The occurrence of nosocomial infections has been on the rise for the past twenty years. Notably, infections caused by the Gram-positive bacteria Staphylococcus aureus represent a major clinical problem, as an increase in antibiotic multi-resistant strains has accompanied this rise. There is thus a crucial need to find and characterize new antibiotics against Gram-positive bacteria, and against antibiotic-resistant strains in general. We identified a new dermaseptin, DMS-DA6, produced by the skin of the Mexican frog Pachymedusa dacnicolor, with specific antibacterial activity against Gram-positive bacteria. This peptide is particularly effective against two multiple drug-resistant strains Enterococcus faecium BM4147 and Staphylococcus aureus DAR5829, and has no hemolytic activity. DMS-DA6 is naturally produced with the C-terminal carboxyl group in either the free or amide forms. By using Gram-positive model membranes and different experimental approaches, we showed that both forms of the peptide adopt an α-helical fold and have the same ability to insert into, and to disorganize a membrane composed of anionic lipids. However, the bactericidal capacity of DMS-DA6-NH2 was consistently more potent than that of DMS-DA6-OH. Remarkably, rather than resulting from the interaction with the negatively charged lipids of the membrane, or from a more stable conformation towards proteolysis, the increased capacity to permeabilize the membrane of Gram-positive bacteria of the carboxyamidated form of DMS-DA6 was found to result from its enhanced ability to interact with peptidoglycan.
Mycobacterium tuberculosis is the causal agent of tuberculosis. Tumor necrosis factor alpha (TNF-␣), transforming growth factor  (TGF-), and gamma interferon (IFN-␥) secreted by activated macrophages and lymphocytes are considered essential to contain Mycobacterium tuberculosis infection. The CD43 sialomucin has been reported to act as a receptor for bacilli through its interaction with the chaperonin Cpn60.2, facilitating mycobacterium-macrophage contact. We report here that Cpn60.2 induces both human THP-1 cells and mouse-derived bone marrow-derived macrophages (BMMs) to produce TNF-␣ and that this production is CD43 dependent. In addition, we present evidence that the signaling pathway leading to TNF-␣ production upon interaction with Cpn60.2 requires active Src family kinases, phospholipase C-␥ (PLC-␥), phosphatidylinositol 3-kinase (PI3K), p38, and Jun N-terminal protein kinase (JNK), both in BMMs and in THP-1 cells. Our data highlight the role of CD43 and Cpn60.2 in TNF-␣ production and underscore an important role for CD43 in the host-mycobacterium interaction.
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