Taking on a grand challenge

Mike Peck discusses one of the grand challenges facing the UK – food safety. He thinks to meet it we need to understand bacterial pathogens

One of the grand challenges facing the UK and other nations is that of food security and food safety. The challenge is concerned with ensuring that all people, at all times, have access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life. This will require:

(i) Reducing the present level of foodborne illness. In the UK alone, food poisoning presently affects about a million people per annum, with an annual economic cost of more than £1 billion, and significant morbidity and mortality.

(ii) Ensuring the future sustainable supply of safe foods. This will include meeting consumer demand for greater food choice including higher quality foods, and providing food for an increasing number of susceptible groups (such as the elderly) that require products made to a higher safety specification. This will need to be achieved against a background of climate change, increased global population – predicted to increase from seven billion to nine billion by the middle of this century – and potential limiting resources (e.g. water, minerals, energy).

[caption id="attachment_28047" align="alignright" width="200" caption="Clostridium botulinum spore"][/caption]

Meeting the grand challenge of food security and food safety requires not only innovation to increase food chain resilience, but also a greater understanding of the behaviour of bacterial foodborne pathogens – in particular the molecular mechanisms they employ that enable their survival and growth in the food chain – to underpin the development of knowledge-led intervention strategies.

The Institute of Food Research (IFR) has an outstanding record in delivery of research outputs that support national and international industry and regulation. Research at IFR on microbiological food safety is focused on understanding how three major foodborne bacterial pathogens of the greatest concern to the UK (Salmonella, Campylobacter and Clostridium botulinum) survive and grow in the food chain. Salmonella and Campylobacter are both enteric zoonotic pathogens that cause infection, and are a major cause of morbidity and mortality worldwide. C. botulinum is a highly dangerous spore-forming bacterium that is responsible for botulism, a severe and deadly disease.

In part due to its ability to thrive and quickly adapt to the different environments in which it can grow, Salmonella remains a serious cause of food poisoning in the UK and throughout the EU. New research involving a team of IFR scientists has taken the first detailed look at the molecular mechanisms employed by Salmonella that enables their survival and growth in the food chain. Importantly we have determined how Salmonella adapts when it enters a new environment, which could provide clues to finding new ways of reducing transmission through the food chain, and thus preventing human illness.

The cells sense their new environment remarkably quickly, with more than 500 specific genes turned on in the first four minutes, and more than 900 genes turned on within 20 minutes

Bacteria can multiply rapidly, potentially doubling every 20 minutes in ideal conditions. However, this exponential growth phase is preceded by a period known as lag phase, where no increase in cell number is seen. Lag phase was first described in the 19^th Century, and was assumed to be needed by bacteria to prepare to exploit new environmental conditions. Beyond this, surprisingly little was known about lag phase, other than that bacteria are metabolically active in this period. But exactly what are bacteria doing physiologically during this period?

[caption id="attachment_28048" align="alignleft" width="200" caption="Salmonella typhimurium"][/caption]

To fill in this knowledge gap, researchers at IFR  – funded by the Biotechnology & Biological Sciences Research Council (BBSRC) and Campden-BRI, including two BBSRC/Campden-BRI-funded CASE PhD students – have developed a simple and robust system for studying the biology of Salmonella during lag phase. In this system, lag phase lasts about two hours, but the cells sense their new environment remarkably quickly, with more than 500 specific genes turned on in the first four minutes, and more than 900 genes turned on within 20 minutes. These genes encode various biosynthetic and metabolic activities, including some that control the uptake of specific nutrients.

For example, one nutrient accumulated is phosphate which is needed for many cellular processes such as energy metabolism, and we found that a gene encoding a phosphate transporter was the most highly up-regulated gene during the first four minutes of lag phase. The cellular uptake mechanisms for iron were also activated during lag phase, and are needed for key aspects of bacterial metabolism. This increase in iron concentration within the cell leads to a short term sensitivity to oxidative damage. Manganese and calcium are also accumulated in lag phase, but are lost from the cell during exponential growth.

This new understanding of Salmonella metabolism during lag phase show how rapidly Salmonella senses favourable conditions and builds up the materials needed for growth.

Future research to work out the regulatory mechanisms behind these processes, and the switch from lag phase to exponential growth, will tell us more about how Salmonella can flourish in different environments, and could point to new ways of controlling its transmission in the food chain.

Further information Details of this research were recently published in Journal of Bacteriology 194:686-701 doi: 10.1128/JB.06112-11

The Author Mike Peck from the Institute of Food Research

Contact Institute of Food Research, Norwich Research Park, NR4 7UA, Norwich, UK