Food microbiology: we ignore it at our peril

We need to be constantly aware of the importance of microorganisms in our foods, says Dr Roy Betts.

It is tempting to believe that we are now aware of all of the microbiological problems that we face in our foods and are well prepared to understand and tackle them. Public health statistics tell us otherwise, and give us a warning that we ignore food microbiology at our peril. 

Recent data from 2009 suggests around 25% of the UK population suffers from food poisoning every year, and that this figure was 43% higher than it was in the early 1990s, although improved diagnosis and reporting may have some impact on this figure. 

The organism causing the biggest issue is Campylobacter; although this organism was first observed in the late 19th Century, it was not recognised as a major food pathogen until the 1970s. It is now acknowledged as the biggest cause of outbreaks of food poisoning in the UK. Its source is predominantly poultry and recent figures suggest that 59% of UK retail poultry is contaminated. However it is not hard to kill the organism, proper cooking will do it easily. In recent years the issue of undercooking and a keenness to serve items such as chicken pate in an undercooked format has exacerbated the issue. 

Salmonella has long been recognised as a cause of food poisoning and in the 1990s its presence on poultry and eggs was a major issue. However, interventions in poultry breeding and vaccinations of poultry flocks against Salmonella have substantially reduced the issue in these foods. It is, however, continuing to cause problems in other foods, particularly those that have a low moisture content, such as dried spices, nuts, seeds etc. In such conditions Salmonella will not grow, but it survives and is still able to infect consumers, contaminate other foods and it has become clear that Salmonella, like many other organisms, becomes much more resistant to heating when it is in low moisture conditions, so 'normal' cooking temperature of eg 70 to 80°C, will not affect it. 

But what of other 'newer' organisms. Listeria monocytogenes was not considered a food related problem until the 1980’s. The unique nature of this organism is its ability to grow at temperatures as low as 0°C, potentially causing issues in even well refrigerated foods. While not causing great numbers of illnesses, perhaps only 250 per year in the UK, approximately 25% of people will die from the infection, so it is an organism to take very seriously. 

Even more recently we have seen the rise in importance of the pathogenic Escherichia coli. It was in the 1990s that E.coli O157 was identified as a potent pathogen usually associated with minced beef. We now understand that the O157 strain is one of many hundreds of pathogenic E.coli known as Shiga Toxin producing E.coli (STEC) that can cause severe illness. They have been found in meats, raw dairy products and even fresh produce. 

In 2011 in Germany one strain, E.coli O104 caused around 4000 cases of illness and 50 deaths. The strain had not previously been recognised as a problematic pathogen; the issue was traced back to sprouted fenugreek seeds used raw in salads. Since then in the UK, STEC outbreaks have also been linked to handling potatoes and eating watercress. 

So what of the future? So far consideration has been given only to bacterial pathogens but we are now able to more fully understand the role of viruses in foodborne illness. It has recently been estimated that Norovirus causes around 200,000 cases of illness in England and Wales every year. Some will be due to person to person spread but perhaps something over 20,000 cases will be foodborne. This virus has been associated with raw shellfish in the past, but its link to eating fresh produce is now being considered. The virus is highly infective and the consumption of just 10 virus particles can cause illness, the major symptom of is vomiting which can spread the virus still further and infect more people. Hepatitis A and E can also be  foodborne. Hep A is associated with similar foods to Norovirus, but Hep E has recently been linked with pork products and has been reported to have a degree of heat resistance. 

What can we conclude from this? Firstly that we need to be constantly aware of the importance of microorganisms in our foods. New research and the development of new testing methods expand our knowledge of what causes issues, and what could become a problem in the future. None of the organisms in this article are difficult to control and eliminate from foods, the design of recipes and processes that keep foods safe can be straightforward. 

However, lack of knowledge of such organisms and their controls leaves the potential for food safety failures to occur. Additionally, we live in a time when the pressure to modify products is great, this can be problematic for product stability. If we change anything about our food, eg the type of cooking used, levels of preservative, salt, sugar, the type of package, or even the way we consume it, then this may alter the delicate balance between microbiological stability and safety, and instability resulting in the survival and growth of organisms causing spoilage and potentially illness. 

Understand what keeps a food microbiologically safe and stable, maintain safety controls, and never make changes unless they have been fully microbiologically validated, this should result in control over pathogens and safe food products. 

This whole area of New Issues will be included in the Hot Topics in Food Microbiology Conference at CampdenBRI on 28-29th October 2014.

Dr Roy Betts, Head of Microbiology, CampdenBRI. Chipping Campden, Gloucestershire, UK. 

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