoneal injection. Following a 28‐day challenge, eight isolates were shown to cause direct mortality and were eliminated from further study. As a result, 16 bacterial isolates were identified as probiotic candidates with the potential to control or reduce disease caused by F. psychrophilum.  相似文献   

16.
Effects of Bacillus cereus BC‐01, Lactobacillus acidophilus LAG01, Clostridium butyricum CBG01 and their combinations as supplementation on the growth performance, digestive enzyme activities and serum non‐specific immunity of hybrid grouper (Epinephelus lanceolatus ♂×E. fuscoguttatus ♀) were assessed. Seven different diets, that is one control diet (basal feed without any probiotics, CT) and six treatment diets containing single B. cereus (Bs), L. acidophilus (Ls) and C. butyricum (Cs) at 1.0 × 109 cfu/kg feed, and also their combinations in equal proportion at 1.0, 2.0 and 3.0 × 109 cfu/kg feed (BLC1, BLC2 and BLC3) were prepared respectively. After 60‐day feeding trial, the final weight, specific growth rate,food consumption, food conversion efficiency and apparent digestibility coefficient of fish in Ls and BLC3 were significantly higher compared with the control (p < .05). The activities of pepsin and trypsin in the intestine of fish for Ls and BLC3 were significantly higher relative to the control (p < .05). Relative to controls, significantly enhanced amylase and lipase activities in proximal intestine except for Cs and BLC1 and lipase activities in distal intestine except for Cs were observed (p < .05). Meanwhile, activities of superoxide dismutase in the serum of fish for all treatments, lysozyme and catalase in Ls and BLC3, and glutathione peroxidase except for Cs were significantly enhanced (p < .05). Based on the above, dietary supplementation of single L. acidophilus at 1.0 × 109 cfu/kg or combination of three strains at 3.0 × 109 cfu/kg for hybrid grouper is recommended.  相似文献   

17.
The objective of this study was to determine if deoxynivalenol (DON) exposure alters the susceptibility of rainbow trout to bacterial coldwater disease caused by Flavobacterium psychrophilum. Rainbow trout were fed a nutritionally complete diet containing corn that was naturally contaminated with DON at a desired concentration of <0.5 (control and pair‐fed treatments), 4 or 6 ppm over 7 weeks to apparent satiation. After 4 weeks, fish were infected by intraperitoneal injection with F. psychrophilum (3.03x106 CFU mL?1) via intraperitoneal injection and monitored for morbidity and mortality. A significant linear reduction in feed intake was associated with increasing dietary levels of DON contamination over the initial 4 weeks. There was a significant reduction (P < 0.05) in cumulative per cent mortality in DON‐fed groups (4.1 ppm, 11%; 5.9 ppm, 7%) in comparison to control (46%) and pair‐fed (25%) groups at 21 days post infection. Mortality of trout pair‐fed the control diet was also significantly lower (P < 0.05) than the control group fed to apparent satiation. A replicate trial using genetically similar fish and the same experimental design produced similar results. These results suggest that DON exposure and restricted feed intake provided a protective effect for rainbow trout infected with F. psychrophilum.  相似文献   

18.
The study investigated effect of dietary supplementation with malic acid, Bacillus subtilis and a mixture of the two (3 × 2 factorial trial) on Nile tilapia (Oreochromis niloticus) health. Treatment groups (T1–T6) were fed diets containing three levels of malic acid (0.0, 5.0 and 10.0 g/kg), each of which was supplemented with 0 and 1.1 × 105 cfu/g B. subtilis, respectively. Each treatment group was assigned randomly to triplicate groups of 35 fish (5.26 ± 0.06 g) in 18 tanks for 84 days. The results indicated that survival was higher in all dietary treatments as compared to the control fed fish. The highest values of FBW, WG and SGR (%), PER, PPV and ER were recorded in groups T4 and T6, which were fed diets supplemented with 5 g malic acid/kg and 1.1 × 105 cfu/g B. subtilis and 10 g malic acid/kg and 1.1 × 105 cfu/g B. subtilis, respectively. The best value of FCR was obtained in groups T4 and T6. The lowest total bacterial count in the gut and faeces was detected in fish from group T6. The values of haematocrit, haemoglobin, red blood cells, white blood cells, total protein, albumin and globulin were significantly higher (p < .05) in fish from groups T4 and T6 (diets supplemented with malic acid and B. subtilis). As compared to the control fed fish, te mixture of these substances are promising as immune enhancher in aquacultured fish.  相似文献   

19.
Rainbow trout from 23 families were evaluated for growth and resistance to the bacterial coldwater disease (BCWD) caused by Flavobacterium psychrophilum and infectious haematopoietic necrosis (IHN) caused by IHN virus. Average family weights were between 161 and 263 g with an average of 225 g at 213 days post‐fertilization with specific growth rates ranging from 2.37 to 2.88. Per cent survival of fish challenged with F. psychrophilum was between 18% and 100%, while for those challenged with IHNV, the range was between 12% and 93%. Significant positive correlations were found for end body weight and resistance to IHN (P < 0.05) and for early body weight and resistance to BCWD (P < 0.1). However, no significant correlations were detected between resistance to both pathogens or disease resistance and overall genetic diversity or diversity within the major histocompatibility locus.  相似文献   

20.
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