Browsing by Author "Keet, Rochelle"
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- ItemCategorization of Listeria monocytogenes from food, environmental, and clinical origin in the Western Cape (South Africa)(Stellenbosch : Stellenbosch University, 2020-04) Keet, Rochelle; Rip, Diane; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: Listeria monocytogenes is a ubiquitous food pathogen responsible for the often-fatal infection, listeriosis. Foods that act as vectors of L. monocytogenes include meat products, seafood and fish products, dairy products, and ready-to-eat (RTE) foods. South Africa recently experienced the largest ever listeriosis outbreak during 2017-18, and despite this, information on L.monocytogenes is still lacking. Internationally, there is a high incidence of L. monocytogenesresistance towards antibiotics currently used as a treatment for listeriosis. However, in South Africa there is little information available on the resistance patterns of L. monocytogenes to these antibiotics. Additionally, due to the difficulty in controlling L. monocytogenes in the food processing environment, new methods such as bacteriophage treatment are being investigated to reduce L. monocytogenes numbers in these environments. Worldwide, studies have demonstrated the efficacy of bacteriophages against L. monocytogenes, but in South Africa, this technology is still unfamiliar and untested. Seeing as South Africa has a high burden of serious diseases, such as tuberculosis and HIV/AIDS, which often amplify the impacts of listeriosis, data on the efficacy of phage treatment, as well as currently used antibiotics, against L. monocytogenes, is greatly needed. Using L. monocytogenes isolates from various origins (Clinical, Environmental, Raw meats, Raw seafood, and RTE) in the Western Cape, South Africa, the first objective was to classify L.monocytogenes isolates into lineage groups by using a recently developed PCR-RFLP method(based on SNPs within the hlyA gene). The results showed an overrepresentation of Lineage I in Clinical environments and Raw seafood, while in the Environmental, Raw meats, and RTE categories, Lineages I and II were somewhat equally distributed. The prevalence of a high number of Lineage I isolates in categories other than Clinical contrasts with previous evidence that Lineage I is mostly associated with human listeriosis, while Lineage II is mostly associated with foods. The second objective was to determine the susceptibility of L. monocytogenes isolates to a commercial bacteriophage (ListexTM P100), using spot tests. Additionally, the lineage group data was used to determine whether or not lineage classifications influenced bacteriophage susceptibility. The L. monocytogenes isolates from the Clinical, Environmental, Raw meats, and Raw Seafood categories were significantly susceptible to phage activity. However, a large fraction of isolates in the RTE category were tolerant to the phage, which disagrees with the findings of others. Additionally, both lineage groups were significantly susceptible to phage activity when considering all categories combined and lineage grouping did not significantly influence phage susceptibility. The final objective was to determine the antibiotic resistance of L. monocytogenes isolates to five antibiotics, namely ampicillin, chloramphenicol, erythromycin, gentamicin, and tetracycline, using the disc diffusion method (EUCAST). The results indicated that all isolates were significantly susceptible to ampicillin, and many isolates were resistant to chloramphenicol, erythromycin, and tetracycline. Clinical and Raw seafood isolates were significantly susceptible to all antibiotics, while Raw meats had the highest number of resistant strains.