Article Title

Characterization of Escherichia coli Serotype O157 Strains Isolated in Taiwan by PCR and Multilocus Enzyme Analysis


Escherichia coli serotype O157 strains were isolated from fecal samples of cattle and sheep, as well as raw meat in Taiwan from July 1997 to June 1999. In total, six strains of E. coli serotype O157 were collected. Of these, only one strain, isolated from fecal samples of sheep, was characterized as E. coli O157:H7. The remaining five strains were determined as H41, H45, H? (non-typeable with 43 O-antisera) and NM (non-motile). All six strains were analyzed for pathogenic genes of Enterohemorrhagic E. coli (EHEC) by the Polymerase chain reaction (PCR) method. The E. coli O157:H7 was the only strain harbored the virulent genes of slt2, eaeA and hlyA. Meanwhile, this strain was unable to ferment sorbitol and lacked β-D-glucuronidase activity. The five non-H7 serotype of E. coli O157 strains were further subjected to PCR analysis for other pathogenic genes, including genes in Enterotoxigenic E. coli (ETEC, heat-labile enterotoxin, LT, heat-stable enterotoxin, ST), Enteroinvasive E. coli (EIEC, invasive plasmid) and Enteropathogenic E. coli (EPEC, adherence factor, EAF). Results revealed that the five non-H7 strains did not carry any of the above mentioned genes. To better understand the genetic relatedness among six isolated strains, ten enzyme loci were delineated using the multilocus enzyme analysis. Six strains were designated to five electrophoretic types. Cluster analysis further revealed that the five non-EHEC O157 and one EHEC E. coli O157:H7 strains belong to two distinct clones, respectively. These results suggested that non-EHEC O157 and EHEC E. coli O157:H7 strains isolated in the Taiwan area most likely originated from two clones. Furthermore, the genetic relatedness among indigenous E. coli O157 strains in Taiwan was elucidated through this multilocus enzyme analysis.

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