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Journal of Clinical Microbiology, February 2000, p. 547-551, Vol. 38, No. 2
0095-1137/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Comparison of Sorbitol MacConkey Agar and a Two-Step Method Which Utilizes Enzyme-Linked Immunosorbent Assay Toxin Testing and a Chromogenic Agar To Detect and Isolate Enterohemorrhagic Escherichia coli

Thomas J. Novicki,1,* Judy A. Daly,2 Susan L. Mottice,3 and Karen C. Carroll1

Department of Pathology, University of Utah School of Medicine and ARUP Laboratories,1 Department of Pathology, University of Utah School of Medicine and Primary Children's Medical Center,2 and Division of Laboratory Services, Utah Department of Health,3 Salt Lake City, Utah 84113

Received 29 March 1999/Returned for modification 7 June 1999/Accepted 28 September 1999

Enterohemorrhagic Escherichia coli (EHEC) and specifically serotype O157:H7 are a significant cause of hemorrhagic gastrointestinal disease and the hemolytic uremic syndrome. Methods currently used in clinical microbiology labs, such as sorbitol-MacConkey (SMAC) agar, reliably detect only O157:H7. We have evaluated a two-step method that has the potential to identify and isolate all EHEC serotypes, including serotype O157:H7. This method utilizes a chromogenic selective-differential medium for the isolation of E. coli together with an enzyme-linked immunosorbent assay (ELISA) that detects the Shiga-like toxins Stx1 and Stx2. Both are commercially available and usable in a wide range of clinical microbiology laboratories. Compared to a Vero cell cytotoxic assay, SMAC had sensitivities of 23.5% for the identification of all EHEC serotypes and of 50.0% for the identification of O157:H7 alone. The two-step method had sensitivities of 76.5 and 100%, respectively. The ELISA alone had a sensitivity of 82.4% in the detection of Stx1 and Stx2. The specificity was 100% in all cases. Overall, 14 EHEC isolates were obtained: 8 (58%) O157:H7, 2 (14%) O26, 2 (14%) O111:NM, 1 (7%) O103:H2, and 1 (7%) O121:H19. All but one were isolated during the months of May to September. The two-step method was found to be considerably more expensive than SMAC for both positive and negative samples.


* Corresponding author. Mailing address: Fred Hutchinson Cancer Research Center, 1100 Fairview Ave. N, AB-110, P.O. Box 19024, Seattle, WA 98109-1024. Phone: (206) 667-2448. Fax: (206) 667-6250. E-mail: tnovicki{at}fhcrc.org.


Journal of Clinical Microbiology, February 2000, p. 547-551, Vol. 38, No. 2
0095-1137/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.



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