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J. Clin. Microbiol. doi:10.1128/JCM.00596-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Comparison between O serotyping method and multiplex real-time PCR to identify diarrheagenic Escherichia coli in Taiwan

Research and Diagnostic Center, Centers for Disease Control, Department of Health, Taipei, Taiwan, Center of General Education, National Taipei College of Nursing, Taipei, Taiwan, School of Medical Laboratory Science and Biotechnology, Taipei Medical University, Taipei, Taiwan

^* To whom correspondence should be addressed. Email: wuhs{at}cdc.gov.tw.

	Abstract

To compare the diarrheagenic E. coli (DEC) identification between traditional O-serotyping and modern virulence gene detection assays, we developed a multiplex real-time PCR assay by detecting six specific virulence genes for EPEC, EHEC, ETEC, and EIEC. Among 261 clinical diarrheal stool samples, a total of 137 suspected diarrheagenic E. coli (sDEC) isolates were identified by commercially available antisera. The most prevalent serogroups were O1 (12/137, 8.7%), O25 (9/137, 6.5%), and O44 (9/137, 6.5%). The specific virulence genes of the 137 sDEC were analyzed by the multiplex real-time PCR assay. Fifteen (10.9%) out of 137 were confirmed as true DEC (tDEC), indicating that serotypic markers did not correlate with specific virulence genes. Enterotoxigenic E. coli (ETEC, 66.7%) was the most prevalent, followed by enteroinvasive E. coli (EIEC, 20%) and enteropathogenic E. coli (EPEC, 13.3%). No enterohemorrhagic E. coli (EHEC) was identified from the specimens. Four novel serotypes were found in the study, 2 in EPEC (O111:H9, O63:H6) and 2 in EIEC (O63:H9 and O169:H9). In conclusion, the real-time PCR assay considerably reduces the high false positive rate of using serotyping alone, and thus it is suggested that serogrouping-based methods are inadequate for identifying DEC, albeit useful for a limited number of serogroups. In addition, ETEC, EPEC and EIEC was present in 5.7% (15/261) of the diarrheal patients in northern Taiwan in 2006.