The lungs of patients with
cystic fibrosis become chronically infected with the bacterium Pseudomonas aeruginosa, which heralds progressive lung damage and a decline in health.
Iron is a crucial
micronutrient for bacteria and its acquisition is a key factor in
infection. P. aeruginosa can acquire this
element by secreting
pyoverdine and
pyochelin,
iron-chelating compounds (
siderophores) that scavenge
iron and deliver it to the bacteria.
Siderophore-mediated
iron uptake is generally considered a key factor in the ability of P. aeruginosa to cause
infection. We have investigated the amounts of
pyoverdine in 148 sputum samples from 36
cystic fibrosis patients (30 infected with P. aeruginosa and 6 as negative controls).
Pyoverdine was present in 93 samples in concentrations between 0.30 and 51 μM (median 4.6 μM) and there was a strong association between the amount of
pyoverdine and the number of P. aeruginosa present. However,
pyoverdine was not present, or below the limits of detection (~0.3 μM), in 21 sputum samples that contained P. aeruginosa.
Pyochelin was also absent, or below the limits of detection (~1 μM), in samples from P. aeruginosa-infected patients with little or no detectable
pyoverdine. Our data show that
pyoverdine is an important
iron-scavenging molecule for P. aeruginosa in many
cystic fibrosis patients, but other P. aeruginosa
iron-uptake systems must be active in some patients to satisfy the bacterial need for
iron.