Microbiology - Articles and news items

HACCP: The rise of the prerequisites

Latest issue / 4 January 2012 / John Holah and Edyta Margas, Campden BRI and Robert Hagburg, Benjamin Warren, Judy Fraser-Heaps and Sara Mortimore, Land O’Lakes

This article introduces concepts and ideas about the nature and potential control of microbiological cross-contamination in a food manufacturing environment. The concepts and opinions shared do not necessarily represent the policies and/or programs used by the companies represented by the authors.

Microbiological cross-contamination has been a contributing factor to several well-documented outbreaks of foodborne illness1,2. In most HACCP or other hazard analysis-based food safety systems, cross contamination is controlled and managed predominately by prerequisite programs (PRPs). PRPs can be defined as the measures that provide the basic environmental and operating conditions in a food operation that are necessary for the production of safe and wholesome foods3, such as cleaning and disinfection and personnel hygiene. The implementation of an appropriate PRP is also seen as the foundation on which a good HACCP plan is built and there are many examples of best practice to follow for each prerequisite (PR) at an international level4, via retailers requirements5 or from recognised food research bodies6-8 or trade associations9,10.

There is little information, however, on how to align the use of specific PRs to control actual routes of cross-contamination in food pro – cessing plants. (more…)

Persistence of listeria monocytogenes in equipment and premises

Latest issue / 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. (more…)

Predictive modelling of microbial behaviour in foods: an industrial perspective and applications

Issue 5 2010 / 5 November 2010 / François Bourdichon & Mohamed Hedi Ben Cheikh, Food Safety Centre, Danone Corporate

Mathematics is everywhere. One might go into the field of biology to avoid numbers and equations, yet they are still there, helping food technologists to decipher the behaviour of micro-organisms in different food matrices and along the process chain. Since the negation of the spontaneous generation theory by Louis Pasteur in the 19th Century, the different phases of bacterial growth have been well defined: lag phase, exponential phase, stationary phase. Yet this simplistic approach of molecular mechanism isn’t that easy to model through polynomial equation, when taking into consideration the food matrix and role of preservative factors. (more…)

FISHing for pathogens: Rapid detection of whole microbial cells in foods

Issue 3 2010, Past issues / 30 June 2010 / Byron Brehm-Stecher, Assistant Professor, Rapid Microbial Detection and Control Laboratory, Iowa State University

Today’s food production and distribution networks are extremely efficient. We are able to move food from the field to the table rapidly and effectively – on a global scale – under conditions that maximise quality, visual appeal and nutritional content. Unfortunately, toxigenic or infectious microbes may also come along for the ride at any number of points along this farm-to-fork journey. As we have seen with recent incidents in the United States, contaminated ingredients provided to large food companies by relatively small niche players can wreak havoc throughout the food chain. (more…)

Microbiological safety of chocolate confectionery products

Issue 4 2009 / 12 December 2009 / Anett Winkler, Corporate Microbiology, Kraft Foods R&D

For many years, low moisture foods, such as chocolate, were regarded as microbiologically safe due to the inherent product characteristics. Water activity levels below 0.6 would prevent any microbial growth, whereas water activities below 0.85 would prevent proliferation of pathogenic / toxin formation by toxigenic microorganisms[1]. A water activity of >0.6 and <0.85 would potentially allow for xerophilic yeasts / moulds growth that are of importance in spoilage of those foods. In addition to the low water activity, other antimicrobial parts of the ingredients had been thought to contribute to the microbiological safety of those products[2].

It was in the early 1970′s when the first outbreaks of Salmonella could be traced back to low moisture products, especially chocolate[3,4]. Since then, several low moisture foods have been implicated in outbreaks: oat cereals[5], flavoured potato chips[6], peanut butter[7], Halva (Tahini)[8] and infant formula[9]. In all cases, Salmonella was the microorganism causing the disease, thus making it the main pathogen of concern for those foods[10]. Further analyses and investigations of the involved foods revealed that in low moisture foods, very minute amounts of living Salmonella seem to be sufficient to cause illnesses. Data from outbreaks suggest the concentration of Salmonella in the implicated foods was as low as 0.005 CFU/g of product[11]. One common property of foods that exhibited this unusually low infective dose was low moisture and high fat where the cells were embedded in a fatty matrix. This combination of properties allowed the Salmonella to pass through the stomach[12] whereby they infected the intestine. In addition to the low infective dose studies showing the survival of pathogens in confectionery products, raw materials demonstrated long term survival, over a period of several months, in these matrixes[13,14]. (more…)

