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Olivier Cerf - Articles and news items

Persistence of listeria monocytogenes in equipment and premises

Issue 6 2011  •  4 January 2012  •  Brigitte Carpentier, Senior Scientist, ANSES and Olivier Cerf, Professor Emeritus, Alfort Veterinary School

Severe listeriosis (which can cause meningitis, septicemia, or still birth) is an infrequent foodborne illness. Yet, because of its high lethality (between 15 and 30 per cent) its causal agent, Listeria monocytogenes, is perceived as a major threat. Outbreaks of listeriosis were not overly common over the last 30 years, but they caused fear for the general population. In spite of strict regulations and the numerous precautions taken by the food business operators in Europe, and after a sharp decrease of incidence from 1987 to 2002, the number of cases per year again began to increase over the last five years. Therefore, two questions need to be asked: how can L. monocytogenes persist in food industry equipment and premises and cause the contamination of food, and what measures could be taken to combat its persistence?

L. monocytogenes is able to grow within a large temperature range (between slightly below 0°C and 45°C), over a large pH range (4.6 to 9.5) and at relatively low water activity (0.90). It can therefore grow in almost any food premises and equipment. The installation of L. monocytogenes is likely the easiest in refrigerated locations where the majority of other bacterial species cannot multiply. By using DNA fingerprinting methods, it has been extensively demonstrated that strains of L. monocytogenes may be repeatedly found for months or years in a same food processing plant. Places where L. monocytogenes are frequently found are floors, drains and more generally, locations where they find water and nutriments, even in minute amounts. What is worrying is that persistence is observed even where the cleaning and the disinfection are done right. Therefore, several researchers have hypo – thesised that persistent and sporadic strains possess different phenotypes.

Controlling Microorganisms: Problems at the food safety / risk manager interface

Issue 1 2011  •  3 March 2011  •  Olivier Cerf, Professor Emertius, Alfort Veterinary School

The present approach to food safety relies upon implementation of good hygiene practices and the application of HACCP principles against hazards in food. In use for some time almost everywhere around the world, these principles are mandatory in many countries and familiar to the European food industry.

Now, a new approach to food safety is being discussed in the context of the Codex Alimentarius Committee on Food Hygiene. It is based on an entirely different principle: instead of being targeted at hazards in foodstuffs, it is focused on the risk, namely the likelihood and magnitude of impact on public health. Examples of risk articulation are: ‘the risk of disease D (or of mortality due to that disease) caused by the hazard H in country C is X.10-n cases per inhabitant per year’ or ‘Y.10-n per serving of food F’.


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