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

• Main Authors: Filipe Carvalho, Magda L Atilano, Rita Pombinho, Gonçalo Covas, Richard L Gallo, Sérgio R Filipe, Sandra Sousa, Didier Cabanes
• Format: Article
• Language: English
• Published: Public Library of Science (PLoS) 2015-05-01
• Series: PLoS Pathogens
• Online Access: http://europepmc.org/articles/PMC4441387?pdf=render

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.