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


METHODS
10 virulent and 11 avirulent strains of R equi.


METHODS
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
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.
Jordan
Misty C
MC
Department of Large Animal Medicine and Surgery, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843, USA.
Harrington
Jessica R
JR
Cohen
Noah D
ND
Tsolis
Renee M
RM
Dangott
Lawrence J
LJ
Weinberg
Eugene D
ED
Martens
Ronald J
RJ
D001426:Bacterial Proteins / Q000235:genetics*; D003470:Culture Media; D003676:Deferoxamine / Q000494:pharmacology; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D007501:Iron / Q000494:pharmacology*; D008074:Lipoproteins / Q000235:genetics*; D016929:Rhodococcus equi / Q000187:drug effects / Q000235:genetics / Q000254:growth & development*; D014774:Virulence; D037521:Virulence Factors / Q000235:genetics*
D001426:Bacterial Proteins; D003470:Culture Media; D008074:Lipoproteins; D037521:Virulence Factors; D007501:Iron; D003676:Deferoxamine