scholarly journals Polymorphonuclear Leukocytes Restrict Growth of Pseudomonas aeruginosa in the Lungs of Cystic Fibrosis Patients

2014 ◽  
Vol 82 (11) ◽  
pp. 4477-4486 ◽  
Author(s):  
Kasper N. Kragh ◽  
Morten Alhede ◽  
Peter Ø. Jensen ◽  
Claus Moser ◽  
Thomas Scheike ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Pseudomonas Aeruginosa ◽  
Growth Rates ◽  
Polymorphonuclear Leukocytes ◽  
Growth Patterns ◽  
Tissue Samples ◽  
Content Type ◽  
Growth Physiology

ABSTRACTCystic fibrosis (CF) patients have increased susceptibility to chronic lung infections byPseudomonas aeruginosa, but the ecophysiology within the CF lung during infections is poorly understood. The aim of this study was to elucidate thein vivogrowth physiology ofP. aeruginosawithin lungs of chronically infected CF patients. A novel, quantitative peptide nucleic acid (PNA) fluorescencein situhybridization (PNA-FISH)-based method was used to estimate thein vivogrowth rates ofP. aeruginosadirectly in lung tissue samples from CF patients and the growth rates ofP. aeruginosain infected lungs in a mouse model. The growth rate ofP. aeruginosawithin CF lungs did not correlate with the dimensions of bacterial aggregates but showed an inverse correlation to the concentration of polymorphonuclear leukocytes (PMNs) surrounding the bacteria. A growth-limiting effect onP. aeruginosaby PMNs was also observedin vitro, where this limitation was alleviated in the presence of the alternative electron acceptor nitrate. The finding thatP. aeruginosagrowth patterns correlate with the number of surrounding PMNs points to a bacteriostatic effect by PMNs via their strong O2consumption, which slows the growth ofP. aeruginosain infected CF lungs. In support of this, the growth ofP. aeruginosawas significantly higher in the respiratory airways than in the conducting airways of mice. These results indicate a complex host-pathogen interaction in chronicP. aeruginosainfection of the CF lung whereby PMNs slow the growth of the bacteria and render them less susceptible to antibiotic treatment while enabling them to persist by anaerobic respiration.

scholarly journals Disruption of Cross-Feeding Inhibits Pathogen Growth in the Sputa of Patients with Cystic Fibrosis

mSphere ◽  
2020 ◽  
Vol 5 (2) ◽  
Author(s):  
Jeffrey M. Flynn ◽  
Lydia C. Cameron ◽  
Talia D. Wiggen ◽  
Jordan M. Dunitz ◽  
William R. Harcombe ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Pseudomonas Aeruginosa ◽  
Antibiotic Susceptibility ◽  
Susceptibility Testing ◽  
Anaerobic Bacteria ◽  
Content Type ◽  
Growth Environment ◽  
Polymicrobial Infections

ABSTRACT A critical limitation in the management of chronic polymicrobial infections is the lack of correlation between antibiotic susceptibility testing (AST) and patient responses to therapy. Underlying this disconnect is our inability to accurately recapitulate the in vivo environment and complex polymicrobial communities in vitro. However, emerging evidence suggests that, if modeled and tested accurately, interspecies relationships can be exploited by conventional antibiotics predicted to be ineffective by standard AST. As an example, under conditions where Pseudomonas aeruginosa relies on cocolonizing organisms for nutrients (i.e., cross-feeding), multidrug-resistant P. aeruginosa may be indirectly targeted by inhibiting the growth of its metabolic partners. While this has been shown in vitro using synthetic bacterial communities, the efficacy of a “weakest-link” approach to controlling host-associated polymicrobial infections has not yet been demonstrated. To test whether cross-feeding inhibition can be leveraged in clinically relevant contexts, we collected sputa from cystic fibrosis (CF) subjects and used enrichment culturing to isolate both P. aeruginosa and anaerobic bacteria from each sample. Predictably, both subpopulations showed various antibiotic susceptibilities when grown independently. However, when P. aeruginosa was cultured and treated under cooperative conditions in which it was dependent on anaerobic bacteria for nutrients, the growth of both the pathogen and the anaerobe was constrained despite their intrinsic antibiotic resistance profiles. These data demonstrate that the control of complex polymicrobial infections may be achieved by exploiting obligate or facultative interspecies relationships. Toward this end, in vitro susceptibility testing should evolve to more accurately reflect in vivo growth environments and microbial interactions found within them. IMPORTANCE Antibiotic efficacy achieved in vitro correlates poorly with clinical outcomes after treatment of chronic polymicrobial diseases; if a pathogen demonstrates susceptibility to a given antibiotic in the lab, that compound is often ineffective when administered clinically. Conversely, if a pathogen is resistant in vitro, patient treatment with that same compound can elicit a positive response. This discordance suggests that the in vivo growth environment impacts pathogen antibiotic susceptibility. Indeed, here we demonstrate that interspecies relationships among microbiotas in the sputa of cystic fibrosis patients can be targeted to indirectly inhibit the growth of Pseudomonas aeruginosa. The therapeutic implication is that control of chronic lung infections may be achieved by exploiting obligate or facultative relationships among airway bacterial community members. This strategy is particularly relevant for pathogens harboring intrinsic multidrug resistance and is broadly applicable to chronic polymicrobial airway, wound, and intra-abdominal infections.

