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Infection and Immunity, December 2002, p. 6853-6859, Vol. 70, No. 12
0019-9567/02/$04.00+0     DOI: 10.1128/IAI.70.12.6853-6859.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Molecular Characterization of a Serotype O121:H19 Clone, a Distinct Shiga Toxin-Producing Clone of Pathogenic Escherichia coli

Cheryl L. Tarr,1 Teresa M. Large,1 Chris L. Moeller,1 David W. Lacher,1 Phillip I. Tarr,2 David W. Acheson,3 and Thomas S. Whittam1*

Microbial Evolution Laboratory, National Food Safety and Toxicology Center, Michigan State University, East Lansing, Michigan 48824,1 Children's Hospital and Regional Medical Center, University of Washington School of Medicine, Seattle, Washington 98105,2 University of Maryland School of Medicine, Baltimore, Maryland 212013

Received 14 June 2002/ Returned for modification 7 August 2002/ Accepted 5 September 2002

Most illnesses caused by Shiga toxin-producing Escherichia coli (STEC) have been attributed to E. coli serotype O157:H7, but non-O157 STEC infections are now increasingly recognized as public health problems worldwide. The O121:H19 serotype is being isolated more frequently from clinical specimens and has been implicated in one waterborne outbreak. We used multilocus virulence gene profiling, a PCR-based assay, to characterize the virulence gene content of 24 isolates of serotype O121:H19 and nonmotile variants. We also performed multilocus enzyme electrophoresis and multilocus sequencing to establish the clonal relatedness of O121 isolates and to elucidate the relationship of O121 to common STEC clones. The 24 isolates were found to represent a single bacterial clone, as there was no allelic variation across 18 enzyme loci among the isolates. The complete nucleotide sequence of the intimin gene differed by four substitutions from that of the epsilon (Int-{varepsilon}) allele of O103:H2 strain PMK5. The typical O121 virulence gene profile was similar to the profiles of enterohemorrhagic E. coli (EHEC) clones of E. coli: it included a Shiga toxin 2 gene (stx2), two genes on the EHEC plasmid (toxB and ehxA), and the gene encoding intimin (eae). Despite the similarities, putative virulence genes distributed on O islands—large chromosomal DNA segments present in the O157:H7 genome—were useful for discriminating among STEC serotypes and the O121:H19 clone had a composite profile that was distinct from the profiles of the other major EHEC clones of pathogenic E. coli. On the basis of sequencing analysis with 13 housekeeping genes, the O121:H19 clone did not fall into any of the four classical EHEC and enteropathogenic E. coli groups but instead was closely related to two eae-negative STEC strains.

* Corresponding author. Mailing address: Microbial Evolution Laboratory, 165 Food Safety and Toxicology Building, Michigan State University, East Lansing, MI 48824. Phone: (517) 432-3588. Fax: (517) 432-2310. E-mail: whittam{at}msu.edu.

Editor: J. T. Barbieri

Infection and Immunity, December 2002, p. 6853-6859, Vol. 70, No. 12
0019-9567/02/$04.00+0     DOI: 10.1128/IAI.70.12.6853-6859.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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