Virulence And Pathogenesis Of Enterococcus Isolates From Ducks

Four strains of Enterococcus isolated from dying ducks clinically in Beijing and Hubei province in 2000～2004 and one reference strain of E. facials obtained from China Institute of Veterinary Drug Control were identified. Experimental infections were performed on laboratory mice and ducks. Furthermore, the profiles of cell wall proteins extracted from different strains were compared by SDS-PAGE and Western-blot analysis, so as to verify if there was some correlation between the cell wall proteins of different strains Enterococcus and their virulence, which would offer some reference for further research on the pathogenesis and immunology mechanisms of Enterococcus.1. The morphological, cultural characters, biochemistry characters and the sensitivity to 10 antimicrobic agents were evaluated to identify the isolates. In results, the bacteria shared following characteristics: gram-positive cocci, arrayed by chain, can grow at 10 ℃, 45℃ and 6.5% NaCl broth, fermentation of sucrose and other biochemistry characters. Most of these biological characters correspond with E. facials. Additionally, the data of drug Sensitivity tests indicated that the sensitive extent of different strains to the antimicrobial agents varied obviously. In conclusion, all the five strains were sensitive to penicillin, vancomycin and gentamycin, but resistant to tetracycline.2. In order to compare the virulence of different strains of Enterococcus, in the present study, 60 ducks and 300 mice were used to inocculated experimentally with different strains. Furthermore, the clinical signs and pathological changes of the experimental animals were observed after the inoculation. Additionally, the morbidity, mortality, bacteria reisolation rate from organs and blood and the 50% lethal dose (LD₅₀) of different strains to mice were determined, respectively. The results indicated that these strains were of differing virulence. Beijing strain was of the highest virulence and the reference strain was of the lowest. Main clinical signs of the experimental ducks include emaciation, production of slimy, waterly and green droppings, swollen of hock and toe joints, lamennes, necrosis and hemorrhage in livers, pericardiac hydrocele, fibrinous pericarditis. The bacteria could be reisolated from liver, cloaca and other organs of the ducks. However, the clinical signs of Beijing strain appeared earlier and more obvious than the other strains. The pathological changes were more serious, too. And the morbidity (100%), mortality (50%) and bacteria reisolation rate (26/30) in experimental ducks was higher, and the LD₅₀ of Beijing strain to the laboratory mice was lower than the other strains.3. In order to analyse the correlation between the cell wall proteins of different strains and their virulence more depth, SDS-PAGE was performed on the cell wall proteins of the 5 experimental strains. Moreover, for Western-blot analysis, the antigen proteins separated by SDS-PAGE were electroblotted onto a immobiolonpolyvinyliden fluorid membrane using the semi-dry blotting system. Blotted proteins were subsequently probed with sera of rabbits pre-immuned with Beijing strain. The result showed that all of...