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Effects of iron modulation on growth and viability of Rhodococcus equi and expression of virulence-associated protein A

Misty C. JordanDepartment of Large Animal Medicine and Surgery, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843.

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Jessica R. HarringtonDepartment of Large Animal Medicine and Surgery, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843.

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

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Renee M. TsolisDepartment of Medical Microbiology, College of Medicine, Texas A&M University, College Station, TX 77843.

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Lawrence J. DangottDepartment of Biochemistry and Biophysics, College of Agriculture and Life Sciences, Texas A&M University, College Station, TX 77843.

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Eugene D. WeinbergDepartment of Biology, College of Arts and Sciences, Indiana University, Bloomington, IN 47405.

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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.

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Abstract

Objective—To determine the importance of iron for in vitro growth of Rhodococcus equi, define potential iron sources in the environment and mechanisms by which R equi may obtain iron from the environment, and assess expression and immunogenicity of iron-regulated proteins.

Sample Population—10 virulent and 11 avirulent strains of R equi.

Procedure—In vitro growth rates and protein patterns of R equi propagated in media with normal, excess, or limited amounts of available iron were compared. Immunoblot analyses that used serum from foals naturally infected with R equi and monoclonal antibody against virulence-associated protein (Vap)A were conducted to determine immunogenicity and identity of expressed proteins.

Results—Excess iron did not alter growth of any R equi strains, whereas growth of all strains was significantly decreased in response to limited amounts of available iron. Virulent R equi were able to use iron from ferrated deferoxamine, bovine transferrin, and bovine lactoferrin. Only virulent R equi expressed an iron-regulated, immunogenic, surface-associated protein identified as VapA.

Conclusions and Clinical Relevance—Iron is required for the growth and survival of R equi. Sources of iron for R equi, and mechanisms by which R equi acquire iron in vivo, may represent important virulence factors and novel targets for the development of therapeutic and immunoprophylactic strategies to control R equi infection in foals. Expression of VapA is substantially upregulated when there is a limited amount of available iron. (Am J Vet Res 2003;64:1337–1346)

Abstract

Objective—To determine the importance of iron for in vitro growth of Rhodococcus equi, define potential iron sources in the environment and mechanisms by which R equi may obtain iron from the environment, and assess expression and immunogenicity of iron-regulated proteins.

Sample Population—10 virulent and 11 avirulent strains of R equi.

Procedure—In vitro growth rates and protein patterns of R equi propagated in media with normal, excess, or limited amounts of available iron were compared. Immunoblot analyses that used serum from foals naturally infected with R equi and monoclonal antibody against virulence-associated protein (Vap)A were conducted to determine immunogenicity and identity of expressed proteins.

Results—Excess iron did not alter growth of any R equi strains, whereas growth of all strains was significantly decreased in response to limited amounts of available iron. Virulent R equi were able to use iron from ferrated deferoxamine, bovine transferrin, and bovine lactoferrin. Only virulent R equi expressed an iron-regulated, immunogenic, surface-associated protein identified as VapA.

Conclusions and Clinical Relevance—Iron is required for the growth and survival of R equi. Sources of iron for R equi, and mechanisms by which R equi acquire iron in vivo, may represent important virulence factors and novel targets for the development of therapeutic and immunoprophylactic strategies to control R equi infection in foals. Expression of VapA is substantially upregulated when there is a limited amount of available iron. (Am J Vet Res 2003;64:1337–1346)