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Applied and Environmental Microbiology, October 2004, p. 5947-5954, Vol. 70, No. 10
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.10.5947-5954.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

High-Level Genotypic Variation and Antibiotic Sensitivity among Escherichia coli O157 Strains Isolated from Two Scottish Beef Cattle Farms

Leila Vali,¹ Karen A. Wisely,¹ Michael C. Pearce,^2,3 Esther J. Turner,¹ Hazel I. Knight,^2,3 Alastair W. Smith,^2,3 and Sebastian G. B. Amyes^1*

Medical Microbiology, University of Edinburgh Medical School, Edinburgh,¹ Centre for Tropical Veterinary Medicine, University of Edinburgh, Roslin, Midlothian,² Scottish Agricultural College, Drummondhill, Inverness, United Kingdom³

Received 2 December 2003/ Accepted 31 May 2004

Escherichia coli O157:H7 is a human pathogen that is carried and transmitted by cattle. Scotland is known to have one of the highest rates of E. coli O157 human infections in the world. Two hundred ninety-three isolates were obtained from naturally infected cattle and the environment on two farms in the Scottish Highlands. The isolates were typed by pulsed-field gel electrophoresis (PFGE) with XbaI restriction endonuclease enzyme, and 19 different variations in patterns were found. There was considerable genomic diversity within the E. coli O157 population on the two farms. The PFGE pattern of one of the observed subtypes matched exactly with that of a strain obtained from a Scottish patient with hemolytic-uremic syndrome. To examine the stability of an individual E. coli O157 strain, continuous subculturing of a strain was performed 110 times. No variation from the original PFGE pattern was observed. We found three indistinguishable subtypes of E. coli O157 on both study farms, suggesting common sources of infection. We also examined the antibiotic resistance of the isolated strains. Phenotypic studies demonstrated resistance of the strains to sulfamethoxazole (100%), chloramphenicol (3.07%), and at a lower rate, other antibiotics, indicating the preservation of antibiotic sensitivity in a rapidly changing population of E. coli O157.

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* Corresponding author. Mailing address: Medical Microbiology, University of Edinburgh, Medical School, Teviot Place, Edinburgh EH8 9AG, United Kingdom. Phone and fax: 44 131 6511385. E-mail: s.g.b.amyes{at}ed.ac.uk.

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Applied and Environmental Microbiology, October 2004, p. 5947-5954, Vol. 70, No. 10
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.10.5947-5954.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

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