Uhlmann J, Rohde M, Siemens N, Kreikemeyer B, Bergman P, Johansson L, Norrby-Teglund A. LL-37 Triggers Formation of Streptococcus pyogenes Extracellular Vesicle-Like Structures with Immune Stimulatory Properties.
J Innate Immun 2015;
8:243-57. [PMID:
26641861 DOI:
10.1159/000441896]
[Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2015] [Accepted: 10/21/2015] [Indexed: 01/09/2023] Open
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.
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