Influence of the Antimicrobial LL-37 Peptide on Legionella dumoffii Phospholipids Adsorbed at the Air–Liquid Interface

Legionella dumoffii is an intracellular pathogen of freshwater protozoans capable of infecting and multiplying in mammalian cells, causing a severe respiratory disease called Legionnaires’ disease. The pathomechanism of infection development is very complex and depends on many factors, including the structure and properties of macromolecules that build the components of the L. dumoffii cell envelope. Phospholipids (PLs) forming biological membranes have a significant impact on the integrity of the membrane as well as on the interactions with the host cells. L. dumoffii changes its lipid profile under the influence of external factors, which allows it to adapt to the living environment. One of the factors altering the PL composition is the presence of exogenous choline. The aim of this study was to determine the physicochemical properties of the model bacterial membranes adsorbed at the air–liquid interface (Langmuir monolayers). They were composed of phospholipids isolated from L. dumoffii cultured with (PL+choline) and without (PL−choline) choline. Moreover, the effect of the human cathelicidin (LL-37 peptide) added to the subphase on these monolayers was analyzed in terms of phospholipid–peptide interactions. The results indicated that the monolayers of PL+choline were slightly more condensed than PL−choline. In the presence of LL-37, the elasticity of both monolayers increased; thus, their molecular packing and ordering decreased. The disturbing effect was related to the peptide’s antibacterial activity.