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J Med Microbiol 56 (2007), 119-128; DOI: 10.1099/jmm.0.46844-0
© 2007 Society for General Microbiology
ISSN 1473-5644

Evaluation of different iron sources and their influence in biofilm formation by the dental pathogen Actinobacillus actinomycetemcomitans

Eric R. Rhodes1, Christopher J. Shoemaker1, Sharon M. Menke1, Richard E. Edelmann2 and Luis A. Actis1

1 Department of Microbiology, Miami University, Oxford, OH, USA

2 Department of Botany, Miami University, Oxford, OH, USA

Correspondence
Luis A. Actis
actisla{at}muohio.edu

Received 18 July 2006
Accepted 25 September 2006

Actinobacillus actinomycetemcomitans, a pathogen associated with oral and extra-oral infections, requires iron to grow under limiting conditions. Although incapable of producing siderophores, this pathogen could acquire iron by direct interaction with compounds such as haemin, haemoglobin, lactoferrin and transferrin. In this work the ability of different A. actinomycetemcomitans strains to bind and use different iron sources was tested. None of the strains tested used haemoglobin, lactoferrin or transferrin as sole sources of iron. However, all of them used FeCl3 and haemin as iron sources under chelated conditions. Dot-blot binding assays showed that all strains bind lactoferrin, haemoglobin and haemin, but not transferrin. Insertion inactivation of hmsF, which encodes a predicted cell-envelope protein related to haemin-storage proteins produced by other pathogens, reduced haemin and Congo red binding drastically without affecting haemin utilization as an iron source under chelated conditions. Biofilm assays showed that all strains tested attached to and formed biofilms on plastic under iron-rich and iron-chelated conditions. However, scanning electron microscopy showed that smooth strains formed simpler biofilms than rough isolates. Furthermore, the incubation of rough cells in the presence of FeCl3 or haemin resulted in the formation of more aggregates and microcolonies compared with the fewer cell aggregates formed when cells were grown in the presence of the synthetic iron chelator dipyridyl. These cell responses to changes in extracellular iron concentrations may reflect those that this pathogen expresses under the conditions it encounters in the human oral cavity.

Abbreviations: DIP, dipyridyl; DMB, 3,3'-dimethoxybenzidine dihydrochloride; HRP, horseradish peroxidase; LAP, localized aggressive periodontitis; SEM, scanning electron microscope/microscopy.






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