Isolation And Characterization Of STEC Strains Originated From Several Cattle Farms In Jiangsu Province And Their Genetic Relatedness Analysis

Shiga toxin-producing Escherichia coli (STEC) is a zoonotic agent which causes a potentially fatal human illness which clinical spectrums include diarrhoea, haemorrhagic colitis, and the haemolytic uraemic syndrome (HUS). STEC is of serious public health concern because of its association with large outbreaks and with HUS, which is the leading cause of acute renal failure in children. Many STEC serotypes have been associated with human illness, the vast majority of reported outbreaks and sporadic cases of STEC-infection in humans have been associated with serotype O157:H7, but non-0157:H7infections are more and more frequent too.Ruminants, especially cattle, are the main reservoirs of STEC. Infection is typically acquired through the ingestion of contaminated food or water, through direct contact with animals, or via person to-person transmission.1. Isolation and characterization of STEC strains originated from several farms in Jiangsu ProvinceThrough investigating among4beef cattle herds and2dairy cattle herds in Jiangsu Province for STEC during April to November in2011, polymerase chain reaction (PCR) to detect genes of eaeA, stxl, stx2, ehxA was carried out, which had been developed in this laboratory previously.0157STEC and non-0157STEC isolates were picked out using multiple PCR and colony colour (white or red) on cefixime potassium tellurite sorbitol-MacConkey agar (CT-SMAC). stx genes were detected in25of the256beef cattle faecal samples (9.8%), while dairy cattle faecal samples reached a higher percentage (20.2%,214/1059). Furthermore, different cattle herds exhibited various stx positive rates and isolation rates in the same month, and the stx positive rates and isolation rates also varied with the season.51STEC strains were recoverd from faecal samples (51/1315,3.9%). These STEC isolates belonged to13O serotypes and16O:H serotypes. Serotypes O26,O49,O55,O65,O68,074,0109,0136,0153,0157had been reported to be associated with human diseases, and serotypes O26:H11and O157:H7were involved in HUS.0109and074were the predominant serotypes, and STEC074strains were recovered in several farms.In this study, BALB/c mouse model of STEC infection was developed,0serotypes were observed to be associated with the mouse lethality, O157:H7serotype strains experienced a higher lethality than the other serotype strains (0109and026).2Genetic relatedness analysis of STEC strains originated from several cattle farmsPulsed field gel electrophoresis (PFGE) was used to analyze the phylogenetic relationship among STEC strains isolated from different cattle species and farms.PFGE of XbaI-digested chromosomal DNA from30STEC (O109) isolated from one dairy farm (dairy cattle farm A) revealed that these30isolates had a same PFGE pattern, and suggested that they were the same phylogenetic cluster. These results strongly suggested that0109STEC is the predominant serogroups in this farm.Low Dice coefficients (49%-73%) were obtained from13different serotype STEC strains based on PFGE patterns. This result implied that various STEC pools contributed to the potential threats to human health by these food-born pathogens. Although these bovine originated isolates do not cause any clinical symptoms in cattle, they exert a threat to food safety and public health.