Doctoral Degrees (Microbiology)
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Browsing Doctoral Degrees (Microbiology) by Subject "Antimicrobial peptides"
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- ItemDevelopment of an antimicrobial wound dressing by co-electrospinning bacteriocins of lactic acid bacteria into polymeric nanofibers(Stellenbosch : Stellenbosch University, 2012-12) Heunis, Tiaan de Jager; Dicks, Leon Milner Theodore; Stellenbosch University. Faculty of Science. Dept. of Microbiology.ENGLISH ABSTRACT: Skin is the largest organ in the human body and serves as a barrier that protects the underlying tissue of the host from infection. Injury, however, destroys this protective barrier and provides a perfect opportunity for microorganisms to invade the host and cause infection, thereby affecting the normal wound healing processes. Furthermore, the ability of microbial pathogens to rapidly develop resistance towards a variety of antimicrobial compounds hampers the effective treatment and control of infections. Antimicrobial-resistant pathogens are increasingly being isolated from patients, placing a huge burden on the health care sector. The search for new and novel antimicrobial agents and treatments is thus of utmost importance and will continue to play an integral role in medical research. Antimicrobial peptides (AMPs) may serve as possible alternatives to antibiotics, or may be used in combination with antibiotics to reduce the risk of antimicrobial resistance. AMPs play a role in innate defence and are produced by a variety of mammals, plants, reptiles, amphibians, birds, fish and insects. The AMPs of bacteria (bacteriocins), especially those of lactic acid bacteria (LAB), are receiving increased attention as antimicrobial agents to treat bacterial infections. Electrospun nanofibers have characteristics that make them suitable as wound dressings, i.e. high oxygen permeability, variable pore size, high surface area to volume ratio and nanofibers are morphologically similar to the extracellular matrix. The ability to incorporate of a variety of biologically active compounds into nanofibers increases their potential as wound dressings. A novel approach would be to incorporate bacteriocins from LAB into nanofiber scaffolds to generate antimicrobial wound dressings. In this study, the feasibility of co-electrospinning bacteriocins from LAB into nanofibers was investigated. Plantaricin 423, produced by Lactobacillus plantarum 423, was successfully co-electrospun into poly(ethylene oxide) (PEO) nanofibers. Plantaricin 423 retained activity after the electrospinning process and continued to inhibit the growth of Lactobacillus sakei DSM 20017T and Enterococcus faecium HKLHS. Viable cells of L. plantarum 423 were also successfully co-electrospun into PEO nanofibers, albeit with a slight reduction in viability. A nanofiber drug delivery system was developed for plantaricin 423 and bacteriocin ST4SA, produced by Enterococcus mundtii ST4SA, by blending PEO and poly(D,L-lactide) (PDLLA) in a suitable solvent before electrospinning. Nanofibers were produced that released the bacteriocins over an extended time period. The PEO:PDLLA (50:50) nanofiber scaffold retained its structure the best upon incubation at 37 °C and released active plantaricin 423 and bacteriocin ST4SA. Nisin A was also successfully co-electrospun into a PEO:PDLLA (50:50) nanofiber scaffold and nisin A, released from the nanofibers, inhibited the growth of Staphylococcus aureus in vitro. Nisin A-containing nanofiber scaffolds significantly reduced viable S. aureus cells in infected skin wounds and promoted wound healing in non-infected wounds. As far as we could determine we are the first to show that bacteriocin-eluting nanofiber scaffolds can be used to treat skin infections and influence wound healing.
- ItemProfiling of the secondary metabolites and the characterization two novel antilisterial peptides, xenopep and rhabdin, produced by xenorhabdus khoisanae(Stellenbosch : Stellenbosch University, 2022-04) Booysen, Elzaan; Dicks, Leon Milner Theodore; Rautenbach, Marina; Stellenbosch University. Faculty of Science. Dept. of Microbiology.ENGLISH ABSTRACT: In the early 1900’s the discovery of sulfonamides and penicillin paved the way for antibiotics and led to a boom in the discovery of other antibiotics. Unfortunately, this boom was short lived and soon the discovery and approval of novel antibiotics by the food and drug association and other similar associations dwindled. With the ever-increasing prevalence of antibiotic resistant pathogens this soon became a problem that was not foreseen. Most antibiotics currently on the market have been isolated from a select few genera. With nearly all the antibiotics from such few sources, bacteria were able to acquire resistance at an enhanced pace. This study focused on a relatively unexplored niche for novel antibiotics, from the genus Xenorhabdus. Species of this genus is mutually associated with Steinernema nematodes and have a unique life cycle. Xenorhabdus spp. are known to produce various secondary metabolites (SMs) that have antimicrobial, insecticidal, antiviral, immunosuppressant and proteolytic properties. Species from this genus use different synthesis machineries to produce these compounds, although the majority are produced via the non-ribosomal peptide synthesis. The ability of non-ribosomal peptides to incorporate non-proteogenic amino acids, D-amino acids, fatty chains, or polyketide chains result in unique resistance to proteinases and environmental stressors. Xenorhabdus khoisanae J194 is mutually associated with Steinernema jeffreyense J194, a nematode that was isolated from soil in the Eastern Cape. Culture conditions, especially oxygen, greatly affected SM production of X. khoisanae J194. PAX peptides, xenocoumacins and xenoamicins were identified in the cell-free crude extract of X. khoisanae J194 cultures. Two novel antilisterial peptides, xenopep and rhabdin, were also detected in the cell-free crude extract of. Xenopep has a narrow spectrum of activity and inhibited the growth of only, Listeria monocytogenes and Staphylococcus epidermidis, while rhabdin is active against both Gram-positive and Gram-negative bacteria. Xenopep and rhabdin share numerous characteristics and both contain a tetra-peptide in their structure including a tetra-peptide in their structure. Both peptides share the same amphipathic characteristic and behave similar suspension. Membrane potential and ATP release assays have shown that xenopep formed pores/lesions in the cell membrane of L. monocytogenes within minutes, followed by a rapid decrease in cell numbers over 3 hours. Scanning electron microscopy (SEM) images of L. monocytogenes treated with xenopep became elongated and formed filaments. This suggests that xenopep may inhibit penicillin binding protein three. This is the first study reporting on SMs produced by X. khoisanae when cultured under different conditions and is the first detailed description of antilisterial peptides produced by the species.