M.Tech. / Please refer to full text to view abstract

M.Tech. (Biomedical Technology) / A study was conducted to determine the extent of fungi and mycotoxins contamination of Rwandan selected food commodities. A total of one-hundred food samples including maize, rice, cassava, beans and peanuts were collected from all five provinces of Rwanda and analysed. Mycological data obtained revealed a high level of contamination of common toxigenic fungi belonging mainly to the Aspergillus, Penicillium and Fusarium genera. Accordingly, Aspergillus flavus was the most prevalent fungal contaminant in maize (90%), while A. carbonarius was mainly concentrated in peanuts at an incidence rate of 70%. Aspergillus fumigatus was mostly found in cassava (85%) in combination with Penicillium decumbens at the rate of 70%, meanwhile P. citrinum was found at an incidence rate of 80% in rice. The genus Fusarium was dominantly present with F. verticillioides and F. graminearum found in all analysed commodities. A toxigenicity study was also conducted to evaluate the capacity of these fungi recovered to produce their respective mycotoxins. Certain species such as A. flavus and A. parasiticus isolated from these commodities produced the aflatoxins (AFs). Other Aspergillus spp. such as A. carbonarius produced ochratoxin A (OTA) and F. verticillioides and F. graminearum also showed their capacity in producing different mycotoxins viz: zearalenone (ZEA), fumonisins (FBs) and deoxynivalenol (DON). The analysis of mycotoxins in these commodities was performed following thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). Data obtained revealed that peanuts and maize were the most contaminated with mycotoxins at incidence rates of 85 and 80%, respectively, and at the highest contamination levels. The highest AF-contaminated commodity was maize from Western province (range: 1.3-3219.6 μg/kg; mean: 829.3 μg/kg) followed by peanut from the same region whose mean level found was 401.5 μg/kg (range: 3.2–1755.8 μg/kg). Ochratoxin A was also found in peanuts with a mean concentration of 302.6 μg/kg, while DON was found at the highest level of 419.6 μg/kg in a rice from Kigali-city. Maize was the main substrate for FBs (mean: 134 μg/kg; max: 4591 μg/kg). Zearalenone was also recovered from samples but at a low incidence rate of 40% with the highest level of 5.2 μg/kg recorded. It was also observed that 65% of samples analysed were contaminated with more than one mycotoxin.

Magister Scientiae - MSc / Listeria monocytogenes is a Gram-positive bacterium responsible for listeriosis, a food-borne disease, which may result in severe illness and possible death. The importance of L. monocytogenes as a food-borne pathogen has been recognized since the 1980's when a correlation between the cunsumption of contaminated foodstuffs and human listeriosis outbreaks was observed. Listeriosis occurs with the ingestion of contaminated foods. The aim of this study involved developing DNA based methods to aid the food industry for the fast detection of L. monocytogenes in food products. Therefore assays were developed in such a way that they will have potential applications in the food idustry. / South Africa

Master of Science / Department of Diagnostic Medicine/Pathobiology / Steven S. Dritz / Cassandra K. Jones / Biological hazards in animal feed are a growing concern for the feed industry. Porcine epidemic diarrhea virus (PEDV) is the first viral pathogen confirmed to be transmissible in swine feed and feed ingredients. This led to investigations identifying the magnitude of transmissible risk PEDV imposes and strategies to mitigate infectivity in contaminated diets. The objective of the first experiment was to evaluate the minimum infectious dose of PEDV in virus-inoculated feed. Pigs became infected when PEDV concentrations at or above 5.6 × 10¹ 50% tissue culture infectious dose/g (TCID₅₀/g); corresponding feed cycle threshold (Ct) of 37 or below was utilized. Evaluation of a mitigation strategy for PEDV contaminated diets is also important since cross-contamination during feed manufacturing is possible. Therefore, the objective of the second experiment was to determine the effectiveness of feed batch sequencing as a method to minimize the risk of PEDV cross-contamination. This method was effective to reduce but not eliminate infectious PEDV carryover risk. Furthermore, feed that lacked detectible PEDV RNA as analyzed by quantitative real-time reverse transcription PCR assay (qPCR) was infectious. The third study was an observational study complementary to the previous experiment where the magnitude of virus contamination in the feed manufacturing facility was characterized during feed batch sequencing. Widespread contamination of the facility occurred and surfaces remained contaminated until chemically cleaned. The final experiment was conducted to assess PEDV RNA detection in feed and spray dried porcine plasma (SDPP) when analyzed by qPCR across 5 diagnostic laboratories. Overall, it appears qPCR PEDV RNA detection in feed and SDPP was precise as quantified by low coefficient of variation across laboratories, with the exception of one %CV from SDPP inoculated with low virus load from one laboratory. Although the magnitude of the Ct value difference was large in only 1 of 5 laboratories, comparisons of Ct values across laboratories should be interpreted cautiously. Finally, qPCR can be a useful surveillance tool for detection of PEDV RNA in non-clinical samples such as feed and SDPP.

