Stephan Coetzee

Microbiological characterisation of southern African medicinal and cosmetic clays

The effects of traditionally used medicinal and cosmetic clays in southern Africa on selected microorganisms were studied using microbiological media. The clay pH, microchemical composition, kind of associated microorganisms and antimicrobial activity of clays against test microorganisms were determined. The clays contained varying numbers of microorganisms which ranged from 0 up to 105 CFU/g. Clay pH ranged from 2.3–8.9. Neither Escherichia coli, nor other faecal coliforms were detected. Clays of pH value of <4 displayed antimicrobial activities. Clays which were active against test microorganisms had Na2O, Al2O3, SiO2, SO3, CuO or Cl2O as major components. Microbial activity of clays was attributed mainly to low pH but cations such as Cu, Al, S or Cl and various anions might have contributed to the microbicidal effects. No antimicrobial activity was established for many of the clays commonly used in the treatment of common ailments of microbial origin.

Carriage of micro-organisms by domestic cockroaches and implications on food safety

Domestic cockroaches Blattella germanica were trapped from various homes in Gaborone, Botswana using ‘Dyroach’ traps. Isolations of bacteria, yeasts and moulds were done on external body parts and on the faecal pellets using various selective media. Body parts of cockroaches were also fixed with OsO4 vapour for 24 h, sputter coated with gold under special conditions and examined in a Phillips (1) XL30 ESEM in low vacuum mode. Awide spectrum of bacteria including common food spoilage and pathogenic organisms, such as Bacillus spp., Staphylococcus spp., Escherichia coli, Pseudomonas spp., Enterobacter spp., Klebsiella spp., Erwinia spp. Salmonella sp., Shigella sp. and Serratia spp. were isolated. Yeasts commonly associated with food spoilage, such as Pichia sp., Candida sp. and Torulopsis spp. were found on many cockroaches. In addition, various groups of moulds, some associated with food spoilage and others known to produce mycotoxins, such as Aspergillus flavus, Aspergillus fumigatus and Aspergillus parasiticus were isolated. Antimicrobial sensitivities of bacterial isolates revealed resistance patterns to various agents. Since cockroaches are prevalent in homes, particularly in food preparation areas and since their body parts and faecal pellets have been found in food storage areas, concern about their impact on food quality and safety is raised and possible control measures including education of communities on proper sanitation are suggested.RésuméDes blattes domestiques Blattella germanica ont été piégées dans plusieurs maisons à Gaborone, au Botswana à l’aide de pièges ‘Dyroach’. On a réalisé des isolements de bactéries, de levures et de moisissures à partir de plusieurs morceaux d’exuvie et des fèces en utilisant différents milieux de culture sélectifs. Des morceaux d’exuvie ont également été fixés avec des vapeurs d’OsO4 pendant 24 h, recouverts d’une couche d’or et examinés en microscopie électronique à balayage sous vide à l’aide d’un microscope Phillips (1) XL30 ESEM. On a réussi à isoler un vaste spectre de bactéries comprenant des organismes pathogènes et présents dans les déchets de nourriture tels que Bacillus spp., Staphylococcus spp., Escherichia coli, Pseudomonas spp., Enterobacter spp., Klebsiella spp., Erwinia spp., Salmonella sp., Shigella sp. et Serratia spp. Des levures fréquemment associées aux déchets de nourriture, telles que Pichia sp., Candida sp. et Torulopsis spp. ont été trouvées sur plusieurs blattes. De plus, plusieurs groupes de moisissures, certains associés aux déchets de nourriture, d’autres connus pour produire des mycotoxines tels qu’Aspergillus flavus, Aspergillus fumigatus et Aspergillus parasiticus ont été isolés. Des tests de sensibilité aux antibiotiques appliqués à plusieurs isolats bactériens ont permis la mise en évidence de forme de résistance à différents antibiotiques. Dans la mesure où les blattes sont très communes dans les habitations, en particulier sur les lieux de préparation des aliments et où leurs exuvies et leurs fèces ont été trouvés dans les lieux de stockage de la nourriture, on a pumontrer l’importance de leur impact sur la qualité et l’innocuité de la nourriture, imaginer des mesures de prévention et suggérer l’éducation des communautés sur des mesures sanitaires adaptées.

Aspects of floodplain deposition in semi-arid ephemeral rivers, examples from the Kuiseb river valley, central Namibia †

Topographic and sediment work in the Kuiseb river, currently an ephemeral stream in central Namibia, has shown that floodplain deposition took place mainly downstream from zones of significant external sediment input. Two floodplain types are identified as floodplain islands which developed as braided river deposits in the midstream section of the river, and infill deposits developed from anastomosing streams in the downstream section. The two types are dependent on the geometry of the river cross section and the amount of sediment available. The topography, sediment content (fine sand and silt units) and structure all imply the deposition of floodplain deposits under wetter conditions. Particle size analysis of floodplain silts in relation to river bed and sand dune silt, indicates a closer association between the floodplains and Quaternary Homeb deposits. These data suggest that the floodplains likely formed under locally wet conditions which eroded the Quaternary Homeb deposits during the early-mid Holocene.