Scientists raise alarm about potential listeriosis outbreak in beef products in SA

Scientists have warned of a possible listeriosis outbreak in beef products in South Africa.

University of Pretoria researchers have found high levels of listeria pathogens in the beef production system in Gauteng, Mpumalanga and the North West Province.

A study conducted from 2019 to 2020, by a team of experts at the University of Pretoria (UP), into foodborne pathogen listeria monocytogenes in beef and beef products at some abattoirs and retailers in Gauteng, Mpumalanga and North West provinces, has produced concerning outcomes.

“It’s our hope that government and industry stakeholders will act on these findings and introduce strict control and monitoring measures at the appropriate stages in the beef production system,” said Dr Rebone Moerane, Head of UP’s Department of Production Animal Studies.

“It’s vital that we use the outcomes of this study to get ahead of another potential outbreak of listeriosis.”

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The research by UP’s Agricultural Research Council-Onderstepoort Veterinary Institute (ARC-OVI) showed that, among other findings, 4.6% of chilled carcasses sampled at seven abattoirs in one of the provinces were contaminated with listeria monocytogenes.

This means that contaminated carcasses have the potential to enter the food chain as beef products sold at shops. Listeria is a foodborne pathogen that causes listeriosis, a life-threatening disease that could cause miscarriage and stillbirth among pregnant women, according to the research.

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Most human cases are associated with the consumption of ready-to-eat foods, and the risk of illness increases with the number of cells ingested.

“The pathogen is able to survive and multiply at the refrigerated temperatures at which foods are stored to prevent spoilage. Processed foods become contaminated by contact with equipment, the handling of raw products, or from post-processing settings in which the pathogen can survive despite the routine use of disinfectants,” said Moerane, who was part of the research team along with Professor Abiodun Adesiyun, an professor in the department, Dr Nomakorinte Gcebe of the ARC-OVI, and four postgraduate students.

“Because of potential contamination during slaughter, carcasses can become contaminated, leading to contaminated meat and meat products.

“A wide variety of foods – including beef, pork, poultry and milk-based products – have been reported to harbour the pathogen and cause listeriosis among consumers,” said Moerane.

The study, which was funded by the Red Meat Research and Development South Africa, was prompted by the 2017-2018 outbreak of listeriosis in South Africa, which led to 1 060 confirmed cases and about 216 deaths.

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Processed foods main cause of outbreak

Processed products – polony, in particular – were suspected of being the main source of the outbreak. “With this study, we sought to investigate the prevalence and molecular characterisation of pathogenic serotypes [a distinguishable strain of a microorganism] of listeria monocytogenes in beef and beef products in Gauteng, Mpumalanga, and the North West.”

Some of the strains of listeria monocytogenes detected by the team belong to serogroups which are known to have the potential to cause listeriosis in humans.

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The researchers found that the risk of exposure of cattle to listeriosis on farms is minimal.

“However, the detection of 4.6% of chilled carcasses sampled at Gauteng abattoirs being contaminated with listeria monocytogenes is troubling, as are 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 added.

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 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 Adesiyun.

The research team recommends that government and private companies implement stringent food safety measures at abattoirs and processing plants to reduce contamination and lower the possibility of another listeriosis outbreak.

The team also recommended follow-up studies of moist biltong to determine its ability to support the growth of the pathogen and assess the risk posed to consumers.