Melbourne Dental School - Research Publications
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ItemA Rapid and Quantitative Flow Cytometry Method for the Analysis of Membrane Disruptive Antimicrobial Activity(PUBLIC LIBRARY SCIENCE, 2016-03-17)We describe a microbial flow cytometry method that quantifies within 3 hours antimicrobial peptide (AMP) activity, termed Minimum Membrane Disruptive Concentration (MDC). Increasing peptide concentration positively correlates with the extent of bacterial membrane disruption and the calculated MDC is equivalent to its MBC. The activity of AMPs representing three different membranolytic modes of action could be determined for a range of Gram positive and negative bacteria, including the ESKAPE pathogens, E. coli and MRSA. By using the MDC50 concentration of the parent AMP, the method provides high-throughput, quantitative screening of AMP analogues. A unique feature of the MDC assay is that it directly measures peptide/bacteria interactions and lysed cell numbers rather than bacteria survival as with MIC and MBC assays. With the threat of multi-drug resistant bacteria, this high-throughput MDC assay has the potential to aid in the development of novel antimicrobials that target bacteria with improved efficacy.
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ItemPorphyromonas gingivalis Lipopolysaccharide Weakly Activates M1 and M2 Polarized Mouse Macrophages but Induces Inflammatory Cytokines(AMER SOC MICROBIOLOGY, 2014-10)Porphyromonas gingivalis is associated with chronic periodontitis, an inflammatory disease of the tooth's supporting tissues. Macrophages are important in chronic inflammatory conditions, infiltrating tissue and becoming polarized to an M1 or M2 phenotype. As responses to stimuli differ between these phenotypes, we investigated the effect of P. gingivalis lipopolysaccharide (LPS) on M1 and M2 macrophages. M1 and M2 polarized macrophages were produced from murine bone marrow macrophages (BMMϕ) primed with gamma interferon (IFN-γ) or interleukin-4 (IL-4), respectively, and incubated with a low or high dose of P. gingivalis LPS or control TLR2 and TLR4 ligands. In M1-Mϕ, the high dose of P. gingivalis LPS (10 μg/ml) significantly increased the expression of CD40, CD86, inducible nitric oxide synthase, and nitric oxide secretion. The low dose of P. gingivalis LPS (10 ng/ml) did not induce costimulatory or antibacterial molecules but did increase the secretion of IL-1α, IL-6, IL-12p40, IL-12p70, and tumor necrosis factor alpha (TNF-α). P. gingivalis LPS marginally increased the expression of CD206 and YM-1, but it did enhance arginase expression by M2-Mϕ. Furthermore, the secretion of the chemokines KC, RANTES, eotaxin, and MCP-1 from M1, M2, and nonpolarized Mϕ was enhanced by P. gingivalis LPS. TLR2/4 knockout macrophages combined with the TLR activation assays indicated that TLR2 is the main activating receptor for P. gingivalis LPS and whole cells. In conclusion, although P. gingivalis LPS weakly activated M1-Mϕ or M2-Mϕ compared to control TLR ligands, it induced the secretion of inflammatory cytokines, particularly TNF-α from M1-Mϕ and IL-10 from M2-Mϕ, as well as chemotactic chemokines from polarized macrophages.
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ItemMaculatin 1.1 Disrupts Staphylococcus aureus Lipid Membranes via a Pore Mechanism(AMER SOC MICROBIOLOGY, 2013-08)Maculatin 1.1 (Mac1) showed potent activity against Staphylococcus aureus with an MIC of 7 μM. The mode of action of Mac1 was investigated by combining assays with S. aureus cells and lipid vesicles mimicking their membrane composition. A change in Mac1 conformation was monitored by circular dichroism from random coil to ca. 70% α-helix structure in contact with vesicles. Electron micrographs of S. aureus incubated with Mac1 showed rough and rippled cell surfaces. An uptake of 65% of small (FD, 4 kDa [FD-4]) and 35% of large (RD, 40 kDa [RD-40]) fluorescent dextrans by S. aureus was observed by flow cytometry and indicate that Mac1 formed a pore of finite size. In model membranes with both dyes encapsulated together, the full release of FD-4 occurred, but only 40% of RD-40 was reached, supporting the flow cytometry results, and indicating a pore size between 1.4 and 4.5 nm. Finally, solid-state nuclear magnetic resonance showed formation of an isotropic phase signifying highly mobile lipids such as encountered in a toroidal pore structure. Overall, Mac1 is a promising antimicrobial peptide with the potent capacity to form pores in S. aureus membranes.
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ItemNo Preview AvailablePolymerisation of a T Cell Epitope with an Immunostimulatory C3d Peptide Sequence Enhances Antigen Specific T Cell Responses(SPRINGER, 2013-03)The complement protein C3d and C3d derived peptides that bind CD21 are known to enhance immunity to co-immunised antigens. In this study we have synthesised the minimal CD21 binding sequence of C3d (1227LYNVEA 1232) as mono, di and tri tandem repeats and derivatised the N-terminus with an acryloyl moiety. These acryloyl-(C3d)n peptides were co-polymerised with a acryloyl-T cell epitope (PAS1K) from the Porphyromonas gingivalis antigen the RgpA–Kgp proteinase–adhesin complex. The ability of C3d containing polymers to enhance T cell immunity in vitro and in vivo was evaluated. When used to stimulate in vitro PAS1K-primed or RgpA–Kgp complex-primed T cells the C3d containing PAS1K polymers induced a mixed and significantly (p\0.05) higher IL-4 and IFNc T cell response compared to that induced by the PAS1K peptide or polymer. PAS1K polymers containing tandem repeats of C3d induced a significantly (p\0.05) stronger maximal proliferative response, at the same antigenic dose, compared to that induced by the PAS1K peptide or polymer. When used as immunogens to prime T cells all of the C3d containing PAS1K polymers induced a dominant IFNc T cell response and reduced the antigen dose required for maximal proliferation 150-fold compared to that required for the PAS1K-peptide or polymer primed T cells. In conclusion, the 6 residue sequence LYNVEA from C3d is sufficient to enhance immunity to an antigen and that the effect is more pronounced when C3d is part of the immunising antigen rather than an in vitro stimulating antigen.