Modulation of the Solid-Ordered/Liquid-Disordered Melting Temperature in Staphylococcus Aureus during Biofilm Formation

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. This points to a possible mechanism for generating resistance during biofilm formation through the modulation of lipid packing. Bacterial membranes present broad but cooperative lipid chain-melting events, where the membrane transitions from a solid-ordered (so) state, characterized by a high level of lipid packing, into a liquid-disordered (ld) state. For example, for Staphylococcus aureus (Sa) in planctonic state, this melting event occurs at 15°C. We have recently shown that, for Sa, the solid-ordered phase provides resistance towards PLA2-IIA. In this work we show, by measuring generalized polarization of Laurdan incorporated into lipid extracts, that the position of this melting event is shifted to 28°C during Sa biofilm formation. Additionally, we present evidence that this shift in the melting temperature modulates resistance towards PLA2-IIA and magainin-2. These results point to a mechanism by which bacterial membranes can generate resistance towards membrane active antibacterial agents through the modulation of the so/ld chain melting event during biofilm formation.