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Applied and Environmental Microbiology, October 2007, p. 6360-6369, Vol. 73, No. 20
0099-2240/07/$08.00+0     doi:10.1128/AEM.00316-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Molecular Subtyping and Genetic Analysis of the Enterohemolysin Gene (ehxA) from Shiga Toxin-Producing Escherichia coli and Atypical Enteropathogenic E. coli{triangledown}

Adrian L. Cookson,1* Jenny Bennett,2 Fiona Thomson-Carter,2 and Graeme T. Attwood1

Food, Metabolism and Microbiology Section, Food and Health Group, AgResearch, Grasslands Research Centre, Tennent Drive, Palmerston North,1 Enteric Reference Laboratory, ESR Kenepuru Science Centre, Porirua, New Zealand2

Received 8 February 2007/ Accepted 9 August 2007

Analyses of the distribution of virulence factors among different Escherichia coli pathotypes, including Shiga toxin-producing E. coli (STEC), may provide some insight into the mechanisms by which different E. coli strains cause disease and the evolution of distinct E. coli types. The aim of this study was to examine the DNA sequence of the gene for enterohemolysin, a plasmid-encoded toxin that readily causes the hemolysis of washed sheep erythrocytes, and to assess the distribution of enterohemolysin subtypes among E. coli isolates from various human and animal sources. The 2,997-bp ehxA gene was amplified from 227 (63.8%) of 356 stx- and/or eae-positive E. coli strains isolated from cattle and sheep and from 24 (96.0%) of 25 STEC strains isolated from humans with diarrheal disease. By using PCR and restriction fragment length polymorphism (RFLP) analysis of ehxA, six distinct PCR-RFLP types (A to F) were observed, with strains of subtypes A and C constituting 91.6% of all the ehxA-positive strains. Subtype A was associated mainly with ovine strains with stx only (P < 0.001), and subtype C was associated with bovine eae-positive strains (P < 0.001). Eleven ehxA alleles were fully sequenced, and the phylogenetic analysis indicated the presence of three closely related (>95.0%) ehxA sequence groups, one including eae-positive strains (subtypes B, C, E, and F) and the other two including mainly eae-negative STEC strains (subtypes A and D). In addition to being widespread among STEC strains, stx-negative, eae-positive strains (atypical enteropathogenic E. coli strains) isolated from cattle and sheep have similar ehxA subtypes and hemolytic activities.

* Corresponding author. Mailing address: Food, Metabolism and Microbiology Section, Food and Health Group, AgResearch, Grasslands Research Centre, Tennent Drive, Private Bag 11008, Palmerston North 4442, New Zealand. Phone: 64 6 351 8229. Fax: 64 6 351 8003. E-mail: adrian.cookson{at}agresearch.co.nz

{triangledown} Published ahead of print on 24 August 2007.

Applied and Environmental Microbiology, October 2007, p. 6360-6369, Vol. 73, No. 20
0099-2240/07/$08.00+0     doi:10.1128/AEM.00316-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Cookson, A. L., Bennett, J., Nicol, C., Thomson-Carter, F., Attwood, G. T. (2009). Molecular Subtyping and Distribution of the Serine Protease from Shiga Toxin-Producing Escherichia coli among Atypical Enteropathogenic E. coli Strains. Appl. Environ. Microbiol. 75: 2246-2249 [Abstract] [Full Text]  


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