South Africa currently faces multiple Cr(VI) contamination problems which are unsuccessfully remediated using available technologies. Cr(VI) is highly toxic, carcinogenic and mutagenic in nature and it is exclusively released through anthropogenic activities. A new treatment approach is proposed using locally isolated Cr(VI) reducing species of bacteria. This method is envisioned to be economical and ecologically friendly. Indigenous chromium(VI) reducing bacteria (CRBs) were isolated from a dried sludge consortium collected in the Brits Wastewater Treatment Plant, North-West Province (South Africa). Characterisation using 16S rRNA fingerprinting followed by taxonomic studies revealed a wide diversity of CRBs isolated under anaerobic conditions than under aerobic conditions. The consortium was determined to be predominantly gram-positive. The Cr(VI) reducing component of the culture was determined to be predominantly facultative, consisting predominantly of Bacillus sp., i.e. B. cereus, B. thuringiensis and B. mycoides. Batch experiments under both aerobic and anaerobic conditions showed a high Cr(VI) reducing performance under relatively high initial Cr(VI) concentrations. The reduction rate using this culture was 3 to 8 times higher than reduction rates reported in bacteria previously isolated and studied in North America and Europe. The culture performed best as a consortium with the different species operating cooperatively. The bacteria were acclimated to Cr(VI) toxicity through the long period of contact during the activated sludge treatment process at the source. A Monod like model was used to evaluate the rate of Cr(VI) reduction over a wide range of initial Cr(VI) concentrations. The model revealed that Cr(VI) reduction in the consortium culture followed quasi-first order kinetics with a Cr(VI) inhibitor term as a second exponential: C = C0 . exp [-p . exp (-q . C0 ) . t]. The parameter p and q for the semi-empirical first order model were statistically accurate with R2 values greater than 94% for all data ranges evaluated. Previous studies were not able to pick the variability of Monod coefficients, kmc and Kc, since at narrow ranges of initial Cr(VI) concentrations, the impact of the chromium toxicity variability was insignificant. This study demonstrates the potential of a biological approach using locally isolated Cr(VI) reducing bacteria to decontaminate Cr(VI) polluted sites in South Africa. / Dissertation (MSc)--University of Pretoria, 2009. / Chemical Engineering / unrestricted

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Since Actinomycetes have been isolated from finished public drinking water, it is believed that the organisms are unaffected by the chlorination and flocculation of water treatment plants and pass as spores through the filters into the general distribution system. For this reason it was deemed imperative to study the toxic effects of these organisms.

Submitted in fulfillment of the requirements for the Degree of Master of Technology: Biological Sciences at Technikon Natal, 2000. / Spice oils are known to exhibit antifungal activity and therefore have the potential to control mycotoxin production. There is a need in the food industry to find measures to control mycotoxins that are frequently associated with grains that form the staple diet of the majority of the population in South Africa. Clove, cinnamon, oregano, tumeric, eucalyptus, neem, aniseed, mace and nutmeg oils were tested to determine their inhibitory potential against growth of Aspergillus parasiticus and Fusarium moniliforme using the agar overlay technique. Varying concentrations of the spice oils, ranging from 0.1 ppm to 2.0 ppm, were incorporated into broth cultures of A. parasiticus and maize patty cultures ofF. moniliforme. Levels of production of aflatoxins and fumonisin were determined using standard thin layer chromatography and highpressure liquid chromatography methods. In addition, the active component of the spice oils were isolated, characterised and tested. The inhibitory potential of these compounds for field use was tested by incorporating clove oil, whole cloves and ground cloves in samp / M

Recent theories posit that cognitive factors explain the development and maintenance of contamination fears associated with obsessive compulsive disorder (OCD). Few studies to date have aimed to establish causality or temporal precedence for cognitions predicting OCD-relevant distress and avoidance. The current study used a prospective design to assess threat appraisals, personality traits, and obsessive compulsive symptoms in an unselected sample of university students and community members (N = 105) several days prior to a contamination behavioural approach task (BAT) in a public washroom. Results of the hierarchical regressions demonstrated that prospective danger appraisals significantly predicted both disgust and avoidance on the BAT, even when controlling for neuroticism, disgust sensitivity, and OCD symptoms. In contrast, looming germ spread appraisals and responsibility appraisals were not significant predictors of the BAT. Results from in vivo distress ratings and implicit reaction time data indicated that disgust is more strongly associated with contaminants compared with anxiety. The findings of this research suggest that psychological treatment for contamination concerns should include monitoring of disgust as a process and outcome variable in exposure paradigms, and focus on reappraisal of danger estimates related to disease in cognitive paradigms. / Arts, Faculty of / Psychology, Department of / Graduate

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