Virulence determinants in shiga toxin (stx) negative esherichia coli O157 strains isolated from hangzhou, China

摘要

Since Kauffmann developed Esherichia coli serotyping system about half century ago, serotypes have been used as marker of diarrheagenic E. coli in diagnosis and epidemiological investigation. However, pathogenicity of bacteria depends on virulence factors that htey present. Virulence determinants become one of important bases for categorizing diarrheagenic E. coli. According to Schmidt(1), E. colie serogroup O157 can be broken down into three pathogroups based on the virulence determinants expressed by them. (1) Enterohemorrhagic E. coli (EHEC) O157:H7 and H~- strains, which produce Shiga toxin (Stx), harbor a 60 megadalton large plasmid which have hemolysin gene (hly), and possess locus of enterocyte effacement (LEE) in chromosome, in which eaeA encode intimin important for attaching-and-effacing lesions. EHEC O157 strains may cause hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS), resulting in very serious outbreaks of these diseases in the United States, the United Kingdom ,Germany, Japan, etc. (2) Enterotoxigenic E.coli (ETEC) strains of various H-antigen types express K88 fimbriae and enterotoxins. They are associated mainly with colibacillosis in pigs. (3) Enteropathogenic E. coli (EPEC) strains, presenting EPEC eae gene and EPEC adherence factor (EAF), are associated with infantile diarrhea.