Bacterial Biofilm Formation Induces Strong Shifts in Lipid Composition Resulting in Increased Resistance Towards Antimicrobial Peptide Activity

Abstract

Bacteria that interact with surfaces under hydrated conditions can form aggregated structures known as biofilms. Biofilms are characterized by having increased resistance to a variety of antibacterial agents. This resistance is responsible for the generation of persistent chronic infections, and represents a serious threat to human health. Several antimicrobial agents, including hydrolytic enzymes such as PLA2-IIA and antimicrobial peptides (AMPs) such as Magainin-2, act by disrupting bilayer membrane integrity. Since these antimicrobial agents require physical disruption of the bilayer membrane, their activity is likely to be sensitive to lipid packing.. In this work we show, by measuring generalized polarization of Laurdan incorporated into lipid extracts, drastic changes in the level of lipid packing in Staphylococcus aureus during biofilm formation. When analyzing lipid composition we find a significant reduction in the level of branched lipids in the biofilm membranes. A strong reduction in the level of carotenoids is also observed during biofilm formation. Additionally, we present evidence that this shift in the melting temperature modulates resistance towards magainin-2 at 37C where bacterial lipids are in the liquid-crystalline phase. These results point to a mechanism by which bacterial membranes can generate resistance towards membrane active antibacterial agents through the modulation of lipid composition during biofilm formation.