Abstract bachelproef 2017-2018: Screening of Listeria monocytogenes and Salmonella spp. in different food matrices in South Africa

Foodborne diseases are a global issue regarding human health due to the high incidence as well as the rate of mortality associated with them. Listeria monocytogenes and Salmonella enterica are two important foodborne pathogens. South Africa is currently experiencing a L. monocytogenes outbreak that has been identified as the largest reported one in world history. About 1000 people were infected and 200 died from this foodborne pathogen since the outbreak started in 2017. It is also known that the main cause of most hospitalizations and deaths in the world are caused by Salmonella enterica.

The aim of this study was to get a picture about how safe is the food in South Africa. Various food products such as: frozen chicken, dairy products, RTE-food and frozen vegetables, widely purchased by the South African population (especially students) and more likely to have the presence of these foodborne pathogens, were investigated.

The screening was done on the food samples by enrichment and selective plating. For confirmation a molecular identification method namely Matrix-Assisted Laser Desorption Ionisation Time-of-Flight mass spectrometry (MALDI-TOF MS) was used.

The results showed that L. monocytogenes occurs only in large numbers in the frozen chicken tested samples. S. enterica has also been found in frozen chicken but in a low percentage, comparing with L. monocytogenes. The rest of the samples were found negative to the presence of those foodborne pathogens. 

Abstract bachelorproef 2016-2017: Isolation and characterization of antimicrobial resistant bacteria from fresh produce (mushrooms, lettuce) and irrigation water in South Africa

Untreated sewage water is often used for fresh produce irrigation in South Africa. This water often contains potential human pathogenic bacteria which could be a potential food safety risk. Another risk is the antibiotic resistance the bacteria may have acquired. Baseline scientific data on the prevalence of antimicrobial resistance in potential human pathogenic bacteria, found on fresh produce or in irrigation water is generated in this study.

The bacteria found on fresh produce (mushrooms and lettuce) or in irrigation water are identified and tested for antimicrobial resistance. They are tested phenotypically by the disk diffusion test and genotypically by performing PCR to look for antibiotic resistance genes.

Only one sample from the isolates found on mushrooms is identified as a Staphylococcus species. The lettuce and water samples are tested for Extended Spectrum Beta-Lactamase producing enzymes, eighteen samples came out positive. All these isolates are resistant to the eleven antibiotics that are tested as well as the one Staphylococcus isolate found on mushrooms. Other Staphylococcus isolates found on mushrooms are used to compare the genotypic and phenotypic antibiotic resistance. The phenotypic and genotypic expressions came out to be quite different as the genotypes do not always correspond with the phenotypic expression of individual isolates.

This study shows the presence of ESBL producing and multidrug-resistant bacteria on mushrooms, lettuce and lettuce irrigation water.