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- Musa, Amani, 1983-
(författare)
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Plantaricins as a novel group of antibacterial compounds and enhancers of antibiotics
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Antibiotics have revolutionized medicine, however, the rapid development of an-tibiotic resistance among bacteria is diminishing their efficacy. Antimicrobial pep-tides produced by Lactobacillus plantarum, i.e., plantaricins, are considered prom-ising alternatives to antibiotics against infections. In this thesis, the antimicrobial activities of different plantaricins (Pln A, Pln EF, Pln JK, and PLNC8 αβ) were investigated against antibiotic-resistant and susceptible strains of Staphylococcus spp, biofilm-forming strains, as well as clinical isolates of ESKAPE pathogens, and Escherichia coli. Moreover, the stability, cytotoxicity, and immunomodulatory effects of PLNC8 αβ were characterized. The results show that Pln EF and Pln JK have potent antimicrobial activity against Staphylococcus epidermidis and effectively enhance the effects of various antibiotics. Furthermore, PLNC8 αβ shows potent antibacterial effects against different Gram-positive and Gram-negative bacteria, including vancomycin- and methicillin-resistant strains. The antibacterial effects and stability following peptide truncation and D-amino acid substitution were investigated. D-amino acid substitution did not change the antimicrobial activity of PLNC8 αβ, however, it increased the stability of the peptide as it was more resistant to proteolysis by trypsin compared to the native L-enantiomer. Moreover, among the truncated peptides, α1–22, β7–34, and β1–20 retained bacteriostatic effects without displaying bactericidal activity. L-PLNC8 αβ peptides were tested for their antibiofilm properties and displayed rapid disruption of surface-associated S. epidermidis. Electron microscopy shows that PLNC8 αβ targets bacterial cell membranes, ultimately resulting in rapid permeabilization and altered homeostasis, including ATP release. PLNC8 αβ does not show any cytotoxic or hemolytic effects on human cells in vitro. Furthermore, PLNC8 αβ counteracted the cytotoxic effects and expression of inflammatory mediators that were induced by S. aureus, including MMPs and growth factors that are essential in cell regeneration. Pathogen recognition receptors (TLR2, TLR4, and PAR2), intracellular signaling events (c-Jun, c-Fos), and inflammatory mediators (IL-1β, IL-6, CXCL-8), that facilitate pathogen recognition, cell survival, and cellular communication, were all enhanced by the peptides. At sub-MIC concentrations, PLNC8 αβ enhanced the activity of various antibiotics against both Gram-positive and Gram-negative ESKAPE bacteria. In conclusion, plantaricins efficiently impede bacterial pathogens and enhance the activity of antibiotics and thereby constitute a therapeutic option to counter the threatening situation with severe antibiotic-resistant infections.
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| 2. |
- Wassing, Gabriela, 1989-
(författare)
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Bacteria-host cell interactions : Studies on initial colonization, antimicrobial peptides, and biofilms
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The obligate human pathogen Neisseria meningitidis asymptomatically colonizes the upper respiratory tract, but crossing of the epithelial barrier can cause life-threatening meningitis and/or sepsis. N. meningitidis encounters numerous environmental challenges during colonization in the host, and has evolved different evasion strategies and virulence factors to ensure its survival. In contrast, Lactobacillus species are part of the human microbiota and their commensal colonization confers many benefits to the host, including the inhibition of pathogens.The first cell type encountered by invading bacteria are epithelial cells and immune cells, which can effectively sense and respond to the presence of bacteria by alerting the immune system or by release of antimicrobial peptides. Antimicrobial peptides are small peptides that are able to directly kill bacteria, but also play a role in modulation of immune responses. This thesis focuses on the interaction between the human host and bacteria. Paper I shows that epithelial colonization by different bacterial species induces the transcription factor early growth response protein 1 (EGR1). Induction of EGR1 is mediated primarily by signaling through EGFR and ERK1/2 pathway. In paper II the ability of N. meningitidis and Lactobacillus to modulate expression of antimicrobial peptide human beta-defensin 2 (hBD2) in epithelial cells is compared. Expression of hBD2 is upregulated by lactobacilli. In contrast, N. meningitidis dampens this effect, likely mediated by induction of the host molecule A20, a negative regulator of NF-κB. Since N. meningitidis is susceptible to hBD2-mediated killing, exploitation of A20 may be an immune evasion mechanism. In paper III we demonstrate that hBD2 is able to kill N. meningitidis without causing membrane permeabilization. N. meningitidis DNA can bind hBD2 and thereby inhibit hBD2-mediated killing, presenting a possible evasion mechanism. Finally, paper IV shows that the absence of D-lactate dehydrogenase LdhA in N. meningitidis promotes aggregation and biofilm formation through increased autolysis-mediated release of extracellular DNA.
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