Iron-binding compounds impair Pseudomonas aeruginosa biofilm formation, especially under anaerobic conditions

Abstract

The success of Pseudomonas aeruginosa in cystic fibrosis (CF) and other chronic infections is largely attributed to its ability to grow in antibiotic-resistant biofilm communities. This study investigated the effects of limiting iron levels as a strategy for preventing/disrupting P. aeruginosa biofilms. A range of synthetic and naturally occurring iron-chelating agents were examined. Biofilm development by P. aeruginosa strain PAO1 and CF sputum isolates from chronically infected individuals was significantly decreased by iron removal under aerobic atmospheres. CF strains formed poor biofilms under anaerobic conditions. Strain PAO1 was also tested under anaerobic conditions. Biofilm formation by this model strain was almost totally prevented by several of the chelators tested. The ability of synthetic chelators to impair biofilm formation could be reversed by iron addition to cultures, providing evidence that these effective chelating compounds functioned by directly reducing availability of iron to P. aeruginosa. In contrast, the biological chelator lactoferrin demonstrated enhanced anti-biofilm effects as iron supplementation increased. Hence biofilm inhibition by lactoferrin appeared to occur through more complex mechanisms to those of the synthetic chelators. Overall, our results demonstrate the importance of iron availability to biofilms and that iron chelators have potential as adjunct therapies for preventing biofilm development, especially under low oxygen conditions such as encountered in the chronically infected CF lung.

The Urinary Antibiotic 5-Nitro-8-Hydroxyquinoline (Nitroxoline) Reduces the Formation and Induces the Dispersal of Pseudomonas aeruginosa Biofilms by Chelation of Iron and Zinc

“…Interestingly, the basal half of the biofilm layer appeared to remain unaffected by nitroxoline. Similar results were previously reported by O'May et al, who demonstrated a substantial mass but not a surface reduction by exposure of mature PAO1 biofilms to high dosages of the iron chelator 2,29-dipyridyl (about a twothird decrease in thickness at 2,500 M) (19).…”

“…Its activity is comparable to that reported for EDTA (1,19), but it is orally applicable, less toxic, and the antibiofilm effect was obtained at concentrations that are in the range achieved in vivo during oral nitroxoline treatment (plasma peak levels of approximately 6 mg/liter and persistent urine levels around 300 mg/liter) (2). In contrast to lactoferrin and the related egg white-derived conalbumin, it is a synthetic, relatively cheap compound, without additional immunomodulating functions and far lesser allergenic potential.…”

“…Maintenance of these complex bacterial communities is a dynamic process that has previously been shown to be regulated by various divalent cations, including Fe 2ϩ , Zn 2ϩ , Mg 2ϩ , and Ca 2ϩ (3,5,21,22). Currently, attempts are under way to identify therapeutically applicable compounds that would show strong chelating properties without concomitant immunogenicity or toxicity (1,18,19). The antimicrobial effects of the urinary antibiotic nitroxoline have long been known to depend on its ability to chelate bivalent and trivalent cations (9,20).…”

The Haemophilus influenzae Sap Transporter Mediates Bacterium-Epithelial Cell Homeostasis

“…The importance of biofilm formation in the resistance to antimicrobial peptides and antibiotic therapy has been well established, and it contributes to persistence in the host (31,57,58). In addition, biofilm formation is influenced by host microenvironments that are limited in available iron, which is particularly important as the host sequesters free iron as a means to limit bacterial growth (59)(60)(61)(62)(63)(64)(65)(66)(67). We have demonstrated that transient restriction of heme iron enhances biofilm structural complexity and peak height in wild-type NTHI (B. R. Szelestey and K. M. Mason, unpublished observations).…”

Bacillus cereus growth and biofilm formation: the impact of substratum, iron sources, and transcriptional regulator Sigma 54

“…The latter is surprising in relation to previous reports of inhibition and even disruption of Pseudomonas biofilms by lactoferrin (Singh et al 2002, Kamiya et al 2012). The anti-biofilm effect of lactoferrin was apparently not simply due to iron removal since increasing concentrations of iron in the presence of lactoferrin increased its anti-biofilm activity (O'May et al 2009). …”