L-Rhamnosylation of Listeria monocytogenes Wall Teichoic Acids Promotes Resistance to Antimicrobial Peptides by Delaying Interaction with the Membrane

Listeria monocytogenes is an opportunistic gram-positive bacterial pathogen responsible for listeriosis,a human foodborne disease. its cell wall is densely decorated with wall teichoic acids (wtas),a class of anionic glycopolymers that play key roles in bacterial physiology,including protection against the activity of antimicrobial peptides (amps). in other gram-positive pathogens,wta modification by amine-containing groups such as d-alanine was largely correlated with resistance to amps. however,in l. monocytogenes,where wta modification is achieved solely via glycosylation,wta-associated mechanisms of amp resistance were unknown. here,we show that the l-rhamnosylation of l. monocytogenes wtas relies not only on the rmlacbd locus,which encodes the biosynthetic pathway for l-rhamnose,but also on rmlt encoding a putative rhamnosyltransferase. we demonstrate that this wta tailoring mechanism promotes resistance to amps,unveiling a novel link between wta glycosylation and bacterial resistance to host defense peptides. using in vitro binding assays,fluorescence-based techniques and electron microscopy,we show that the presence of l-rhamnosylated wtas at the surface of l. monocytogenes delays the crossing of the cell wall by amps and postpones their contact with the listerial membrane. we propose that wta l-rhamnosylation promotes l. monocytogenes survival by decreasing the cell wall permeability to amps,thus hindering their access and detrimental interaction with the plasma membrane. strikingly,we reveal a key contribution of wta l-rhamnosylation for l. monocytogenes virulence in a mouse model of infection. © 2015 carvalho et al.