Pseudomonas aeruginosa microevolution during cystic fibrosis lung infection establishes clones with adapted virulence.
BACKGROUND
During long-term lung infection in patients with cystic fibrosis (CF), Pseudomonas aeruginosa strains develop mutations leading to clonal expansion. This microevolution is believed to be correlated with a reduced virulence.


OBJECTIVE
We tested this hypothesis in models of lung infection, using mice with different genetic backgrounds.


METHODS
From infected airways of six patients with CF, 25 P. aeruginosa clones were isolated during a period of up to 16.3 years and genotypically and phenotypically characterized. Virulence of the 8 early, 6 intermediate, and 11 late CF isolates and 5 environmental strains was assessed by monitoring acute mortality versus survival and P. aeruginosa chronic persistence versus lung clearance in mice of different genetic backgrounds, including CF mice.


RESULTS
Different patients harbored clonally unrelated strains, but early, intermediate, and late P. aeruginosa isolates from single patients were clonally related, allowing comparative in vivo analysis. Although late isolates were attenuated in causing acute mortality in the mouse models, compared with early and intermediate clonal isolates and environmental strains, they did not differ from early and intermediate clonal isolates in their capacity to establish chronic infection and cause extensive inflammation in the murine respiratory tract.


CONCLUSIONS
Our findings indicate that clonal expansion of P. aeruginosa strains during microevolution within CF lungs leads to populations with altered but not reduced virulence. These P. aeruginosa clones with adapted virulence play a critical role in the pathogenesis of chronic infections and may serve to define virulence determinants as targets for novel therapies.
Infections and Cystic Fibrosis Unit, Division of Immunology, Transplantation and Infectious Diseases, San Raffaele Scientific Institute, Milano, Italy. bragonzi.alessandra@hsr.it
Alessandra
A
Bragonzi
Moira
M
Paroni
Alessandro
A
Nonis
Nina
N
Cramer
Sara
S
Montanari
Joanna
J
Rejman
Clelia
C
Di Serio
Gerd
G
Döring
Burkhard
B
Tümmler
D000818:Animals; D002908:Chronic Disease; D002999:Clone Cells / Q000502:physiology; D003550:Cystic Fibrosis / Q000382:microbiology* / Q000473:pathology; D004195:Disease Models, Animal; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018181:Mice, Inbred CFTR; D011552:Pseudomonas Infections / Q000382:microbiology* / Q000473:pathology*; D011550:Pseudomonas aeruginosa / Q000302:isolation & purification / Q000472:pathogenicity*; D012141:Respiratory Tract Infections / Q000382:microbiology* / Q000473:pathology*; D014774:Virulence