A recent study published in Frontiers in Microbiology has examined how iron levels influence the growth and virulence of Pseudomonas aeruginosa, a bacterium responsible for persistent lung infections. Researchers modeled various iron environments that mimic those found in chronic pulmonary infections to better understand the bacteria's behavior.
The research found that when P. aeruginosa is exposed to iron-rich laboratory conditions, it grows more readily and forms robust biofilms. However, this comes with a reduction in the production of key virulence factors, which results in less damage to host tissue. The findings highlight a trade-off: while iron supports bacterial persistence in the lungs, it simultaneously dampens the bacterium’s ability to cause severe disease.
P. aeruginosa is known as an opportunistic pathogen that can infect multiple body systems but poses particular challenges when it establishes chronic lung infections due to its capacity for biofilm formation. These biofilms help shield bacteria from treatments and immune responses.
The study tested both clinical isolates from persistent lung infections and a reference strain (PAO1) under varying iron concentrations using laboratory models simulating iron-replete and iron-deficient conditions. In iron-rich environments, all strains showed optimal growth and enhanced biofilm development compared to those grown under limited or partially restored iron conditions.
Despite this increased growth, bacteria cultured in iron-replete media produced significantly lower levels of virulence factors such as protease, pyocyanin, exotoxin A, phospholipase C, elastase, siderophores, and hemolysins than those grown with restricted or partially restored iron.
In infection models using Galleria mellonella larvae and mice, organisms pre-cultured under high-iron conditions resulted in higher survival rates for larvae and greater bacterial loads in mouse lungs but led to reduced inflammation markers and less tissue damage compared to those infected with bacteria grown under low-iron conditions.
Histological examination revealed that mice infected with P. aeruginosa from iron-rich cultures experienced minimal immune cell infiltration and mild changes in lung structure. In contrast, those infected with bacteria from low-iron environments had significant lung pathology including alveolar collapse, immune cell infiltration, edema, hemorrhage, and vascular congestion.
The researchers concluded that environmental iron availability shapes not only bacterial persistence but also the severity of infection by decoupling bacterial load from disease outcome. "This decoupling of bacterial burden from disease severity may help explain why P. aeruginosa establishes persistent lung infections that are treatment-resistant yet exhibit variable clinical outcomes."
The authors warn that strategies focusing solely on depriving bacteria of iron might worsen lung inflammation rather than reduce infection severity: "Therapeutic strategies aimed solely at iron deprivation could unintentionally exacerbate lung inflammation and tissue damage," they stated. They recommend future studies examine how manipulating lung iron levels impacts long-term outcomes for patients with chronic pulmonary infections.
