| Diarrhea is the major infectious disease which causes the death of post-weaning piglets, and leads great losses to swine production. The enterotoxigenic E. coli F18 (ECF18) is the major pathogen which induces post-weaning diarrhea. At present, the hereditary basis and regulative mechanism of anti-E. coli F18 are unknown in Chinese native breeds post-weaning piglets, and the resistance genes and genetic mechanism of E. coli F18 between native pig breeds and exotic pig breeds might be different. Gene chip and high-throughput sequencing technology provide a powerful means for screening candidate genes of E. coli F18, and the experiment premise is to obtain E. coli F18-resistant and-sensitive full sibs piglets. Therefore, the selection and identification of local breeds which are resistant/sensitive to E. coli F18 have become the key and bottleneck for the study of resistance inheritance basis. In addition, it is reported that factitious bacterial challenge test is a good way to obtain experiment materials of piglets’ bacterial diarrhea at present.This study carried out challenge test with E. coli F18ac strain in Meishan post-weaning piglets, then adopted intestinal bacteria detection, bacteria counting, small intestinal epithelial cell adhesion test to verify the test result. The aim of this study was to attain individuals of the resistance and susceptibility to E. coli F18, which could provide valuable material for analyzing the molecular mechanism of the resistance to E. coli F18, and theoretical reference for further establishing bacterial disease model in Chinese native pig breeds. Secondly, combining the previous progress of our research group in Sutai piglets, this study preliminary explored the gene expression levels of glycosphingolipid biosynthesis-ball series and the inflammatory immune pathway related genes in Meishan test group. The study designed to analyse the regulative mechanism of the resistance to E. coli F18 of Meishan, then provide some scientific basis for breeding for disease resistance of diarrhea which induced by E. coli F18 on local breeds, eventually. The main results were as follows:1. The results showed that there existed three extreme phenotypes of severe diarrhea, mild diarrhea and normality after challenge experiment in Meishan piglets. The quantity of bacterias in the intestinal contents of diarrhea piglets was more than that of normal piglets. Moreover, the adhesion test further showed that many bacterias had adhered to the epithelial cells of the small intestine of diarrhea piglets, however almost no adhesion in normal piglets’ cells. Pathological tissue section result showed that congestion phenomenon appeared in the clearance, villus of ileum tissue mucous layer fell off and the pile length of diseased intestinal mucosa became shorter, in severe diarrhea piglets. It is could speculate that E. coli F18 mainly affected the integrity of small intestinal villus when it combined with intestinal epithelial cell receptors, thus E. coli F18 settled and bred, then caused piglet diarrhea.From the above results, it was observed that the piglets diarrhea was indeed caused by E. coli F18 attack, and this study obtained several full-sib Meishan individuals of the resistance and susceptibility to E. coli F18, in other words, the diarrhea model of Meishan post-weaing piglets had been established successfully, which provided effective ways and means for obtaining basic materials on the genetic mechanisms of pigs’bacterial diarrhea and disease-resistant breeding base group.2. RT-PCR was used to detect the expression levels of Glycosphingolipid biosynthesis-globo series, inflammatory and immune pathway related genes between E. coli F18-resistant and-sensitive Meishan piglets. The results revealed that there were no significant difference between E. coli F18-resistant and -sensitive individuals about glycosphingolipid biosynthesis-globo series related genes (P>0.05). The expression levels of TNF-α and IL-1β genes in resistant group were significantly higher than that of sensitive group in spleen (P<0.05), the TNF-a expression level in resistant group was significantly higher than that of sensitive group in lymph node (P<0.05), and the SLA-3 expression level in resistant group was also significantly higher than that of sensitive group in thymus (P<0.05). Besides, The expression levels of BPI gene in resistant group were significantly higher than that of sensitive group in duodenum (P<0.01). The above results indicated that the hereditary basis and regulative mechanism of anti-51. coli F18 between native pig breeds and exotic pig breeds were indeed different. Inflammatory and immune related genes might exist important adjusting role in anti-E. coli F18 in post-weaning Meishan piglets, while the glycosphingolipid biosynthesis-globo series related genes which played an important regulation might not be involved. |
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