Iron Availability Influences Aggregation, Biofilm, Adhesion and Invasion of Pseudomonas Aeruginosa and Burkholderia Cenocepacia

Abstract

Pseudomonas aeruginosa and Burkholderia cenocepacia are predominant opportunistic pathogens in cystic fibrosis (CF) patients. In healthy humans the lower respiratory tract as well as all mucosa, contains a very low free iron concentration (10-18 M), while in CF patients' sputum iron concentration is very high, showing a median value of 63x10-6 M. Accumulation of catalytic reactive iron heavily contributes to subsequent clinical complications in the lung disorders by the production of reactive oxygen species and increases bacterial growth and virulence. The data reported in this study indicate that low iron concentration (Fe 3 + 1 JA.M) induced free-living forms and motility both in P. aeruginosa and B. cenocepacia, while high iron concentrations (Fe 3 + 10 and 100 tJ.M) stimulated aggregation and biofilm formation already in the fluid phases, so demonstrating that aggregation and biofllm formation are positively iron-modulated in these bacteria. Moreover, the different morphological forms (free-living, aggregates and biofllm) showed different capabilities of adhering and invading the bronchial cell line A549. P. aeruginosa PA01 aggregates, and mostly biofllm, exerted the highest adhesion efficiency, while B. cenocepacia PV1 aggregates or biofilm the lowest. A significant reduction in invasion efficiency by P. aeruginosa biofilm and a significant increase in cell internalization by B. cenocepacia biofllm has been reported. Therefore, the iron availability is an important signal to which P. aeruginosa and B. cenocepacia counteract by leaving the motile free-living forms and entering into a new lifestyle, i.e, biofllm. These data could contribute to explain that the ironoverload of the sputum of CF patients, inducing nonmotile forms, aggregates and biofllm, may facilitate penetration of host epithelial barriers contributing to the establishment of infection, colonization, persistence and systemic spread of these opportunistic pathogens.Pseudomonas aeruginosa is a ubiquitous Gramnegative motile bacterium found in different environments such as soil, freshwater and marine habitat. Moreover, P. aeruginosa is the predominant opportunistic pathogen in cystic fibrosis (CF) patients, as the lungs of >90% of all CF patients are colonized by this bacterium (1). Chronic colonization of P. aeruginosa in CF patient airways is a major source of morbidity and mortality (2) leading to epithelial surface damage and airway plugging which results in a decrease of pulmonary function (3).Although not as prevalent as P. aeruginosa, Burkholderia cepacia is another important opportunistic respiratory pathogen in CF patients (2),

Bovine Lactoferrin Inhibits the Efficiency of Invasion of Respiratory A549 Cells of Different Iron-Regulated Morphological Forms of Pseudomonas Aeruginosa and Burkholderia Cenocepacia

“…Twitching is a specialized type of motility of bacteria that wander across the colonized surface instead of forming biofilm (2). Similar results were also reported for Burkholderia cenocepacia where motility inversely correlates with iron availability (3). Moreover, iron highly influences the morphological forms 'of both p. aeruginosa and B. cenocepacia, since different levels of iron availability induces bacteria to form aggregates or biofilm (3).…”

“…biofilm, in the respiratory tract of CF patients (6)(7). Furthermore, the ability of P. aeruginosa and B. cenocepacia to regulate their mode of growth (freeliving, aggregates and biofilm) depending on iron availability confers to these pathogens the chance to modulate their adhesion and invasion efficiency into host cells (3).…”

The transition metal gallium disrupts Pseudomonas aeruginosa iron metabolism and has antimicrobial and antibiofilm activity

“…The link between Fe and biofilm formation (9)(10)(11)(12) and the fact that Ga can disrupt Fe-dependent processes (21) led us to investigate the effect of Ga on P. aeruginosa biofilm development. Studying Ga's effects on biofilms was also of interest because low concentrations of a number of antibiotics promote biofilm formation, perhaps because biofilm growth can be induced as a consequence of stress (22)(23)(24)(25).…”

“…High levels of Fe are required for the formation of cell clusters early in biofilm development and for the maturation of biofilms into 3-dimensional structures (9)(10)(11)(12). Fe-withholding defenses may also be protective during infection, as bacteria taken from infection sites show gene expression profiles of Fe starvation (13)(14)(15).…”

Iron acquisition in the cystic fibrosis lung and potential for novel therapeutic strategies

“…There is a variety of evidence implicating iron acquisition in microbial pathogenesis. Over a decade ago, Berlutti et al (2005) demonstrated that iron availability impacts on biofilm formation, adhesion and invasion of two important CF pathogens, P. aeruginosa and Burkholderia cenocepacia. More recently, Wiens et al (2014) demonstrated that alginate production, mucoid phenotype and biofilm formation by P. aeruginosa are iron regulated.…”