Electronic Theses and Dissertations (Masters)

Permanent URI for this collectionhttps://hdl.handle.net/10539/38018

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Effects of acidification on the survival of pathogens in reconstituted infant formula
(University of the Witwatersrand, Johannesburg, 2023-10) Nemakonde, Mufunwa; De Maayer, Pieter
Infants are at a high risk of developing food-borne illnesses due to the consumption of powdered infant formulas (PIFs) contaminated by pathogenic microorganisms. These pathogens may be introduced during PIF production, transportation or during preparation and storage due to poor hygiene practices. Therefore, it is important to improve the microbiological safety of PIFs to reduce illness. Manufacturers have added further measures to ensure continued control of pathogenic microorganisms during the reconstitution and consumption, including the addition of prebiotics and probiotics, as well as acidification of the PIFs, which negatively affect the growth of pathogens. Different organic acids have been biologically or chemically added to commercial PIFs, however, little is known about the efficacy of the different acids in controlling pathogen growth post-reconstitution. The present study aimed to evaluate and compare the effects of two acids, namely citrate and lactate, integrated in commercial PIFs from two manufacturers on pathogen growth within the products. In Chapter 1, we present a review of the current literature pertaining to PIF production and consumption, its microbiological safety and key problem pathogens, as well as measures to control these pathogens (with specific emphasis on PIF acidification). In Chapter 2, the methodology of the present study is discussed. The effects of lactate and citrate incorporated in commercial PIFs against eight key PIF pathogens was evaluated using plate-based assays. Furthermore, the efficacy of PIF acidification at different storage temperatures and over prolonged storage periods was determined. Finally, to validate the effect of acidity on controlling pathogen growth, a spectrophotometric approach was used. Chapter 3 presents and discusses the key findings of the study. PIF acidification was found to negatively affect the growth of pathogens in comparison to the non-acidified infant formula. Acidification and storage at suboptimal temperatures resulted in little to no microbial growth. Lactate acidification of PIFs demonstrated greater inhibitory effects against most pathogens compared to citrate acidification. Further, lactate was found to have a bactericidal effect on the growth of some pathogens. Similarly, Luria Broth acidification resulted in the reduction of microbial growth. This validated that the acids and not other constituents of the infant formula were responsible for the inhibitory effect. Finally, Chapter 4 provides a summary of the key findings as well as recommendations and guidance on future studies which could be undertaken to enhance the effective control of pathogens in powdered infant formulas, thereby ensuring a safe and nutritious food source for infants.
Metagenome sequencing of the lichen species Flavopunctelia flaventior and Parmotrema tinctorum from Gauteng, South Africa
(University of the Witwatersrand, Johannesburg, 2024-06) Katane, Malebogo Dimpho; Botes, Angela; De Maayer, Pieter
Lichens are defined as a mutualistic association between fungi (mycobiont) and an algal and/or cyanobacterial photobiont. Increasing evidence suggests that lichens comprise more diverse microorganisms than initially thought, where lichens represent an interaction between archaea, bacteria, filamentous fungi, green algae, yeasts, and viruses. Not many comprehensive studies have been done of South African lichen species. The present study employed metagenome sequencing to investigate the lichen microbiomes of Flavopunctelia flaventior and Parmotrema tinctorum sampled from Bryanston, Gauteng province, South Africa. Furthermore, the roles played by the members of the lichen microbiome within symbioses were also studied by functionally annotating the assembled metagenomes of the two lichen species. This study sets the groundwork for future studies on South African lichen species. In Chapter 1, an extensive literature review on lichens, their ecology, taxonomy and biology is discussed. Furthermore, it delves into the existence and shape of the microbiome beyond the mycobiont and the photobiont. Additionally, possible roles that the lichen microbiome may play in sustaining the lichen symbiosis is also discussed. In Chapter 2, the metagenomes of two lichen species were sequenced, the quality of the reads were assessed, and taxonomic classification was performed to elucidate the composition of microorganisms associated with each lichen species. Both microbiomes were dominated by bacteria, with limited fungi, viruses, and archaea. The majority of the identified phyla and genera were found to be common between the two lichen species. Similarities in the core microbiome was accounted for by the fact that F. flaventior and P. tinctorum were sampled from the same location and they are both members of the Parmeliaceae family. In Chapter 3, the metagenomic reads were assembled and functionally annotated using various bioinformatics tools. We demonstrate that the members of the lichen microbiome are involved in the cycling of nutrients such as carbon and nitrogen. We also found differences in carbon fixation pathways, which were attributed to the accessory microbiome. Finally, a summary highlights key results and recommendations on future work that could be undertaken to further provide insight into biological pathways essential to sustain the lichen symbiosis.
The genome sequence of the Yellow-billed Duck (Anas undulata)
(University of the Witwatersrand, Johannesburg, 2024-01) Ngxamani, Namhla; De Maayer, Pieter; Mollett, Jean
No abstract given