The Epidemiological Investigation Of STEC From One Cattle Farm In Jiangsu Province And Their Genetic Relatedness Analysis

Shiga toxin-producing Escherichia coli (STEC), also called Vero toxin-producing E.coli (VTEC), is a zoonotic agent which causes a potentially fatal human illness, and EHEC O157:H7 is one of the typical representatives. These pathogens could infect the elderly and children of the weaker resistance and show those clinical symptoms:diarrhoea, haemorrhagic colitis (HC), and the haemolytic uraemic syndrome (HUS). The isolation, identification and the pathogenicity research of STEC was carried out in a cattle farm in Jiangsu Province. Besides, we slso do the Pulsed field gel electrophoresis (PFGE) to analyze the genetic relatedness. These investigation play an important role in epidemiological survey.1 Isolation and characterization of STEC strains from a cattle farm in Jiangsu ProvinceThrough investigating the cattle farm in Jiangsu Province for STEC in March, June, September, December of 2014, we isolate STEC from those samples to determine the prevalence of STEC in the dairy farm. Genes of stxl, stx2, EaeA, EhxA were detected with multiple PCR technique, which had been set up in this laboratory, and the positive samples were picked out by this method and colony features on cefixime potassium tellurite sorbitol-MacConkey agar (CT-SMAC). Genes of stx1, stx2, EaeA, EhxA of positive samplesare detected by primary screening using multiple PCR, then continue to purity the positive sample for pure cultures. In this cattle farm of Jiangsu Province, the total screening rate is 16.29%, the total isolation rate is 3.75%, the screening rate of calves is 28.75%, the isolation rate of calves is 7.5%.In this study,12 different O serotypes were determined, and these serotypes include STEC 055, which had caused severely and potentially fatal disease, and 055 is one of the predominated serotypes in this farm.The female BALB/c mice of 3 weeks were choosen as the animal model of STEC in this research. Four strains were inoculated to Vero cells. It is observed that cells became round, shrinkage and die gradually. The number of died mice varied with different inoculated isolates. Colon muscosal epithelial necrosis was observed in challenged mice and infiltration of neutrophils was observed in the liver and spleen. The mortality of the mice in challenged group, microscopic examination and cytotoxicity text on Vero cells revealed the isolated STEC strains isolated in this study are pathogenic.2 The genetic relatedness analysis of STEC strains isolated from a dairy farm in Jiangsu ProvinceA genemic profile map of 13 different STEC strains was obtained by pulsed field gel electrophoresis, then phylogentic tree was constructed using unweighted pairgroup mean arithmetic (UPGMA) to make cluster analysis and analyze the genetic correlation.17 different enzymatic maps were obtained by enzyme digestion, their similarity index varied from 41.8% to 90.3%. The similarity indexof four strains has reached 80%, and theothers was less than 80%. These results reflected that the affinity of the STEC strains isolated from the calves was low, and STEC clones were rich. The STEC strains originated from this farm were very diverse. It implied that these strains exert a threat to both food safety and public health.