| Shiga toxin-producing Escherichia coli (STEC) is a zoonotic agent which can cause food-borne infections and severe even potentially fatal illness in humans. STEC can cause diarrhea and hemorrhagic colitis (HC) and may lead to heamolytic ureamic syndrome (HUS).STEC has been identified as a significant health problem because of its association with large outbreaks and with HUS, which can lead to kidney faiture and death in some individuals. The STEC serotype distribution in different areas may be not identical.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 attributed to serotype O157:H7, but now non-0157STEC are more prevalent than0157:H7. Ruminants, especially cattle, are the main reservoirs of STEC. The most frequent non-0157which are associated with human infections are O26:H11, O103:H2,0111:H8, O145:H28.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 amongs2dairy cattle herds and2beef cattle herds in Jiangsu Province for STEC from January,2013to January,2014. It is expected to clarify the differences of the prevalence of STEC in different periods in local cattle herds and further to control the prevalence of human diseases associated with STEC better.Polymerase chain reaction (PCR) to detect genes of eaeA, stx1, stx2, ehxA was carried out, which had been developed in this laboratory previously.O157STEC 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 in19of641the beef cattle faecal samples (3.0%), while dairy cattle faecal samples reached a higher percentage (7.3%,63/864). 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. There are many differences between the stx positive rates and isolation rates of the same herds in the same month of different years. And the distribution of genes in the same herds of the same month in different years has a large difference, too. stx screening rate of January,2013and January,2014in the same herd is7.1%and3.9%, respectively. Both them are lower than May,2013(12.5%).33STEC strains were recoverd from faecal samples (33/1505,2.2%). These STEC isolates belonged to13O serotypes and13O:H serotypes. Serotype02,05,015,055,065,068, O109had been reported to be associated with human diseases. STEC065strains were recovered in several farms and in the different months.In this study, BALB/c mouse model of STEC infection was developed,065serotype was lethal to mouse in this model.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 from6STEC (065) isolated from different farms revealed that these6strains had6different PFGE patterns, and belonged to four different clusters. This result implied that the PFGE of STEC stains were closely related to the virulence-associated genotypes. Although these bovine originated isolates do not cause any clinical symptoms in cattle, they exert a threat to food safety and public health.The stains which carry eaeA, stxl,ehxA genes were belonged to ST342. And the stains carrying stx2gene were belonged to ST329. The results of the multilocus sequence typing (MLST) of6stains showed that the same virulence-associated genotype and serogroup from different farms stains have the same ST, suggesting that they might came from a same ancestor. |
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