An investigation of the mycotoxins produced by a toxic strain of Fusarium graminearum Schwabe

Thesis (M. Sc.) -- University of Stellenbosch, 1987.Full text to be digitised and attached to bibliographic record

Polar

Introduction. Penicillium digitatum is a commercially important postharvest pathogen of citrus that is responsible for significant annual global losses. Strains of the fungus, which exhibit strong resistance to widely used synthetic fungicides, are of major concern to the industry. The aim of the study was to investigate the antifungal activities of polar extracts and compounds from Lippia species, indigenous to South Africa, against a Guazatine®-resistant strain of P. digitatum. Materials and methods. In vitro tests were done by incorporating the compounds and plant extracts into Malt Extract Agar at concentrations ranging from (0.2 to 1.0) mg·mL–1. An in vivo (curative) assay was conducted using the checkerboard technique on ‘Valencia’ oranges. Results and discussion. A strong correlation between the in vitro and in vivo results was observed. All the compounds and extracts were able to inhibit fungal growth at concentrations above 0.6 mg·mL–1. Verbascoside was the most active compound, while extracts of Lippia javanica and Lippia rehmannii caused significant inhibition of mycelial growth. The observed activity was largely ascribed to the presence of verbascoside in the plant extracts. Conclusion. Polar extracts of Lippia species have potential as environmentally friendly alternatives for the control of P. digitatum on citrus

Temporal and spatial variations of organochlorine pesticides (OCPs) and phthalates affecting the quality of water and sediment from Loskop Dam, South Africa

Organochlorine pesticides (OCPs) and phthalates are amongst the most emphasized man-made environmental contaminants, due to their prevalence, persistence and potential to induce adverse effects in organisms. In addition to prevailing industrial and domestic activities, their presence in the environment is exacerbated by leaching from associated materials, run-off and emissions. The Loskop Dam in the Mpumalanga Province, South Africa, is located on the Olifants River, which flows through a hub of industrial and agricultural activities. Research aimed at monitoring the levels of OCPs and phthalate contamination in South Africa, particularly in the Olifants catchment, has been limited and is restricted to short-term monitoring. In this study, the spatial and temporal variations of 21 OCPs and 7 phthalates in water and sediments from Loskop Dam were evaluated over a 3-year period (2015–2017). Annual average OCP levels ranged from 0.013±0.006 to 0.36±0.13 μg/L in water and from below the limit of detection to 2.4±1.2 µg/kg in sediments. Phthalates were present at average concentrations ranging from 0.023±0.041 to 2.1±1.5 μg/L and 20±0.63 to 55±6.9 µg/kg in water and sediments, respectively. The levels of OCPs and phthalates were greatest in autumn, attributed to higher input sources and concentration effects due to lower water levels. Phthalates were present at greater quantities at the inlet, while OCP accumulation was observed at the upper reaches of the dam. This may be an indication of the differences in input sources and translocation of these compounds, related to the topography of the dam and variability in water flow rates. These findings are important in highlighting the environmental and health concerns that may arise in the Olifants catchment area. After considering the outcomes of this study, we propose the implementation of regular and stringent monitoring strategies, which include surveys of OCPs and phthalates for Loskop Dam and similar water systems globally

Myricetin: A Dietary Molecule with Diverse Biological Activities

Myricetin is a common plant-derived flavonoid and is well recognised for its nutraceuticals value. It is one of the key ingredients of various foods and beverages. The compound exhibits a wide range of activities that include strong anti-oxidant, anticancer, antidiabetic and anti-inflammatory activities. It displays several activities that are related to the central nervous system and numerous studies have suggested that the compound may be beneficial to protect against diseases such as Parkinson’s and Alzheimer’s. The use of myricetin as a preserving agent to extend the shelf life of foods containing oils and fats is attributed to the compound’s ability to protect lipids against oxidation. A detailed search of existing literature revealed that there is currently no comprehensive review available on this important molecule. Hence, the present work includes the history, synthesis, pharmaceutical applications and toxicity studies of myricetin. This report also highlights structure-activity relationships and mechanisms of action for various biological activities

Exploring Common Culinary Herbs and Spices as Potential Anti-Quorum Sensing Agents

Quorum sensing controls bacterial pathogenesis and virulence; hence, interrupting this system renders pathogenic bacteria non-virulent, and presents a novel treatment for various bacterial infections. In the search for novel anti-quorum sensing (AQS) compounds, 14 common culinary herbs and spices were screened for potential antipathogenicity activity against Chromobacterium violaceum ATCC 12472. Extracts of Glycyrrhiza glabra (liquorice), Apium graveolens (celery), Capsicum annuum (cayenne pepper) and Syzygium anisatum (aniseed) demonstrated good AQS potential, yielding opaque halo zones ranging from 12–19 mm diameter at sub-minimum inhibitory concentrations (0.350–4.00 mg/mL). For the same species, the percentage reduction in violacein production ranged from 56.4 to 97.3%. Zones with violacein inhibitory effects were evident in a celery extract analysed using high performance thin layer chromatography-bio-autography. The major active compound was isolated from celery using preparative-high performance liquid chromatography-mass spectrometry and identified using gas chromatography-mass spectrometry (GC-MS) as 3-n-butyl-4,5-dihydrophthalide (sedanenolide). Potent opaque zones of inhibition observed on the HPTLC-bio-autography plate seeded with C. violaceum confirmed that sedanenolide was probably largely responsible for the AQS activity of celery. The bacteriocidal properties of many herbs and spices are reported. This study, however, was focussed on AQS activity, and may serve as initial scientific validation for the anti-infective properties ascribed to several culinary herbs and spices

