摘要
近年来，由嗜麦芽寡养单胞菌(Stenotrophomonas maltophilia，Sma)引发的斑点叉尾鮰(Ictalurus Punctatus)的急性、流行性传染病给我国斑点叉尾鮰养殖业造成了严重的影响。该病以体表出现圆形、椭圆形或不规则的褪色斑，腹水、肠炎和肠套叠为病变特征。但目前对该病的致病机理还不清楚，本试验对斑点叉尾鮰源嗜麦芽寡养单胞菌的胞外产物(extracellular products，ECP)的活性成分和致病性进行了研究，其目的在于搞清Sma ECP的活性，以及ECP对小白鼠和斑点叉尾鮰的致病性和病理损伤作用，从而为阐明该病的致病机理提供理论资料。
试验采用平板扩散法对斑点叉尾鮰源Sma ECP活性进行了测定，结果表明该菌ECP具有蛋白酶、脂酶、脲酶、明胶酶活性和溶血毒性，而不具备淀粉酶和卵磷脂酶活性。采用家兔肠袢试验和乳鼠灌胃试验表明Sma ECP具有肠毒性；Sma ECP接种Vero细胞后表现出明显的细胞病变，表明其具有明显的细胞毒性。
Sma ECP对小白鼠的致病性试验表明：Sma ECP对小白鼠具有明显的致病性，其LD_(50)为5.37mg／kg。接种小鼠主要表现为呼吸困难，食欲减退，排黄色粘液；肺淤血、出血，肠道扩张、壁变薄，肠腔内充有大量气体和一定的黏液。病理组织学上，肺泡壁毛细血管扩张淤血，肺泡腔内充斥大量红细胞，呼吸上皮肿胀、坏死、脱落；肺支气管上皮脱落；肠粘膜上皮坏死、脱落，固有膜与黏膜下层水肿、大量炎症细胞浸润；肝细胞空泡变性、坏死；脾出血，淋巴细胞数量明显减少。
Sma ECP对斑点叉尾鮰的致病性试验表明：Sma ECP对斑点叉尾鮰具有明显的致病性，其LD_(50)为3.21mg／kg。接种鱼主要表现为鳍条基部充血、出血，体表褪色斑，腹部膨大，腹腔内充有大量淡黄色或带血的腹水，胃肠道炎症，肠道套叠，肠腔内充满淡黄色或含血的粘液。病理组织学上表现为肝水肿，狄氏间隙显著增宽，肝细胞轻微空泡变性；脾出血、坏死；肾间质水肿，造血拟淋巴组织坏死，巨噬细胞和淋巴细胞浸润，肾小管上皮颗粒变性甚至坏死，肾小球肿大，毛细血管扩张充血，肾小囊挤压缩小甚至消失；胃肠道粘膜上皮变性、坏死，脱落，固有膜，粘膜下层水肿，炎症细胞浸润；骨骼肌变性、坏死，大量嗜中性白细胞和巨噬细胞浸润。细胞病理学上，病鱼主要器官的细胞均有较为严重的损伤，细胞肿胀，超微结构破坏，特别是细胞核的损伤很明显。细胞核变形、染色质溶解或发生浓缩、裂解边移；线粒体表现为肿胀，嵴断裂，断裂或溶解消失，呈空囊状。
Recently, The Stenotrophomonas maltophilia from Channel Catfish was detected as the pathogen of a acute epidemic of channel catfish(Ictalurus Punctatus) in China. The pathology of charmel catfish infected by Stenotrophomonas maltophilia showed many typical characters, like many irregular, variably sized areas of bianch in the body surface, distension of abdomen, enteritis and intussusceptions etc. However, the pathogenic mechanism of Stenotrophomonas maltophilia infection was unclear. The aim of this investigation was to make the biochemical activity of extracellular products clear, and to understand the pathogenicity of extracellular products to rice and channel catfish.
The biologic activities of Stenotrophomonas maltophilia extracellular products were studied. The results showed that the extracellular products include amylase, lipase, protease, urease, haemlysin, cytotoxicity and cell toxicity.
The pathology of mice infected with Stenotrophomonas maltophilia's extracellular products was studied by clinical and histopathology examination. The extracellular products displayed lethality to mice, with a LD_(50) value of 5.37mg/kg。The main symptom was anhelation, mucous cenosis, lungs hemorrhages, dilatation and tenuate of the intestinal wall, massive mucous in the cavum intestinale. Histopathologieal examination showed blood capillary congested, the epithelium of pulmonary alveolus happened necrosis and exfoliation, lung accent appeared extravasated blood in lungs; epithelium of intestines happened necrosis, abscission; Vacuolar degeneration appeared in liver; cells of white pulp in spleen reduced, and red pulp appeared hemorrhage in spleen.
The pathology of channel catfish infected with Stenotrophomonas maltophilia's extracellular products was studied by clinical, histopathology and microscope examination. The extracellular products displayed lethality to channel catfish, with a LD_(50) value of 3.21 mg/kg。The main symptom showed that congestion and hemorrhage in the root of fins, and many irregular, variably sized areas of bianch in the body surface, distension of abdomen, and there may be bloody mucus and fluid in the cavum abdominis, enteritis and intussusceptions, hemorrhage in mucus of intestinal tract. Histopathological examination showed revealed that edema, vacuolar degeneration, even necrosis in live; hyperaemia, intumesce in glomcrulus; granular degeneration and vacuolar degeneration in the epithelia of nephric tubule; lymphocyte induced and hemorrhaged in spleen; swelling and necrosis in gill lamella epithelia; necrotizing myositis in skeletal muscles. Cytopathological changes showed that swelling and ultrastructure destory in visceral organs' cells. The chromatin showed condensation and margination. The mitochondria swelled with disintegration and lyses of the cristaes.
引文
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