Browsing by Author "Klaasen, J."

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    The effect of flavonoids on the in vitro activity of antibiotics against Staphylococcus aureus
    (University of the Western Cape, 2012) Ng’uni, Tiza Lucy; Fielding, Burtram C.; Klaasen, J.
    Staphylococcus aureus is a Gram-positive coccus belonging to the Stapylococcaeae family. S. aureus causes a wide range of infections that range from skin infections to lifethreatening infections such as pneumonia and endocarditis and is the major cause of hospital and community-acquired infections. Despite antibiotics being available for the treatment of S.aureus infections, resistance to a number of antibiotics has developed over the years due to their improper and continuous use. S. aureus develops resistance to various drugs via different mechanisms, one of which is the extrusion of the antibiotics through efflux pumps that play a role in its acquisition of multidrug resistance. The ability of methicillin-resistant S.aureus to develop resistance to a variety of antibiotics is causing global concern as treatment options are being limited. Various antimicrobial studies carried out on purified plant-based flavonoids have shown that flavonoids enhance the antibacterial effect of antibiotics. This study analysed antibacterial effects of the antibiotics; tetracycline, ampicillin, methicillin and vancomycin and three flavonoids; chrysin, naringenin and 7-hydroxyflavone, against methicillin-sensitive ATCC 25923 (MSSA) and methicillin-resistant ATCC 33591 (MRSA) S. aureus strains, using the Kirby-Bauer disk diffusion and microtitre microdilution assays. In the Kirby- Bauer assay, the antibiotics demonstrated inhibitory effects on the growth of MSSA ATCC 25923. However MRSA ATCC 33591 was only susceptible to vancomycin, with minimal inhibition zones observed with ampicillin. The flavonoids did not enhance or reduce the antibacterial activities of the antibiotics as the zones of inhibition sizes remained unchanged in the combination studies. Microtitre assay results revealed that naringenin enhanced the antibacterial activities of the antibiotics tetracycline and ampicillin, against MSSA ATCC 25923 and MRSA 33591. This was evident as calculated synergistic ratios by the Abbot formula showed that naringenin had an additive effect. The presence of the efflux pump genes in MSSA ATCC 25923 and MRSA ATCC 33591 was compared using polymerase chain reaction (PCR). The mepA and gyrA genes were identified in both strains whereas sepA was identified in MRSA ATCC 33591. The presence of efflux pump genes in both MSSA ATCC 25923 and MRSA ATCC 33591 also confirmed that the presence or absence of the genes may contribute to antibiotic resistance. The presence of sepA in the MRSA and not the MSSA confirmed that this gene plays a role in conferring drug resistance.
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    Synergistic effects of mixtures of the kresoxim-methyl fungicide and medicinal plant extracts in vitro and in vivo against Botrytis cinerea
    (University of the Western Cape, 2005) Knowles, Cindy-Lee; Klaasen, J.; Johnson, Q.
    The fungus Botrytis cinerea is an opportunistic pathogen on a wide variety of crops, causing a disease known as grey mould through infections via wounds or dead plant parts. Synthetic fungicides for controlling this disease are fast becoming ineffective due to the development of resistance. This, coupled with consumers' world wide becoming increasingly conscious of potential environmental and health problems associated with the build-up of toxic chemicals, (particularly in food products), have resulted in pressure to reduce the use of chemical pesticide volumes as well as its residues. An emerging alternative to random chemical synthesis is the study and exploitation of naturally occurring products with fungicidal properties. One group of compounds known as strobilurins produced by Strobilurus species, woodland basidiomycete fungi, is a good example of this phenomenon. Plants produce an enormous array of secondary metabolites, and it is commonly reasoned that a significant part of this chemical diversity serves to protect plants against plant pathogens. A problem with plant-produced compounds as potential fungicides is that in the natural state, they are generally only weakly active compared to synthetic fungicides. There have been reports on the uses of mixtures of synthetic fungicides for the control of plant pathogenic fungi. When utilized in two-way mixtures, such fungicides may maintain or enhance the level of control of a pathogen at reduced rates for both components utilized in combinations, or alone at normal rates. These studies provide an important precedent for the idea of synergism. For this study, we hypothesize that the addition of plant extracts may enhance the antifungal efficacy of the synthetic strobilurin fungicide, kresoxim-rnethyl against B. cinerea. We selected South African medicinal plant species such as Artemesia afra, Elyptropappus rhinocerotis, Galenia africana, Hypoxis hemerocallidea, Siphonochilus aetheopicus, Sutherlundia frutescence, Tulbaghia violacea and Tulbaghia alliaceae for this study. For the in vitro study, indigenous medicinal plant extracts were prepared at twofold dilution concentrations and combined with kresoxim-rnethyl at concentrations of 0.25 and 0.5% (w/v). The B. cinerea mycelial plug assays showed potent antifungal inhibitory effects with the plant extract and kresoxim-rnethyl mixtures. Further analyses of the mixtures indicate synergistic effects between the fungicide and plant extracts. I surmise that these in vitro effects are also achievable in vivo. Combinations of these agents represent an attractive avenue for the development of new management strategies for controlling B. cinerea in the future. A second study was conducted to analyse the final dose rates for synergistic reactions for combinations of kresoxim-methyl and medicinal plant extracts against B. cinerea in vivo. A series of two-fold concentrations of medicinal plant extracts were combined with kresoxim-methyl to conduct decay inhibition studies on Granny Smith apples. Synergistic effects were observed for many of the kresoxim-methyl and plant extract combinations. I, therefore, came to the conclusion that indigenous South African plant species produce modulators that potentiate the activity of fungicides. Whether these synergistic effects are due to the inhibition of fungal multi-drug resistant pumps require further studies at the molecular level. However, these inhibitory effects are likely to be advantageous for developing fungicide formulations and application strategies with low toxicity effects on the environment. This approach not only makes it possible to reduce fungicide concentrations while maintaining adequate decay control, but also ensures a reduction of the chemical residue on the fruit.
