| Staphylococcus aureus(S.aureus) is a bacterial pathogen of duck which causes ducks acute or chronic diseases. The disease predominantly affects cage-rearing ducks and breeding ducks.The affected ducks are mainly characterized as joint swelling, joint cavity with purulent or serous fibrin exudate, hepatomegaly, splenomegaly necrosis. In recent years, duck staphylococcal infection occurred frequently in duck farms in Shandong province and it caused great economic loss to duck industry. In order to control and prevent the prevalence of duck staphylococcal infection, fifty-six S.aureus strains were isolated and identified in our study. Furthermore, a S.aureus strain was amplified and used to examine the pathogenic to ducks.Bacteria strains were isolated and purified from the collected samples of suspectedly S.aureus infected ducks in Shandong province. S.aureus was initially identified, based on the analysis of its culture characteristics, morphological characteristics and biochemical characteristics. Then, S.aureus is further defined using PCR. Drug sensitivity of isolated strains was tested with drug sensitive slips. The results showed that various isolates were varying degrees of resistance or multi-drug resistance to antibiotics. Cefradine, cefotaxime and minocycline are highly sensitive that can be used as clinical medicine. These results can provide a guide for clinical treatment of anti- S. aureus infecetion.According to the sequences of S. aureus enterotoxin genes and resistance genes published in GenBank database. Seven pairs of primers were designed using Primer Premier 5.0software to examine seven enterotoxin genes and four pairs of primers were designed to examine resistance gene. The results of Amplified enterotoxin genes of 56 isolates showed that the rates of enterotoxin G and B genes were 32.1%, 26.8%, respectively, and they were the highest detection in seven enterotoxin genes. The rates of A gene, C gene and H gene were17.9%, 16.1% and 16.1%, respectively. The rates of D gene and E gene were 12.5% and 8.9%,respectively. The results of amplified antibiotic-resistance genes in 56 isolates of S.aureus showed that the detection rate of mecA-resistance gene was 60.7%(34/56), the detection rate of fem A-resistance gene was 37.5%(21/56), the detection rate of grlA-resistance gene was48.2%(27/56) and the detection rate of norA-resistance gene was 55.4%(31/56). Multi-antibiotic resistance genes were amplified in most S. aureus isolates.The bred ducks were artificially infected S.aureus through the hypodermic inoculation.The clinical symptoms of ducks were observed. Ducks of test group and the control group were randomly sacrificed after inoculation at different times. The pathological changes of various organs were observed. S. aureus were isolated and identified in various tissues and organs. At the same time, liver, spleen, kidney, lung, heart and other tissues were collected and fixed in formalin. The changes of tissues and organs were observed by making a biopsy. The test results showed that the clinical symptoms, the pathological change and the histopathological changes in test group of ducks were similar to duck S.aureus disease reported abroad. The ducks of test group by necropsied found that the subcutaneous of thoracic and abdominal hyperemia, hemorrhage, have jelly-like edema fluid, hepatomegaly, splenomegaly, lung hemorrhage, edema, kidney enlargement, drake testicular swelling, bleeding. The ducks of control group by necropsied had no significant lesions. The bacteria which isolated from ducks in the test group were identical with the bacteria by inoculated in morphological characteristics after the identification. The bacteria has different the separation rate in different tissues and organs. The separation rate of joint was highest. The main feature of the histopathological changes were: the liver steatosis, hepatocellular necrosis, lymphocytes significant reduction in spleen, spleen necrosis, kidney degeneration, renal tubular epithelial cells necrosis. |
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