| Diarrhea is one of the most serious piglets disease which often leads to decline of piglet survival rate, growth slowing down or stagnation, or even death. It has become a big problem in China's pig breed industry and has caused tremendous economic losses to China's animal husbandry industry. Piglet diarrhea caused by many reasons, but the pathogenic Escherichia coli is recognized as the main pathogen which cause diarrhea in newborn animal and weaning newborn animal. The way of vaccination often failed by the unceasing changing of Escherichia coli serotypes that increased the difficulties of disease prevention and control of Escherichia coli to pigs. People use antimicrobial agents as feed additives to control diarrhea and use antimicrobial agents extensively and irrationally in veterinary clinical treatment often leading to Escherichia coli resistant strains appearance, resistance spectrum expanded, especially the phenomenon of multiple drug resistance become more seriously. Escherichia coli as one of the plasmid-mediated resistance of bacteria, it's resistance can be transmission horizontally by plasmid, and thus brought difficulty to treat diseases which causing by Escherichia coli. Therefore, it can provide a reference for clinical medicine, and lay the foundation for the understanding of its epidemiology of serotypes investigation, drug resistance detection and plasmid graph analysis.In this study, bacteria were isolated from fecal samples of diarrhea piglets collected from farms of Northern and Guanzhong and Southern of Shaanxi province. And 20 kinds of standard single-factor O serotypes were used for serotypes investigation. The antimicrobial susceptibilities of 11 kinds to 26 antibiotics of 104 enteropathogenic Escherichia coli were determined by using Kirby-Bauer method based on the performance standards for anti-microbial susceptibility testing recommended by CLSI, and 11 drug-resistant strains were analyzed for molecular typing and plasmid homology cluster. We obtained the following results:1. 121 strains of Escherichia coli were isolated and identified by separation culture, biochemical identification and hemolytic test from 142 piglet fecal samples collected from 7 farms of different regions of Shaanxi province. With standard serum of anti-Escherichia coli, 104 strains were typed and those strains covering 13 serotypes. O80, O139 and O141 were the advantages of serotypes of Escherichia coli in Shaanxi province.2. Four antibioties showed 0 resistance rate, including piperacillin, ceftazidime, polymyxin B and furazolidone. Four antibioties of resistance rate were under 15% , including cefazolin (15%), cefradine (12%), cefoperazone (12%) and cefuroxime(8%). Amikaci (23%), neomycin (27%) and ofloxacin (27%) were under 30%. Seven antibioties of resistance rate were above on 85%, including benzylpenicillin, doxycycline, tetracycline, carbenicillin, compound sulfamethoxazole, chloramphenicol and ampicillin. 100% Resistance rate had two antibioties, including Oxacillin and Clindamycin. Multi-drug resistance testing showed that 71% Escherichia coli strains were between 8 and 13 of antibioties resistance, 1~7 resistant strains accounted for 17%, 12% strains above on 13 resistant, and showed increasing trend from south to north of Shaanxi region.3. 11 Escherichia coli strains were analysis and showed that resistance type and plasmid profiles would be same or similar if isolated from same source and same time. If isolated from different source, there would be same, also be different, of resistance type of Escherichia coli strains, but plasmid profiles would be different generally. Homology clustering analysis showed that there had regional differences of epidemic of plasmid among all regions of Shaanxi Province. But this difference is not large and the differences remain within 35%. There has great homology of plasmid if isolated from same place at the same time. But if isolated from same place but not same time, the homology of plasmid will decline.
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