Background: Pseudomonas aeruginosa is a bacterium able to induce serious pulmonary infections in cystic fibrosis (CF) patients. This bacterium is very often antibiotic resistant, partly because of its membrane impermeability, which is linked to the membrane lipid composition. This work aims to study the membrane phospholipids of P. aeruginosa grown in CF sputum-like media.
Methods: Three media were used: Mueller Hilton broth (MHB), synthetic cystic fibrosis medium (SCFM) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) complemented SCFM (SCFM-PC). Lipids were extracted and LC-MS/MS analyses were performed. Growth curves, atomic force microscopy images and minimal inhibitory concentration determination were performed in order to compare the growth and potentially link lipid modifications to antibiotic resistance.
Results: Semi-quantification showed phospholipid quantity variation depending on the growth medium. Phosphatidylcholines were detected in traces in SCFM. MS/MS experiments showed an increase of phospholipids derived from DOPC in SCFM-PC. We observed no influence of the medium on the bacterial growth and a minor influence on the bacterial shape. MIC values were generally higher in SCFM and SCFM-PC than in MHB.
Conclusions: We defined a CF sputum-like media which can be used for the membrane lipid extraction of P. aeruginosa. We also showed that the growth medium does have an influence on its membrane lipid composition and antibiotic resistance, especially for SCFM-PC in which P. aeruginosa uses DOPC, in order to make its own membrane.
General significance: Our results show that considerable caution must be taken when choosing a medium for lipid identification and antibiotic testing -especially for phospholipids-enriched media.
Keywords: Antibiotic resistance; CF sputum; Culture medium; Mass spectrometry; Membrane lipids; Pseudomonas aeruginosa.
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