scholarly journals Studies of Pseudomonas aeruginosa Mutants Indicate Pyoverdine as the Central Factor in Inhibition of Aspergillus fumigatus Biofilm

2017 ◽  
Vol 200 (1) ◽  
Author(s):  
Gabriele Sass ◽  
Hasan Nazik ◽  
John Penner ◽  
Hemi Shah ◽  
Shajia Rahman Ansari ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Pseudomonas Aeruginosa ◽  
Aspergillus Fumigatus ◽  
Fungal Pathogens ◽  
Human Pathogens ◽  
Biofilm Growth ◽  
Content Type ◽  
Iron Deprivation

ABSTRACT Pseudomonas aeruginosa and Aspergillus fumigatus are common opportunistic bacterial and fungal pathogens, respectively. They often coexist in airways of immunocompromised patients and individuals with cystic fibrosis, where they form biofilms and cause acute and chronic illnesses. Hence, the interactions between them have long been of interest and it is known that P. aeruginosa can inhibit A. fumigatus in vitro. We have approached the definition of the inhibitory P. aeruginosa molecules by studying 24 P. aeruginosa mutants with various virulence genes deleted for the ability to inhibit A. fumigatus biofilms. The ability of P. aeruginosa cells or their extracellular products produced during planktonic or biofilm growth to affect A. fumigatus biofilm metabolism or planktonic A. fumigatus growth was studied in agar and liquid assays using conidia or hyphae. Four mutants, the pvdD pchE, pvdD, lasR rhlR, and lasR mutants, were shown to be defective in various assays. This suggested the P. aeruginosa siderophore pyoverdine as the key inhibitory molecule, although additional quorum sensing-regulated factors likely contribute to the deficiency of the latter two mutants. Studies of pure pyoverdine substantiated these conclusions and included the restoration of inhibition by the pyoverdine deletion mutants. A correlation between the concentration of pyoverdine produced and antifungal activity was also observed in clinical P. aeruginosa isolates derived from lungs of cystic fibrosis patients. The key inhibitory mechanism of pyoverdine was chelation of iron and denial of iron to A. fumigatus. IMPORTANCE Interactions between human pathogens found in the same body locale are of vast interest. These interactions could result in exacerbation or amelioration of diseases. The bacterium Pseudomonas aeruginosa affects the growth of the fungus Aspergillus fumigatus. Both pathogens form biofilms that are resistant to therapeutic drugs and host immunity. P. aeruginosa and A. fumigatus biofilms are found in vivo, e.g., in the lungs of cystic fibrosis patients. Studying 24 P. aeruginosa mutants, we identified pyoverdine as the major anti-A. fumigatus compound produced by P. aeruginosa. Pyoverdine captures iron from the environment, thus depriving A. fumigatus of a nutrient essential for its growth and metabolism. We show how microbes of different kingdoms compete for essential resources. Iron deprivation could be a therapeutic approach to the control of pathogen growth.

