Isolation And Characterization Of Escherichia Coli O157 From Beef,Pork And Cattle Feces And Finding Of Genes Associated With Adherence To HEp-2 Cells

In the periods from September to November 1996, beef and pork samples were collected at weveral free amrkets of Changchun, and fecal samples from adult cattle were collected at two farms and two slaughterhouses ofChangchun between May and August 1997. The samples were examined for presence of Shiga toxin producing Escherichia coli of serogroup O157.Escherichia coli O157 strains wre isolated from 2(5%) of 40 beef, 1(3.3%) of 30 pork, and 3(1.7%) of 176 adult cattle fecal samples. All strains werepositive for both stx (stx1 and/or stx2) and Escherichia coli attaching-and-effacing(eae) gene sequences, and was able to produce Stx,All strains werefound to adhere to HEp-2 cell with a localized adherence(LA) pattern. Therefore, they were regarded as human pathogens. Phage types 4,8 and 47 were observed in the above Escherichia coli O157:H7strains. Two beefstrains and a strain previously isolated from human in Shandong, China, shared phage type 4 and had a similar Pulsed Field Gel Electrophoresis (PFGE) patters, suggesting the possibility of Fool-borne transmission. Cattleseem to be a reservoir of Escherichia coli O 157:H7 and meat products weresubjected to contamination of this pathogen on Changchun area. Consumption of contaminated meat might, therefore, be a source of human infection ofEscherichia coli O157:H7 in Changchun ,China. Escherichia coli O157:H7 strains have been shown to adhere to HEp-2 cells. We constructed 5 TnphoA insertion mutants of Escherichia coli O157: H7 strain 97094 that are79unable to adhere to HEp-2 cells. Each TnphoA insert along with flankingEscherichia coli O157:H7 sequences was cloned.The cloned DNA portionof Escherichia coliO157:H7 was sequenced using the oligonucleotideprimer that hybridizes to pho A sequences just down stream of the fusion joint.The sequences were searched for their homology using BLAST.TnphoA wasfound to have inserted to eae in four mutants, to ycbR gene in one mutant andbetween the start point and the-10 sequence of Z4182 gene in another mutant.YCBR are a putative fimbrial chaperone required for the biogenesis of the putative YCBQ fimbia, and the function of Z4182 gene is unknown. Thesedata suggest that YCBR and the product of Z4182 gene are associated with adherence ofEscherichia coli to epithelial cells in vitro.