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Ferrous Iron Is a Significant Component of Bioavailable Iron in Cystic Fibrosis Airways

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      ABSTRACT

      Chronic, biofilm-like infections by the opportunistic pathogen Pseudomonas aeruginosa are a major cause of mortality in cystic fibrosis (CF) patients. While much is known about P. aeruginosa from laboratory studies, far less is understood about what it experiences in vivo. Iron is an important environmental parameter thought to play a central role in the development and maintenance of P. aeruginosa infections, for both anabolic and signaling purposes. Previous studies have focused on ferric iron [Fe(III)] as a target for antimicrobial therapies; however, here we show that ferrous iron [Fe(II)] is abundant in the CF lung (~39 µM on average for severely sick patients) and significantly correlates with disease severity (ρ = −0.56, P = 0.004), whereas ferric iron does not (ρ = −0.28, P = 0.179). Expression of the P. aeruginosa genes bqsRS, whose transcription is upregulated in response to Fe(II), was high in the majority of patients tested, suggesting that increased Fe(II) is bioavailable to the infectious bacterial population. Because limiting Fe(III) acquisition inhibits biofilm formation by P. aeruginosa in various oxic in vitro systems, we also tested whether interfering with Fe(II) acquisition would improve biofilm control under anoxic conditions; concurrent sequestration of both iron oxidation states resulted in a 58% reduction in biofilm accumulation and 28% increase in biofilm dissolution, a significant improvement over Fe(III) chelation treatment alone. This study demonstrates that the chemistry of infected host environments coevolves with the microbial community as infections progress, which should be considered in the design of effective treatment strategies at different stages of disease.

      IMPORTANCE

      Iron is an important environmental parameter that helps pathogens thrive in sites of infection, including those of cystic fibrosis (CF) patients. Ferric iron chelation therapy has been proposed as a novel therapeutic strategy for CF lung infections, yet until now, the iron oxidation state has not been measured in the host. In studying mucus from the infected lungs of multiple CF patients from Europe and the United States, we found that ferric and ferrous iron change in concentration and relative proportion as infections progress; over time, ferrous iron comes to dominate the iron pool. This information is relevant to the design of novel CF therapeutics and, more broadly, to developing accurate models of chronic CF infections.

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      Most cited references 54

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      Analysis of relative gene expression data using real-time quantitative PCR and the 2(-Delta Delta C(T)) Method.

       K Livak,  T Schmittgen (2001)
      The two most commonly used methods to analyze data from real-time, quantitative PCR experiments are absolute quantification and relative quantification. Absolute quantification determines the input copy number, usually by relating the PCR signal to a standard curve. Relative quantification relates the PCR signal of the target transcript in a treatment group to that of another sample such as an untreated control. The 2(-Delta Delta C(T)) method is a convenient way to analyze the relative changes in gene expression from real-time quantitative PCR experiments. The purpose of this report is to present the derivation, assumptions, and applications of the 2(-Delta Delta C(T)) method. In addition, we present the derivation and applications of two variations of the 2(-Delta Delta C(T)) method that may be useful in the analysis of real-time, quantitative PCR data. Copyright 2001 Elsevier Science (USA).
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        Biofilms: Survival Mechanisms of Clinically Relevant Microorganisms

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          Biofilms: survival mechanisms of clinically relevant microorganisms.

          Though biofilms were first described by Antonie van Leeuwenhoek, the theory describing the biofilm process was not developed until 1978. We now understand that biofilms are universal, occurring in aquatic and industrial water systems as well as a large number of environments and medical devices relevant for public health. Using tools such as the scanning electron microscope and, more recently, the confocal laser scanning microscope, biofilm researchers now understand that biofilms are not unstructured, homogeneous deposits of cells and accumulated slime, but complex communities of surface-associated cells enclosed in a polymer matrix containing open water channels. Further studies have shown that the biofilm phenotype can be described in terms of the genes expressed by biofilm-associated cells. Microorganisms growing in a biofilm are highly resistant to antimicrobial agents by one or more mechanisms. Biofilm-associated microorganisms have been shown to be associated with several human diseases, such as native valve endocarditis and cystic fibrosis, and to colonize a wide variety of medical devices. Though epidemiologic evidence points to biofilms as a source of several infectious diseases, the exact mechanisms by which biofilm-associated microorganisms elicit disease are poorly understood. Detachment of cells or cell aggregates, production of endotoxin, increased resistance to the host immune system, and provision of a niche for the generation of resistant organisms are all biofilm processes which could initiate the disease process. Effective strategies to prevent or control biofilms on medical devices must take into consideration the unique and tenacious nature of biofilms. Current intervention strategies are designed to prevent initial device colonization, minimize microbial cell attachment to the device, penetrate the biofilm matrix and kill the associated cells, or remove the device from the patient. In the future, treatments may be based on inhibition of genes involved in cell attachment and biofilm formation.
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            Author and article information

            Affiliations
            Division of Biology [ a ]
            Division of Geological and Planetary Sciences [ b ]
            Howard Hughes Medical Institute, [ c ] California Institute of Technology, Pasadena, California, USA
            Department of Pediatric Pulmonology, Children’s Hospital of Los Angeles, Los Angeles, California, USA [ d ]
            Department of Bioengineering Sciences, Research Group Microbiology, Flanders Interuniversity Institute of Biotechnology (VIB), Vrije Universiteit Brussel, Brussels, Belgium [ e ]
            Unit of Microbiology, Expert Group Molecular and Cellular Biology, Institute for Environment, Health and Safety, Belgian Nuclear Research Centre (SCK CEN), Mol, Belgium [ f ]
            Statistical Consulting, Information Technology Services, University of Southern California, Los Angeles, California, USA [ g ]
            Cystic Fibrosis Clinic, Universitair Ziekenhuis Brussel (UZB), Brussels, Belgium [ h ]
            Author notes
            Address correspondence to Dianne K. Newman, dkn@ 123456caltech.edu .

            Editor Arturo Casadevall, Albert Einstein College of Medicine

            Journal
            mBio
            MBio
            mbio
            mbio
            mBio
            mBio
            American Society of Microbiology (1752 N St., N.W., Washington, DC )
            2150-7511
            20 August 2013
            Jul-Aug 2013
            : 4
            : 4
            23963183 3753050 mBio00557-13 10.1128/mBio.00557-13
            Copyright © 2013 Hunter et al.

            This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-ShareAlike 3.0 Unported license, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original author and source are credited.

            Counts
            Pages: 8
            Categories
            Research Article
            Custom metadata
            July/August 2013

            Life sciences

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