Lipid A-dependent morphology and its effect on antimicrobial resistance of ESKAPE Gram-(-) bacteria

1 p.AntiMicrobial Resistance (AMR) has dramatically increased over the past three decades becoming a worldwide health emergency.Strains of particular concern are known by the acronym ESKAPE, which groups Gram-(+) bacteria: Enterococcus faecium, Staphylococcus aureus; and, Gram-(-) bacterias: Klebsiella pneumoniae (K.p.), Acinetobacter baumannii (A.b.),Pseudomonas aeruginosa (P.a.), and Enterobacter species (e.g., Escherichia coli, E.c.). In particular, Gram-(-) bacteria are highlighted due to their cell envelope complexity which exhibits strong resistance to antimicrobials. Their cell wall contains the periplasm membrane and a thin peptidoglycan layer encased by the outer membrane (OM). The OM acts as protective and selective barrier to most small drugs. Its mechanisms of resistance involve chemical alterations of lipopolysaccharides (LPS), which face the external environment and are indispensable for the bacterial survival.The LPS structure is composed by three main chemical units: a lipid A, a core oligosaccharide and an O-antigen. A key element for AMR is the chemical structure of the lipid A moiety whose changes (e.g., acyl chain length, saturation, branching, and charged head groups) induce physico-chemical property modifications such as fluidity, charge balance, and permeability to antibiotics.3 Liposomes are used as biological membrane models which by tuning their lipid composition can mimic membrane vesicles of pathogenic bacteria, and thus,help to understand AMR mechanisms and to promote drug discovery. Nevertheless, although great progress has been made on the development of computational membrane models to understand resistance mechanisms at molecular level, computational studies with liposomes are scarce.In this work, coarse-grained (CG) molecular dynamics (MD) simulations were used to model liposomes from ESKAPE Gram-(-) bacteria (K.p., A.b., P.a., E.c.). We captured the role of lipid A and cholesterol on liposome morphology and physico-chemical properties. Additionally,three antimicrobial peptides (AMPs) were used to unveil their implications on membrane disruption and their effect on the physico-chemical properties of bacterial liposomes. This novel study opens promising avenues to understand the hidden molecular keys of bacterial membranes and to develop new AMPs to overcome AMR.Peer reviewe