The Regularity About O-islands Loss In EHEC O157:H7 And Genes Loss In OI45 Effect On Stx2 Expression

Escherichiacoli O157:H7 is an important foodbome pathogen that can cause a variety of diseases,such as:hemorrhagic colitis(HC),hemolytic uremic syndrome(HUS),and thrombotic thrombocytopenic purpura(TTP).In 2001,the complete genome sequences of Enterohemorrhagic E.coli(EHEC)O157:H7 EDL933 and SAKAI were published by the American and Japanese scientists respectively.Comparing with the complete genome sequence of E.coli K12,the sequence of EDL933 insert many ectogenic gene.So we called these specific genes "O" island (OI).The concept of O-island is the extention of pathogenicity island.OI encoded many genes that have relation with virulent factor of EHEC O157:H7.Our laboratory have detected the information about the loss of O-islands in 198 strains that produce Stx by using of pathogenicity islands oligonucleotide microarray and found some strains lost some genes in O-islands.In order to study the regularity about the loss O-islands and the relation between lost genes in O-islands and bacterial virulence,I analyzed and sorted these results by using Cluster3.0 and TreeView,then the results were sorted by Algroup,A2group,B group,KM group(A1,A2 stand side by side with B,So I called it A1,A2 respectively.)The part genes in OI43 OI45 OI50 OI93 OI108 were generally lost in A1,A2,B groups;The part genes in OI50,OI76 were lost in KM.Other lost genes distribute different islands in A1,A2,B group.We respectively choiced 10 strains from A1,A2,B group and used PCR to detect above-mentioned genes,then We found only the part genes of OI45,OI50,OI93,OI108 were generally lost in these there groups and genes in other islands were not generally lost.Stx2 that is encoded by OI45 is the important virulence factor of EHECO157:H7.I carried out research about OI45 to study if the loss genes in OI45 influence the expression stx2.Frist I choiced 20 strains from A1,A2,B randomly,then amplified all genes in OI45.Finally I obtain all strains' lost information about OI45 and I sort these strains five groups according to lost regularity.On basis of these results,I extracted RNA of every group and applied RT-PCR to analyze if there is difference in expression of toxin in transcriptive lever.At the same time,I apply cytotoxic experiment to analyze if there is difference in the expression of toxin in proteinic lever.It was found that the loss of genes in OI45 can result in the difference of stx2 expression.It is suggested that the loss of genes in pathogenicity island(PAI)may influence bacterial virulence.