scholarly journals Use of a Multiplex Transcript Method for Analysis of Pseudomonas aeruginosa Gene Expression Profiles in the Cystic Fibrosis Lung

2016 ◽  
Vol 84 (10) ◽  
pp. 2995-3006 ◽  
Author(s):  
Alex H. Gifford ◽  
Sven D. Willger ◽  
Emily L. Dolben ◽  
Lisa A. Moulton ◽  
Dana B. Dorman ◽  
...  
Keyword(s):  
Gene Expression ◽  
Cystic Fibrosis ◽  
Pseudomonas Aeruginosa ◽  
Expression Profiles ◽  
Clinical Isolates ◽  
Probe Design ◽  
Content Type ◽  
Lung Infections

The discovery of therapies that modulatePseudomonas aeruginosavirulence or that can eradicate chronicP. aeruginosalung infections associated with cystic fibrosis (CF) will be advanced by an improved understanding ofP. aeruginosabehaviorin vivo. We demonstrate the use of multiplexed Nanostring technology to monitor relative abundances ofP. aeruginosatranscripts across clinical isolates, in serial samples, and for the purposes of comparing microbial physiologyin vitroandin vivo. The expression of 75 transcripts encoded by genes implicated in CF lung disease was measured in a variety ofP. aeruginosastrains as well as RNA serial sputum samples from fourP. aeruginosa-colonized subjects with CF collected over 6 months. We present data on reproducibility, the results from different methods of normalization, and demonstrate high concordance between transcript relative abundance data obtained by Nanostring or transcriptome sequencing (RNA-Seq) analysis. Furthermore, we address considerations regarding sequence variation between strains during probe design. Analysis ofP. aeruginosagrownin vitroidentified transcripts that correlated with the different phenotypes commonly observed in CF clinical isolates.P. aeruginosatranscript profiles in RNA from CF sputum indicated alginate productionin vivo, and transcripts involved in quorum-sensing regulation were less abundant in sputum than strains grown in the laboratory.P. aeruginosagene expression patterns from sputum clustered closely together relative to patterns for laboratory-grown cultures; in contrast, laboratory-grownP. aeruginosashowed much greater transcriptional variation with only loose clustering of strains with different phenotypes. The clustering within and between subjects was surprising in light of differences in inhaled antibiotic and respiratory symptoms, suggesting that the pathways represented by these 75 transcripts are stable in chronic CFP. aeruginosalung infections.

scholarly journals Evolution of the Pseudomonas aeruginosa Aminoglycoside Mutational Resistome In Vitro and in the Cystic Fibrosis Setting

2018 ◽  
Vol 62 (4) ◽  
Author(s):  
Carla López-Causapé ◽  
Rosa Rubio ◽  
Gabriel Cabot ◽  
Antonio Oliver
Keyword(s):  
Cystic Fibrosis ◽  
Pseudomonas Aeruginosa ◽  
Respiratory Infections ◽  
Aminoglycoside Resistance ◽  
Resistance Development ◽  
Content Type ◽  
High Doses ◽  
High Level

ABSTRACT Inhaled administration of high doses of aminoglycosides is a key maintenance treatment of Pseudomonas aeruginosa chronic respiratory infections in cystic fibrosis (CF). We analyzed the dynamics and mechanisms of stepwise high-level tobramycin resistance development in vitro and compared the results with those of isogenic pairs of susceptible and resistant clinical isolates. Resistance development correlated with fusA1 mutations in vitro and in vivo. pmrB mutations, conferring polymyxin resistance, were also frequently selected in vitro . In contrast, mutational overexpression of MexXY, a hallmark of aminoglycoside resistance in CF, was not observed in in vitro evolution experiments.

scholarly journals Exogenous Alginate Protects Staphylococcus aureus from Killing by Pseudomonas aeruginosa

2019 ◽  
Vol 202 (8) ◽  
Author(s):  
Courtney E. Price ◽  
Dustin G. Brown ◽  
Dominique H. Limoli ◽  
Vanessa V. Phelan ◽  
George A. O’Toole
Keyword(s):  
Staphylococcus Aureus ◽  
Pseudomonas Aeruginosa ◽  
Physical Space ◽  
Late Time ◽  
Protective Effects ◽  
Content Type ◽  
Alginate Production ◽  
The Impact