Strategic considerations in choosing a rapid method

Issue 1 2008, Past issues / 28 February 2008 / Dr. John D. Marugg, Nestlé Research Centre, Quality and Safety Department, Microbiological Safety Group, Switzerland

Food manufacturers face challenges in optimising speed and efficiency, reducing product inventory, simultaneously responding to microbiological and chemical contaminants and entering the production process, via ingredients or the environment. Currently, most official or reference methods for pathogen or contaminant detection are laborious, costly, and often take a long time (3-7 days or longer) to obtain results. The application of rapid methods allows for an easy and fast response in the monitoring of raw materials and production environments, reducing the turn-around-time along the supply chain.

(more…)

Use of predictive microbiology in the food industry

Issue 4 2007 / 16 November 2007 / Jeanne-Marie Membré, Unilever

The goal of predictive microbiology is to provide useful predictions about the microbial behaviour in food systems. Predictive microbiology combines “the disciplines of food microbiology, engineering and statistics” (Schaffner and Labuza, 1997). (more…)

Luminescent techniques for microbiological analysis of foods

Issue 1 2007, Past issues / 7 March 2007 / Dr. Mansel Griffiths, Canadian Research Institute for Food Safety, Canada

There are many naturally bioluminescent organisms existing in nature and the mechanisms whereby some of these creatures emit light have been fully characterised1. These include the luciferin-luciferase system of bacteria, insects (fireflies and click-beetles) and the jellyfish Aequorea victoria. In essence, bioluminescence involves the conversion of chemical energy into light energy by an enzyme, commonly termed luciferase.

(more…)

A prime example

Issue 4 2006, Past issues / 6 November 2006 / Graeme Jardine, Microbiology Laboratory Manager, RHM Group Ltd

Technological advances in the field of food microbiology are a common occurrence. A great deal of research and validation is put into improving established methodologies and utilising new rapid approaches to isolation and detection. However, established ‘conventional testing’ is still the main stay of most food microbiology laboratories with the age old traditions of putting samples on petri dishes. RHM Technology is one of a small number of UK labs that have employed a high-tech approach to this area of testing, in order to bring improved service level and cost benefit.

(more…)

Listeria monocytogenes – a recent history

Issue 3 2006, Past issues / 11 August 2006 / P A Voysey, Campden and Chorleywood Food Research Association

Listeria monocytogenes is a pathogenic bacterium and one of six species belonging to the genus Listeria. This species is the only one believed to be pathogenic to man; however, not all L. monocytogenes serotypes have been linked with illness. The bacterium is very common in the environment. It has been found in at least 37 mammalian species, as well as 17 species of birds and possibly some species of fish and shellfish. It can be isolated from soil, silage and other environmental sources. L. monocytogenes is quite hardy and resists the effects of freezing, drying and heat remarkably well for a bacterium that does not form spores.

(more…)

Detecting Salmonella antibodies in pork

Issue 4 2005, Past issues / 21 November 2005 / René Achterberg, Judith Maneschijn-Bonsing, Rinus Bloemraad, Manon Swanenburg and Kitty Maassen, Animal Sciences Group, Lelystad, The Netherlands

Programs for monitoring Salmonella in the pork production chain have begun in several European countries. For an assay to be used in a monitoring program, it is a prerequisite that the total testing time per sample is short and that regeneration is optimal. In collaboration with a major pork producer in The Netherlands, a pilot study for herd screening was conducted to compare the performance of two immunoassays for the detection of antibodies directed to Salmonella sero-groups B and D in porcine sera in a routine setting.

(more…)

The benefits of automated pathogen testing

Issue 2 2005, Past issues / 3 May 2005 / Eric Maucci, Food Hygiene Technical Manager, Laboratoire Inter-Départemental des Analyses Laitières (LIDAL)

Renowned for its ‘postcard’ lake-side setting surrounded by snow-capped mountains, the beautiful French town of Annecy is perhaps less well known as the home of famous regional raw cows’ milk cheeses, such as Reblochon and Tomme. Controlling the quality of these cheeses and the raw milk used to produce them, is the daily task of the Annecy-based reference laboratory, LIDAL.

(more…)