Development of EVA and LLDPE polymer-based carvone and spearmint essential oil release systems for citrus postharvest diseases applications

Carvone and spearmint essential oil vapours are suitable candidates for the control of citrus postharvest pathogens due to their strong antifungal activity. However, the high volatility of essential oils remains a hurdle that needs to be overcome before it can be applied as an alternative fungicide. This work investigates the antifungal activity of 20 and 30 wt-% spearmint essential oil or carvone, incorporated into ethylene–vinyl acetate (EVA) and linear low-density polyethylene (LLDPE) strands postharvest pathogens affecting kumquats. Following the melt-extrusion process, an average yield of 16–29 % and 15–28 % of the total carvone and spearmint essential oil, respectively, was determined in the polymer strands. Morphological studies using scanning electron microscopy (SEM) revealed the presence of microporous structures in the internal structure of the strands. The membrane-like skin that covers the polymer strand was also confirmed by SEM. Variations in the release rates were observed between carvone and spearmint essential oils, which was attributed to the difference in the vapour pressure of the neat essential oils. Furthermore, in this study, the results demonstrated that the diffusion exponent ‘n’ of the Korsmeyer–Peppas, Weibull and Log-logistic models exceeded 1.0. In most cases, the Super Case II mechanism was observed. In the case of the Mapossa model, as k2 was ˃> 1, it implies that the outer skin-like membrane covering the polymer strand fully controlled the carvone release. The application of the essential oil-loaded polymer strands resulted in a significant reduction in deterioration, caused by citrus postharvest pathogens, of kumquats kept at room temperature for 21 days. This study indicates that the incorporation of spearmint essential oil or carvone into LLDPE or EVA polymer strands promoted the preservation of kumquat over a 21-day period

Anti-quorum sensing and antimicrobial activities of South African medicinal plants against uropathogens

Urinary tract infections (UTIs) primarily affect women and have increasingly become a serious health problem globally. These infections are largely attributed to the quorum sensing (QS)-dependent ability of pathogens to form biofilms in the urinary tract. Microbial pathogenicity can be attenuated by disturbing the QS system of bacteria. The aim of the study was to document the antibacterial and anti-quorum sensing (AQS) potential of medicinal plants that are used as traditional medicine in South Africa to treat UTIs. Of the 70 plant extracts prepared from 14 medicinal plants using solvents of different polarities, only 6 displayed noteworthy activity (MIC < 1 mg/mL) against Pseudomonas aeruginosa, Staphylococcus aureus, Serratia marcescens, Escherichia coli and Proteus mirabilis. Extracts of Hydnora africana, Hypoxis hemerocallidea and Prunus africana displayed good antibacterial activity with MIC value of 0.5 mg/mL against S. aureus, but the methanol extracts of Rhoicissus tridentata and Cryptocarya latifolia were highly active against S. marcescens with MICs of 0.13 and 0.25 mg/mL, respectively. When plant extracts were screened for their ability to inhibit the QS-controlled violacein production by Chromobacterium violaceum, only two species (H. africana and C. latifolia) exhibited AQS activity in the qualitative agar well diffusion assay. However, eight extracts inhibited violacein production by 57–71% in the quantitative dilution assay. The ability of uropathogens to form biofilms upon exposure to the plant extracts was subsequently investigated using the crystal violet assay. It was found that the polar extracts of Cenchrus ciliaris and Eucomis autumnalis, Ranunculus multifidus, Vernonia adoensis, Cryptocarya latifolia, Hydnora africana, Rhoicissus tridentata and Hypoxis hemerocallidea, as well as non-polar extracts of Prunus africana and Hypoxis hemerocallidea were able to reduce initial cell attachment of S. aureus, P. mirabilis and S. marcescens by approximately 50%. However, the preformed biofilm was inhibited less than 30% by the extracts. The study revealed that several South African medicinal plants have antibacterial and AQS properties, validating their use in traditional medicines to treat UTIs to some degree, and indicating that they may be a suitable source of anti-pathogenic drugs to treat urinary infections.The National Research Foundation, the Department of Science and Technology of South Africa (through the SARChI initiative) as well as the South African Medical Research Council.http://www.elsevier.com/locate/sajb2020-05-01hj2019BiochemistryGeneticsMicrobiology and Plant Patholog