ABSTRACT Cystic fibrosis (CF) patients chronically infected with both Pseudomonas aeruginosa and Staphylococcus aureus have worse health outcomes than patients who are monoinfected with either P. aeruginosa or S. aureus. We showed previously that mucoid strains of P. aeruginosa can coexist with S. aureus in vitro due to the transcriptional downregulation of several toxic exoproducts typically produced by P. aeruginosa, including siderophores, rhamnolipids, and HQNO (2-heptyl-4-hydroxyquinoline N-oxide). Here, we demonstrate that exogenous alginate protects S. aureus from P. aeruginosa in both planktonic and biofilm coculture models under a variety of nutritional conditions. S. aureus protection in the presence of exogenous alginate is due to the transcriptional downregulation of pvdA, a gene required for the production of the iron-scavenging siderophore pyoverdine as well as the downregulation of the PQS (Pseudomonas quinolone signal) (2-heptyl-3,4-dihydroxyquinoline) quorum sensing system. The impact of exogenous alginate is independent of endogenous alginate production. We further demonstrate that coculture of mucoid P. aeruginosa with nonmucoid P. aeruginosa strains can mitigate the killing of S. aureus by the nonmucoid strain of P. aeruginosa, indicating that the mechanism that we describe here may function in vivo in the context of mixed infections. Finally, we investigated a panel of mucoid clinical isolates that retain the ability to kill S. aureus at late time points and show that each strain has a unique expression profile, indicating that mucoid isolates can overcome the S. aureus-protective effects of mucoidy in a strain-specific manner. IMPORTANCE CF patients are chronically infected by polymicrobial communities. The two dominant bacterial pathogens that infect the lungs of CF patients are P. aeruginosa and S. aureus, with ∼30% of patients coinfected by both species. Such coinfected individuals have worse outcomes than monoinfected patients, and both species persist within the same physical space. A variety of host and environmental factors have been demonstrated to promote P. aeruginosa-S. aureus coexistence, despite evidence that P. aeruginosa kills S. aureus when these organisms are cocultured in vitro. Thus, a better understanding of P. aeruginosa-S. aureus interactions, particularly mechanisms by which these microorganisms are able to coexist in proximal physical space, will lead to better-informed treatments for chronic polymicrobial infections.

scholarly journals Within-Host Evolution of Pseudomonas aeruginosa Reveals Adaptation toward Iron Acquisition from Hemoglobin

mBio ◽  
2014 ◽  
Vol 5 (3) ◽  
Author(s):  
Rasmus Lykke Marvig ◽  
Søren Damkiær ◽  
S. M. Hossein Khademi ◽  
Trine M. Markussen ◽  
Søren Molin ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Pseudomonas Aeruginosa ◽  
Iron Acquisition ◽  
Chronic Infections ◽  
Content Type ◽  
Mortality And Morbidity ◽  
Airway Infections ◽  
Host Evolution ◽  
Promoter Mutations

ABSTRACTPseudomonas aeruginosaairway infections are a major cause of mortality and morbidity of cystic fibrosis (CF) patients. In order to persist,P. aeruginosadepends on acquiring iron from its host, and multiple different iron acquisition systems may be active during infection. This includes the pyoverdine siderophore and thePseudomonasheme utilization (phu) system. While the regulation and mechanisms of several iron-scavenging systems are well described, it is not clear whether such systems are targets for selection during adaptation ofP. aeruginosato the host environment. Here we investigated the within-host evolution of the transmissibleP. aeruginosaDK2 lineage. We found positive selection for promoter mutations leading to increased expression of thephusystem. By mimicking conditions of the CF airwaysin vitro, we experimentally demonstrate that increased expression ofphuRconfers a growth advantage in the presence of hemoglobin, thus suggesting thatP. aeruginosaevolves toward iron acquisition from hemoglobin. To rule out that this adaptive trait is specific to the DK2 lineage, we inspected the genomes of additionalP. aeruginosalineages isolated from CF airways and found similar adaptive evolution in two distinct lineages (DK1 and PA clone C). Furthermore, in all three lineages,phuRpromoter mutations coincided with the loss of pyoverdine production, suggesting that within-host adaptation toward heme utilization is triggered by the loss of pyoverdine production. Targeting heme utilization might therefore be a promising strategy for the treatment ofP. aeruginosainfections in CF patients.IMPORTANCEMost bacterial pathogens depend on scavenging iron within their hosts, which makes the battle for iron between pathogens and hosts a hallmark of infection. Accordingly, the ability of the opportunistic pathogenPseudomonas aeruginosato cause chronic infections in cystic fibrosis (CF) patients also depends on iron-scavenging systems. While the regulation and mechanisms of several such iron-scavenging systems have been well described, not much is known about how the within-host selection pressures act on the pathogens’ ability to acquire iron. Here, we investigated the within-host evolution ofP. aeruginosa, and we found evidence thatP. aeruginosaduring long-term infections evolves toward iron acquisition from hemoglobin. This adaptive strategy might be due to a selective loss of other iron-scavenging mechanisms and/or an increase in the availability of hemoglobin at the site of infection. This information is relevant to the design of novel CF therapeutics and the development of models of chronic CF infections.

