Persistent cystic fibrosis isolate Pseudomonas aeruginosa strain RP73 exhibits an under-acylated LPS structure responsible of its low inflammatory activity

•Elucidation of the cystic fibrosis chronic strain P. aeruginosa RP73 LOS structure.•Analyses show a core oligosaccharide typically present in P. aeruginosa strains.•P. aeruginosa RP73 lipid A is different from previously elucidated lipid A forms.•P. aeruginosa RP73 LOS has a low inflammatory capacity.•We propose that LPS lipid A under-acylation is a hallmark of chronic infections.

Pseudomonas aeruginosa, the major pathogen involved in lethal infections in cystic fibrosis (CF) population, is able to cause permanent chronic infections that can persist over the years. This ability to chronic colonize CF airways is related to a series of adaptive bacterial changes involving the immunostimulant lipopolysaccharide (LPS) molecule. The structure of LPSs isolated from several P. aeruginosa strains showed conserved features that can undergo chemical changes during the establishment of the chronic infection. In the present paper, we report the elucidation of the structure and the biological activity of the R-LPS (lipooligosaccharide, LOS) isolated from the persistent CF isolate P. aeruginosa strain RP73, in order to give further insights in the adaptation mechanism of the pathogen in the CF environment. The complete structural analysis of P. aeruginosa RP73 LOS was achieved by chemical analyses, NMR spectroscopy and MALDI MS spectrometry, while the assessment of the biological activity was attained testing the in vivo pro-inflammatory capacity of the isolated LOS molecule. While a typical CF LPS is able to trigger a high immune response and production of pro-inflammatory molecules, this P. aeruginosa RP73 LOS showed to possess a low pro-inflammatory capacity. This was possible due to a singular chemical structure possessing an under-acylated lipid A very similar to the LPS of P. aeruginosa found in chronic lung diseases such as bronchiectstasis.

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