Pseudomonas aeruginosa Uses Multiple Pathways To Acquire Iron during Chronic Infection in Cystic Fibrosis Lungs

Abstract

ABSTRACTPseudomonas aeruginosachronically infects the lungs of more than 80% of adult patients with cystic fibrosis (CF) and is a major contributor to the progression of disease pathology.P. aeruginosarequires iron for growth and has multiple iron uptake systems that have been studied in bacteria grown in laboratory culture. The purpose of this research was to determine which of these are active during infection in CF. RNA was extracted from 149 sputum samples obtained from 23 CF patients. Reverse transcription–quantitative real-time PCR (RT-qPCR) was used to measure the expression ofP. aeruginosagenes encoding transport systems for the siderophores pyoverdine and pyochelin, for heme, and for ferrous ions. Expression ofP. aeruginosagenes could be quantified in 89% of the sputum samples. Expression of genes associated with siderophore-mediated iron uptake was detected in most samples but was at low levels in some samples, indicating that other iron uptake mechanisms are active. Expression of genes encoding heme transport systems was also detected in most samples, indicating that heme uptake occurs during infection in CF.feoBexpression was detected in all sputum samples, implying an important role for ferrous ion uptake byP. aeruginosain CF. Our data show that multipleP. aeruginosairon uptake mechanisms are active in chronic CF infection and that RT-qPCR of RNA extracted from sputum provides a powerful tool for investigating bacterial physiology during infection in CF.