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Pretoria study flags listeria in beef

A recent investigation has red-flagged the food-borne pathogen, listeria monocytogenes, in beef and its products across Gauteng, Mpumalanga and North West Provinces, with experts emphasising the need for strict surveillance of all processes in the production chain.

Led by the University of Pretoria (Faculty of Veterinary Science in collaboration with the Agricultural Research Council-Onderstepoort Veterinary Institute), the research found that 4.6% of chilled carcasses from seven abattoirs in one province tested positive for listeria, reports IOL.

Listeria monocytogenes causes listeriosis, which can lead to miscarriages and stillbirths, and with most human infections stemming from ready-to-eat foods.

The pathogen thrives even in refrigerated conditions, typically used to deter spoilage.

Highlighting the risks, Dr Rebone Moerane, head of UP’s Department of Production Animal Studies, said: “Processed foods can be contaminated through various means, including contact with equipment, handling of raw ingredients, or even in post-processing environments where the bacteria can persist despite regular disinfection.”

The research initiative was funded by Red Meat Research and Development SA, prompted by the 2017-2018 listeriosis outbreak in South Africa. In that instance there were more than 1 000 confirmed cases and 216 fatalities.

Processed foods, especially polony, were believed to be the primary culprits at the time.


The researchers found that the risk of exposure of cattle to listeriosis on farms was minimal, but said the detection of 4.6% of chilled carcasses sampled at Gauteng abattoirs, which were contaminated with listeria monocytogenes, was troubling, as were the findings at retail outlets.

“The prevalence of the pathogen was 6%, 8.3% and 9.3% in beef and beef products sampled in outlets in North West, Mpumalanga and Gauteng respectively, and 4.3%, 11% and 9.3% for cold beef and beef products,” Moerane said.

Some of the contaminated products were ready-to-eat items, including polony (6.9%-16.7%) and biltong (3.6%-10.3%). This increases the risk of human exposure to the pathogen as the meat isn’t cooked.

Fortunately, the researchers observed that in most cases, all of the Listeria monocytogenes isolates responded to penicillin, ampicillin and sulfamethoxazole-trimethoprim (SXT), which are important antimicrobials used in the treatment of listeriosis.

“However, the high occurrence of multi-drug-resistant strains of Listeria monocytogenes cannot be ignored, as they may pose therapeutic challenges,” said Professor Abiodun Adesiyun, an extraordinary professor in the department, who was part of the team, along with Dr Nomakorinte Gcebe of the ARC-OVI, and four postgraduate students.

Adesiyun cautioned. “This is because of the potential transfer of resistance within and between bacterial species.”

Moerane said the findings indicated serious challenges and that “we really need to take actions and interventions”.

He said that part of the problem was that the country’s legislation – and its meat laws – was fragmented.

“At abattoirs, the veterinary services are under the Department of Agriculture, but by the time the meat leaves the abattoirs, it becomes the responsibility of Health, and particularly municipalities.

“Our biggest concern is more at retailer level. What is happening… we don't have a clue. Are municipalities implementing the right measures – doing proper inspection? And surveillance monitoring?”

The research methodology of the study – published in the Journal of Food Safety – was exhaustive. Samples were collected from cattle farms, including faeces, feed, silage and water. Additionally, swabs from carcasses at abattoirs and samples from retail beef products were analysed.

Some detected serotypes of listeria monocytogenes were from groups known to cause human listeriosis. The frequency of virulence genes, indicators of the pathogen's ability to cause disease, varied across provinces, but reached alarming levels in some areas.

Study details

Contamination of beef and beef products by Listeria spp. and molecular characterization of L. monocytogenes in Mpumalanga

Khomotso C. Moabelo, Nomakorinte Gcebe, James Gana, Yusuf Ngoshe, Abiodun Adesiyun.

Published in Journal of Food Safety on 29 March 2023


This study determined the prevalence, risk factors, and molecular characteristics of Listeria species detected in beef and beef products sampled in Mpumalanga province, South Africa. Four hundred beef and beef products were collected from 30 retail outlets in three districts (Bronkhorstspruit, Emalahleni, and Middelburg) within the province. Standard bacteriological and polymerase chain reaction (PCR) assays were used in the study. The overall prevalence of L. monocytogenes and other Listeria spp. in the samples was 8.3% (33/400) and 30% (120/400) (p < .05), respectively. For the five variables investigated, statistically significant effects were evident only for the region (p < .001) and type of product (p < .0001) for L. monocytogenes, the type of outlet (p = .011) and the type of product (p < .0001) for Listeria spp. Of the 20 types of beef and beef products tested, 15 (75%) and 17 (85%) were contaminated by L. monocytogenes and Listeria spp., respectively (p = .429). Among the four categories of products tested, the prevalence of L. monocytogenes was 7.3% (8/109), 10.6% (11/104), 7.5% (8/106), and 7.4% (6/81) for raw beef, ready-to-eat (RTE) products, milled beef, and offal & organs, respectively (p > .799). Among the 33 L. monocytogenes isolates, PCR genoserogroup IIa (42.4%, 1/2a-3a) was most frequently detected. All (100%) of the isolates carried one or more of the eight virulence-associated genes assessed, with genes inlC and inlJ detected in all the isolates. The overall prevalence of L. monocytogenes (8.3%) and the high frequency of virulent serogroups of L. monocytogenes commonly associated with human listeriosis pose a food safety risk to consumers of beef and beef-based products contaminated by L. monocytogenes.


Journal of Food Safety article – Contamination of beef and beef products by Listeria spp. and molecular characterization of L. monocytogenes in Mpumalanga, South Africa (Open access)


IOL article – Alarm bells sounded as University of Pretoria study reveals concerning findings on Listeria in beef (Open access)


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