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Journal of Clinical Microbiology, February 2005, p. 546-550, Vol. 43, No. 2
0095-1137/05/$08.00+0     doi:10.1128/JCM.43.2.546-550.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Distribution of the Urease Gene Cluster among and Urease Activities of Enterohemorrhagic Escherichia coli O157 Isolates from Humans

Alexander W. Friedrich,* Robin Köck, Martina Bielaszewska, Wenlan Zhang, Helge Karch, and Werner Mathys

Institut für Hygiene, Universitätsklinikum Münster, Münster, Germany

Received 23 August 2004/ Returned for modification 29 September 2004/ Accepted 17 October 2004

Enterohemorrhagic Escherichia coli (EHEC) O157 strains belong to two closely related major groups, which are differentiated by their sorbitol fermentation phenotypes. Here we studied the conservation of urease genes and their expression in sorbitol-fermenting (SF) and non-SF EHEC O157 isolates. PCR targeting ure genes (ureA, -B, -C, -D, -E, -F, and -G) demonstrated that each of these genes was present in 58 of 59 EHEC O157:H7 isolates. In contrast, none of 82 SF EHEC O157:NM (nonmotile) isolates contained any of the ure genes. Hence, the absence of the urease genes distinguishes SF EHEC O157:NM strains from EHEC O157:H7, but this absence demonstrates that the urease genes are not useful genetic targets for the detection of EHEC strains, because SF EHEC O157:NM strains are missed by such a strategy. When examined for urease activity on Christensen agar and in the API 20E system, only one O157:H7 strain displayed urease activity and produced elevated levels of ammonia, which was subsequently confirmed by ammonia electrode measurement. Because the ure genes were absent from each of nine strains of E. coli O55:H7, the proposed progenitor of EHEC O157, we hypothesize that EHEC O157:H7 diverged from the evolutionary pathway at an early stage and then acquired the O islands carrying the ure gene cluster.

* Corresponding author. Mailing address: Institut für Hygiene, Universitätsklinikum Münster, Robert-Koch Str. 41, 48149 Münster, Germany. Phone: 49-251-8355366. Fax: 49-251-8355341. E-mail: alexf{at}uni-muenster.de.

Journal of Clinical Microbiology, February 2005, p. 546-550, Vol. 43, No. 2
0095-1137/05/$08.00+0     doi:10.1128/JCM.43.2.546-550.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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