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    Synergistic effects of mixtures of the kresoxim-methyl fungicide and medicinal plant extracts in vitro and in vivo against Botrytis cinerea
    (University of the Western Cape, 2005) Knowles, Cindy-Lee; Klaasen, J.; Johnson, Q.
    The fungus Botrytis cinerea is an opportunistic pathogen on a wide variety of crops, causing a disease known as grey mould through infections via wounds or dead plant parts. Synthetic fungicides for controlling this disease are fast becoming ineffective due to the development of resistance. This, coupled with consumers' world wide becoming increasingly conscious of potential environmental and health problems associated with the build-up of toxic chemicals, (particularly in food products), have resulted in pressure to reduce the use of chemical pesticide volumes as well as its residues. An emerging alternative to random chemical synthesis is the study and exploitation of naturally occurring products with fungicidal properties. One group of compounds known as strobilurins produced by Strobilurus species, woodland basidiomycete fungi, is a good example of this phenomenon. Plants produce an enormous array of secondary metabolites, and it is commonly reasoned that a significant part of this chemical diversity serves to protect plants against plant pathogens. A problem with plant-produced compounds as potential fungicides is that in the natural state, they are generally only weakly active compared to synthetic fungicides. There have been reports on the uses of mixtures of synthetic fungicides for the control of plant pathogenic fungi. When utilized in two-way mixtures, such fungicides may maintain or enhance the level of control of a pathogen at reduced rates for both components utilized in combinations, or alone at normal rates. These studies provide an important precedent for the idea of synergism. For this study, we hypothesize that the addition of plant extracts may enhance the antifungal efficacy of the synthetic strobilurin fungicide, kresoxim-rnethyl against B. cinerea. We selected South African medicinal plant species such as Artemesia afra, Elyptropappus rhinocerotis, Galenia africana, Hypoxis hemerocallidea, Siphonochilus aetheopicus, Sutherlundia frutescence, Tulbaghia violacea and Tulbaghia alliaceae for this study. For the in vitro study, indigenous medicinal plant extracts were prepared at twofold dilution concentrations and combined with kresoxim-rnethyl at concentrations of 0.25 and 0.5% (w/v). The B. cinerea mycelial plug assays showed potent antifungal inhibitory effects with the plant extract and kresoxim-rnethyl mixtures. Further analyses of the mixtures indicate synergistic effects between the fungicide and plant extracts. I surmise that these in vitro effects are also achievable in vivo. Combinations of these agents represent an attractive avenue for the development of new management strategies for controlling B. cinerea in the future. A second study was conducted to analyse the final dose rates for synergistic reactions for combinations of kresoxim-methyl and medicinal plant extracts against B. cinerea in vivo. A series of two-fold concentrations of medicinal plant extracts were combined with kresoxim-methyl to conduct decay inhibition studies on Granny Smith apples. Synergistic effects were observed for many of the kresoxim-methyl and plant extract combinations. I, therefore, came to the conclusion that indigenous South African plant species produce modulators that potentiate the activity of fungicides. Whether these synergistic effects are due to the inhibition of fungal multi-drug resistant pumps require further studies at the molecular level. However, these inhibitory effects are likely to be advantageous for developing fungicide formulations and application strategies with low toxicity effects on the environment. This approach not only makes it possible to reduce fungicide concentrations while maintaining adequate decay control, but also ensures a reduction of the chemical residue on the fruit.