| It has been well recognized that ETEC was the major pathogenic Escherichia coli that caused piglet diarrheal in pig farm .A polymerse chain reaction (PCR) technology was developed to detect ETEC K88 and its variants (ab, ac, ad). The presence of the K88 and its variants (ab, ac and ad) in some pig farms around Wuhan were investigated by PCR methology, and the K88ac was confirmed the predominant variants in Wuhan area. Through the research of ETEC K88ac cultivation, fimbriae extraction, immune reponse and egg-yolk processing character. An appropriated way of producing anti-K88ac fimbriae egg-yolk antibodies was established. The active mechanism and efficiency of egg yolk antibodies was evaluated by in vivo and in vitro experiments. The results were as follows:1. A polymerse chain reaction (PCR) technology to detect ETEC K88 and its variants (ab, ac, ad) was developed to investigate the presence of the K88 and its variants (ab, ac and ad) in some pig farms around Wuhan. K88ab, K88ac and K88ad by PCR with special primers showed target bands. One of 291 E. coli, which were not deteced K88 by slide agglutination, were checked out to be K88 (K88ac) by PCR. 23(10.1%) K88 were found in 227 feces from diarrheic piglets in some pig farms of Wuhan area, and all contained genes for K88ac. The result suggested that the PCR methodology be a quick, sensitive and specific for the detection and epidemiological investigation of ETEC K88 and its variants (ab, ac, ad). K88ac is the predominant K88 variant associate with diarrhea in piglets of Wuhan area.2. The effect of shaking cultivation and resting cultivation on the production of ETEC K88ac and its fimbriae was compared. An appropriated method of separating-purifying K88ac fimbrial was developed and the immune response of ETEC K88ac fimbriae to hens was studied. A feasible processing of egg yolk antibodies powders was established and its stability and storage performance were also studied. The result suggested that the output of ETEC K88ac with shaking cultivation be about once more than that of resting cultivation. Fimbrial MRHA titer of shaking cultivation and resting cultivation were 26 and 25 respectively. The extraction of ETEC K88ac fimbriae, separated and purified by 60 ℃-heating-magnetism-stir and isoelectric point deposition was 1.5mg/L. The purified fimbriae showed one band in SDS-PAGE with a molecular mass of about 28 KDa. Titerof egg-yolk antibodies rose quickly in a week after the second immune and achieved the top at the 4th week (1:2560), then fell slowly at the 13th week. The results confirmed that shaking cultivation of K88ac with TSB, separating-purifying fimbriae 60℃-heating-magnetism-stir and isoelectric point deposition was a suitable way for the extration of ETEC K88ac fimbriae in the laboratory or on the small scale. Activity of egg-yolk antibodies was not inflenced by spray drying. liter of egg-yolk antibodies did not change with the treatment of 90℃ wet-hot for 5 minutes, but declined 75% for 15 minutes and 50% with the treatment of 90℃ hot-air for 5 minutes; 90℃ wet-hot or hot-air treatment for 1 hour would inactive the antibodies. The antibodies would not be destroyed under the 4℃ and normal atmospheric temperature in half a year. The results suggested that the spray drying be a suitable processing for egg yolk antibodies powders. The egg yolk antibodies powders had good processing stability and storage performance.3. The active mechanism and efficiency of egg yolk antibodies was evaluated by in vivo and vitro experiments. The results suggested that the average numbers of adherent bacterial cells per enteroepithelial cell for control without antibodies was 16.4, the egg-yolk anti-K88ac fimbrial antibodies with liter 1:640 (8.5 bacterial cells per epithelial cell) and 1:1280 (2.4 bacterial cells per epithelial cell) could significantly inhabited the adhesion of ETEC K88ac to piglet epithelial cell (p<0.01) ; Antibodies with titer 1:320 had no significant effect on the adhesion of ETEC K88ac (p>0.05) .90 28-32-days-old piglets...
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