scholarly journals Type-4 Phosphodiesterase (PDE4) Blockade Reduces NETosis in Cystic Fibrosis

2021 ◽  
Vol 12 ◽  
Author(s):  
Licia Totani ◽  
Concetta Amore ◽  
Antonio Piccoli ◽  
Giuseppe Dell’Elba ◽  
Angelo Di Santo ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Pseudomonas Aeruginosa ◽  
Lung Disease ◽  
Pde4 Inhibitor ◽  
Free Dna ◽  
Impaired Lung Function ◽  
Cellular Integrity ◽  
Net Release

Neutrophilic inflammation is a key determinant of cystic fibrosis (CF) lung disease. Neutrophil-derived free DNA, released in the form of extracellular traps (NETs), significantly correlates with impaired lung function in patients with CF, underlying their pathogenetic role in CF lung disease. Thus, specific approaches to control NETosis of neutrophils migrated into the lungs may be clinically relevant in CF. We investigated the efficacy of phosphodiesterase (PDE) type-4 inhibitors, in vitro, on NET release by neutrophils from healthy volunteers and individuals with CF, and in vivo, on NET accumulation and lung inflammation in mice infected with Pseudomonas aeruginosa. PDE4 blockade curbed endotoxin-induced NET production and preserved cellular integrity and apoptosis in neutrophils, from healthy subjects and patients with CF, challenged with endotoxin, in vitro. The pharmacological effects of PDE4 inhibitors were significantly more evident on CF neutrophils. In a mouse model of Pseudomonas aeruginosa chronic infection, aerosol treatment with roflumilast, a selective PDE4 inhibitor, gave a significant reduction in free DNA in the BALF. This was accompanied by reduced citrullination of histone H3 in neutrophils migrated into the airways. Roflumilast-treated mice showed a significant improvement in weight recovery. Our study provides the first evidence that PDE4 blockade controls NETosis in vitro and in vivo, in CF-relevant models. Since selective PDE4 inhibitors have been recently approved for the treatment of COPD and psoriasis, our present results encourage clinical trials to test the efficacy of this class of drugs in CF.

scholarly journals Genomic Analysis Identifies NovelPseudomonas aeruginosaResistance Genes under Selection during Inhaled Aztreonam TherapyIn Vivo

2019 ◽  
Vol 63 (9) ◽  
Author(s):  
Kathryn McLean ◽  
Duankun Lee ◽  
Elizabeth A. Holmes ◽  
Kelsi Penewit ◽  
Adam Waalkes ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Positive Selection ◽  
Single Gene ◽  
Genomic Analysis ◽  
Maximal Activity ◽  
Content Type ◽  
Cystic Fibrosis Airway ◽  
Bacterial Fitness

