Listeria monocytogenes - South African Outbreak - Microchem
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Listeria monocytogenes – South African Outbreak

Listeria monocytogenes – South African Outbreak

In recent months the National Institute for Communicable Diseases (NICD) has received reports of a distinct increase in the number of Listeria monocytogenes pathological isolations in South Africa. The increase has been noted in both public and private sectors with the most notable increase in the Gauteng Province (62%). Available data confirms 557 cases of listeriosis across the country during 2017. This indicates a 1326% increase since the same time in 2016 (Communicable Diseases Communiqué, 2017).  A significant route of transfer of L. monocytogenes is from food products destined for the ready-to-eat market. This places pressure on food producers to mitigate their risk to consumers.


What is Listeria monocytogenes?

L. monocytogenes is a facultative anaerobic Gram-positive bacterium found to be widespread in the environment and is most frequently isolated form ready-to-eat foods as L. monocytogenes has the ability to actively grow at refrigeration temperatures as low as 0 °C. This greatly increases its ability to evade control in human foodstuffs.


What is Listeriosis?

Listeriosis is an infection caused by the pathogen Listeria monocytogenes. Unlike most other foodborne pathogens, L. monocytogenes can grow in food with a fairly low moisture content, under salt stress, and at commercial refrigeration temperatures.  The ability of L. monocytogenes to persist and multiply in the food environment which include hurdle technologies contributes to the difficulty of managing the organism is the food production industry. Listeriosis impacts particular at-risk groups which include: pregnant women, the elderly, immunocompromised individuals, fetuses, and newborns.  The complication of listeriosis in these risk groups include severe sepsis, meningitis, or encephalitis, which cause lifelong consequences. Listeriosis can be fatal where infection during pregnancy can result in spontaneous abortions, stillbirths, and preterm birth.

Why is it significant?

In the last few years L. monocytogenes has become one of the most important foodborne pathogens due to its ability to provoke listeriosis, a severe and often life threatening disease in vulnerable individuals with a case fatality rate of 12.7% (2016) and an estimated 20-30% case fatality for South Africa in 2017.  Since the foodborne pathogenicity of Listeria monocytogenes was established a concerted effort has been undertaken by both the food industries and regulatory agencies regarding the control and spread of this organism in the food production, processing, distribution, and consumption chain.

Epidemiological data indicate that certain food products are more likely to be associated with listeriosis outbreaks than others. Such foods are products consisting of raw ingredients or that are eaten raw, products not subjected to a listericidal process and products that have an extended shelf life under refrigeration and allow pathogen growth and are susceptible to post-lethality contamination, particularly when intended to be consumed without further cooking by vulnerable populations.


How does L. monocytogenes survive in the processing environment?

Various factors contribute to the ability of L. monocytogenes to persist in the environment, the most prominent being their ability to attach to surfaces and initiate biofilm formation.  Using disinfectants at supplier recommended concentrations will completely inactivate L. monocytogenes in suspension, however when the biocidal chemical comes into contact with organic matter (from food debris of extra cellular biofilm matrices) it can be partly neutralised.  As such, the ability of L. monocytogenes to initiate the formation of multispecies biofilms is a mechanism of persistence and their formation occurs in areas not exposed to daily cleaning (floor & walls with crevices and cracks).  Other factors contributing to the persistence of L. monocytogenes are harborage sites that are not sufficiently cleaned (slots, drains, slicers, conveyer belts, and packaging machines) thus leading to recontamination.


What can be done?

It is recommended to limit the opportunities of contamination by preventing the persistence of L. monocytogenes through

  • Prevention of microbial attachment prevention by thorough cleaning and avoiding porous materials.
  • By preventing biofilm formation through an established and thorough deep clean procedure.

By identifying critical sites and eliminating bacteria from those sites.


How can Microchem help you?

  • Microchem offers hygiene services that includes a hygiene inspection and hygiene report personalized to your facility.
  • Microchem can assist you with environmental swabbing of your facility to identify niches where Listeria can proliferate from. Areas that are identified as possible sources of contamination can then be targeted with appropriate cleaning techniques. We also supply swabbing kits should you wish to perform the swabbing in-house.
  • We offer qualitative screening for the presence of monocytogenes in final products as well as enumeration of the confirmed L. monocytogenes isolates present.
  • Microchem offers consultation services to assist with hygiene management in your facility.
  • Microchem has close ties with experts in the field, thus staying up to date on the latest trends in research internationally.


Microchem’s Technology

Microchem uses a rapid and sensitive chromogenic test method that is AFNOR certified and validated for the detection of Listeria monocytogenes, the pathogenic strain of the Listeria species.

L. monocytogenes is isolated using selective enrichment and a specific colorimetric enzyme reaction on chromogenic media. Further confirmatory tests are performed if any presumptive colonies are isolated.

This method detects L. monocytogenes directly, is faster than traditional testing methods, while also being cost-sensitive.


Additional Information

For additional information on L. monocytogenes see our previous communications on our website: Testing for Listeria monocytogenes


Other Services by Microchem

  • Routine Food Microbiology Analyses
  • Food-borne Pathogen Analyses
  • Water Microbiological Analyses
  • Product Shelf-Life Analyses
  • Hygiene Inspections and Reports
  • Microbiological Swabbing
  • Foreign Object Inspections
  • Food Chemistry
  • Nutritional Analyses
  • Trace Elemental and Heavy Metal Analyses
  • Food Colourants (Azo Dyes)
  • Vitamin Analyses
  • Water Chemical Analyses
  • Melamine Analyses


Contact Us

Cape Town (Head Office)
1st Floor Fairweather House,
176 Sir Lowry Road
Woodstock, Cape Town, South Africa, 8001
Tel: +27 (21) 465-6996 or 061 394 1913

Microbiology Lab Manager: Ilse Liedemann,

Chemistry Lab Manager: Hannes Esterhuizen,

Pesticide Lab: William Schwartz,


Gauteng Micro Laboratory

41 Golden Drive,
Morehill, Benoni, South Africa, 1501
Tel: +27 (11) 425-3775 or 061 393 5354

Microbiology Lab Manager: Hussein Ebrahim,

Pharmaceutical Lab Manager: Brendan Moore,



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