Epidemiologic study of results of pulsed-field gel electrophoresis of isolates of Rhodococcus equi obtained from horses and horse farms

Noah D. CohenDepartment of Large Animal Medicine and Surgery, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843-4475.

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Karen E. SmithDepartment of Large Animal Medicine and Surgery, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843-4475.

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Thomas A. FichtDepartment of Veterinary Pathobiology, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843-4475.

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Shinji TakaiDepartment of Animal Hygiene, School of Veterinary Medicine and Animal Sciences, Kitasato University, Towada, Aomori 034, Japan.

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Melissa C. LibalTexas Veterinary Medical Diagnostic Laboratory, College Station, TX 77841-3040.

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Brian R. WestApplied Maths, 512 E 11th St, Ste 207, Austin, TX 78701.

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Lemuel S. delRosarioApplied Maths, 512 E 11th St, Ste 207, Austin, TX 78701.

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Teotimu BecuClinica Equina, Alem y 29 de Juno, Capitan Sarmiento, Buenos Aires CP 2752, Argentina.

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Desmond P. LeadonIrish Equine Centre, Naas, County Kildare, Ireland.

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Thomas BuckleyIrish Equine Centre, Naas, County Kildare, Ireland.

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M. Keith ChaffinDepartment of Large Animal Medicine and Surgery, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843-4475.

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Ronald J. MartensDepartment of Large Animal Medicine and Surgery, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843-4475.

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Abstract

Objective—To compare isolates of Rhodococcus equi on the basis of geographic source and virulence status by use of pulsed-field gel electrophoresis (PFGE).

Sample Population—290 isolates of R equi(218 virulent isolates from foals and 72 avirulent isolates from feces, soil, and respiratory tract samples) obtained between 1985 and 2000 from horses and horse farms from 4 countries.

Procedure—DNA from isolates was digested with the restriction enzyme AseI and tested by use of PFGE. Products were analyzed for similarities in banding patterns by use of dendrograms. A similarity matrix was constructed for isolates, and the matrix was tested for nonrandom distributions of similarity values with respect to groupings of interest.

Results—There was little grouping of isolates on the basis of country, virulence status, or region within Texas. Isolates of R equi were generally < 80% similar, as determined by use of PFGE. Isolates from the same farm generally were rarely of the same strain.

Conclusions and Clinical Relevance—Considerable chromosomal variability exists among isolates of R equi obtained from the same farm, sites within Texas, or among countries from various continents. Only rarely will it be possible to link infections to a given site or region on the basis of analysis of isolates by use of PFGE of chromosomal DNA. (Am J Vet Res 2003;64:153–161)

Abstract

Objective—To compare isolates of Rhodococcus equi on the basis of geographic source and virulence status by use of pulsed-field gel electrophoresis (PFGE).

Sample Population—290 isolates of R equi(218 virulent isolates from foals and 72 avirulent isolates from feces, soil, and respiratory tract samples) obtained between 1985 and 2000 from horses and horse farms from 4 countries.

Procedure—DNA from isolates was digested with the restriction enzyme AseI and tested by use of PFGE. Products were analyzed for similarities in banding patterns by use of dendrograms. A similarity matrix was constructed for isolates, and the matrix was tested for nonrandom distributions of similarity values with respect to groupings of interest.

Results—There was little grouping of isolates on the basis of country, virulence status, or region within Texas. Isolates of R equi were generally < 80% similar, as determined by use of PFGE. Isolates from the same farm generally were rarely of the same strain.

Conclusions and Clinical Relevance—Considerable chromosomal variability exists among isolates of R equi obtained from the same farm, sites within Texas, or among countries from various continents. Only rarely will it be possible to link infections to a given site or region on the basis of analysis of isolates by use of PFGE of chromosomal DNA. (Am J Vet Res 2003;64:153–161)