ABSTRACTInhaled aztreonam is increasingly used for chronicPseudomonas aeruginosasuppression in patients with cystic fibrosis (CF), but the potential for that organism to evolve aztreonam resistance remains incompletely explored. Here, we performed genomic analysis of clonally related pre- and posttreatment CF clinical isolate pairs to identify genes that are under positive selection during aztreonam therapyin vivo. We identified 16 frequently mutated genes associated with aztreonam resistance, the most prevalent beingftsIandampC, and 13 of which increased aztreonam resistance when introduced as single gene transposon mutants. Several previously implicated aztreonam resistance genes were found to be under positive selection in clinical isolates even in the absence of inhaled aztreonam exposure, indicating that other selective pressures in the cystic fibrosis airway can promote aztreonam resistance. Given its potential to confer plasmid-mediated resistance, we further characterized mutantampCalleles and performed artificial evolution ofampCfor maximal activity against aztreonam. We found that naturally occurringampCmutants conferred variably increased resistance to aztreonam (2- to 64-fold) and other β-lactam agents but that its maximal evolutionary capacity for hydrolyzing aztreonam was considerably higher (512- to 1,024-fold increases) and was achieved while maintaining or increasing resistance to other drugs. These studies implicate novel chromosomal aztreonam resistance determinants while highlighting that different mutations are favored during selectionin vivoandin vitro, show thatampChas a high maximal potential to hydrolyze aztreonam, and provide an approach to disambiguate mutations promoting specific resistance phenotypes from those more generally increasing bacterial fitnessin vivo.

Pseudomonas aeruginosa tolerance to tobramycin, hydrogen peroxide and polymorphonuclear leukocytes is quorum-sensing dependent

Microbiology ◽  
2005 ◽  
Vol 151 (2) ◽  
pp. 373-383 ◽  
Author(s):  
Thomas Bjarnsholt ◽  
Peter Østrup Jensen ◽  
Mette Burmølle ◽  
Morten Hentzer ◽  
Janus A. J. Haagensen ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Quorum Sensing ◽  
Polymorphonuclear Leukocytes ◽  
Present Report ◽  
Cell Communication ◽  
A Cell ◽  
Opportunistic Human Pathogen ◽  
Conventional Antibiotics

The opportunistic human pathogen Pseudomonas aeruginosa is the predominant micro-organism of chronic lung infections in cystic fibrosis (CF) patients. P. aeruginosa colonizes the CF lungs by forming biofilm structures in the alveoli. In the biofilm mode of growth the bacteria are highly tolerant to otherwise lethal doses of antibiotics and are protected from bactericidal activity of polymorphonuclear leukocytes (PMNs). P. aeruginosa controls the expression of many of its virulence factors by means of a cell–cell communication system termed quorum sensing (QS). In the present report it is demonstrated that biofilm bacteria in which QS is blocked either by mutation or by administration of QS inhibitory drugs are sensitive to treatment with tobramycin and H2O2, and are readily phagocytosed by PMNs, in contrast to bacteria with functional QS systems. In contrast to the wild-type, QS-deficient biofilms led to an immediate respiratory-burst activation of the PMNs in vitro. In vivo QS-deficient mutants provoked a higher degree of inflammation. It is suggested that quorum signals and QS-inhibitory drugs play direct and opposite roles in this process. Consequently, the faster and highly efficient clearance of QS-deficient bacteria in vivo is probably a two-sided phenomenon: down regulation of virulence and activation of the innate immune system. These data also suggest that a combination of the action of PMNs and QS inhibitors along with conventional antibiotics would eliminate the biofilm-forming bacteria before a chronic infection is established.

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

mBio ◽  
2013 ◽  
Vol 4 (4) ◽  
Author(s):  
Ryan C. Hunter ◽  
Fadi Asfour ◽  
Jozef Dingemans ◽  
Brenda L. Osuna ◽  
Tahoura Samad ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Ferrous Iron ◽  
Ferric Iron ◽  
Relative Proportion ◽  
Iron Oxidation ◽  
The United States ◽  
Environmental Parameter ◽  
Content Type

ABSTRACTChronic, biofilm-like infections by the opportunistic pathogenPseudomonas aeruginosaare a major cause of mortality in cystic fibrosis (CF) patients. While much is known aboutP. aeruginosafrom laboratory studies, far less is understood about what it experiencesin vivo. Iron is an important environmental parameter thought to play a central role in the development and maintenance ofP. aeruginosainfections, 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 theP. aeruginosagenesbqsRS, 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 byP. aeruginosain various oxicin vitrosystems, 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.IMPORTANCEIron 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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