title: LL-37 Triggers Formation of Streptococcus pyogenes Extracellular Vesicle-Like Structures with Immune Stimulatory Properties.
abstract: Reports have shown that the antimicrobial peptide LL-37 is abundantly expressed but has limited bactericidal effect in Streptococcus pyogenes infections. At sub-inhibitory concentrations, LL-37 has been reported to alter virulence gene expression. Here, we explored the interaction of S. pyogenes strains with LL-37, focusing on bacterial growth, cell surface alterations and pro-inflammatory responses. Bioscreen turbidity measurements of strain 5448 cultured in the presence or absence of LL-37 confirmed the poor antimicrobial effect, and revealed a significant increase in turbidity of bacterial cultures exposed to sub-inhibitory concentrations of LL-37. However, this was not linked to increased bacterial counts. Electron microscopy of LL-37-exposed bacteria revealed the presence of vesicle-like structures on the bacterial surface. The vesicles stained positive for LL-37 and were released from the bacterial surface. Concentrated supernatants enriched in these structures had a broader protein content, including several virulence factors, compared to supernatants from untreated bacteria. The supernatants from LL-37-exposed bacteria were pro-inflammatory and elicited resistin and myeloperoxidase release from neutrophils. This is the first report on S. pyogenes extracellular vesicle-like structures formed at the bacterial surface in response to LL-37. The associated increased pro-inflammatory activity further implicates LL-37 as a potential factor involved in S. pyogenes pathogenesis.
authors.affiliation: Center for Infectious Medicine, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Julia
authors.initials: J
authors.lastname: Uhlmann
authors.forename: Manfred
authors.initials: M
authors.lastname: Rohde
authors.forename: Nikolai
authors.initials: N
authors.lastname: Siemens
authors.forename: Bernd
authors.initials: B
authors.lastname: Kreikemeyer
authors.forename: Peter
authors.initials: P
authors.lastname: Bergman
authors.forename: Linda
authors.initials: L
authors.lastname: Johansson
authors.forename: Anna
authors.initials: A
authors.lastname: Norrby-Teglund
mesh_terms: D023181:Antimicrobial Cationic Peptides / Q000378:metabolism*; D048708:Cell Growth Processes; D000067128:Extracellular Vesicles / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D007114:Immunization; D018836:Inflammation Mediators / Q000378:metabolism*; D018375:Neutrophil Activation; D009504:Neutrophils / Q000276:immunology; D009195:Peroxidase / Q000378:metabolism; D052243:Resistin / Q000378:metabolism; D013290:Streptococcal Infections / Q000276:immunology*; D013297:Streptococcus pyogenes / Q000502:physiology* / Q000648:ultrastructure; D054804:Cathelicidins
chemical_list: D023181:Antimicrobial Cationic Peptides; D018836:Inflammation Mediators; D052243:Resistin; D009195:Peroxidase; D054804:Cathelicidins