From trigger to toxin - Clostridium botulinum exposed

A discovery by Institute of Food Research (IFR) scientists is set to improve the food industry’s ability to predict foodborne botulism.

Dormant spore prior to germination and outgrowth

Botulism is a severe and often deadly disease caused by toxin-producing spores of the bacterium Clostridium botulinum. The spores remain harmless until they find a suitable, anaerobic environment in which to germinate. After germination, there is a short “lag time” until rapid cell division begins.

Lead author of the newly published study Dr Sandra Stringer said: “We set out to unravel the various stages within lag time leading to the production of deadly neurotoxin. This is like looking at the time between loading a gun and actually pulling the trigger.”

Spores are the time travellers of the bacterial world. They are produced at times of environmental stress and exist in a state of suspended animation. In the protective pod of a spore coat, they resist temperature extremes and dehydration and can survive for millions of years until conditions are ripe for germination.

A single spore of Clostridium botulinum can lead to neurotoxin production in food. Previous studies have found that the lower the number of spores, the more difficult it is to predict growth patterns. However, prediction of lag time has until now been based on the belief that the first spore to germinate will be the first to produce actively dividing cells and start toxin production.

The IFR study is the first to investigate each stage within lag time and the relationship between them.

“The only way to study each stage in detail is by using microscopy and image analysis”, said Dr Stringer. “We developed a novel imaging system and made microscopic observations of 1,739 spores. We tracked their irreversible progress through germination and rehydration to shedding the spore coat, emerging as a young cell, maturing and finally beginning cell division.

“We found that each stage from germination to growth is variable between individual spores and none of the stages are related. Germination is therefore not a good predictor to use in risk assessment work as it underestimates the time to growth and toxin production”, said Dr Stringer.

Images of individual spores were captured every five minutes for 15 hours then analysed.

“This was painstaking work, but worth it”, said Dr Stringer.

Mathematical biologist Dr Gary Barker says the findings have immediate practical benefits: “This fundamental science can be incorporated into real risk assessments for real products. Food companies can approach us for microbial risk assessments of specific products based on a model we have developed that reflects on the variability of spore lag time.”

Contact: gary.barker@ifr.ac.uk

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Notes to Editors

• Please contact Zoe Dunford for more information, images and an interview with Dr Sandra Stringer: 01603 255111 / 07768 164185 zoe.dunford@ifr.ac.uk

Background

• The mission of the Institute of Food Research (www.ifr.ac.uk) is to carry out independent basic, and strategic research on food safety, quality, nutrition and health. It is a company limited by guarantee, with charitable status, grant aided by the Biotechnology and Biological Sciences Research Council (BBSRC).

Funding came from

• This research was funded through the Biotechnology and Biological Sciences Research Council (BBSRC) competitive strategic grant to IFR with support from the EU program Quality of Life and Management of Living Resources (BACANOVA, www.ifr.ac.uk/bacanova/).

Reference for the paper

• Stringer, S.C. Webb, M.D., George, S.M., Pin, C. & Peck, M.W. (2005) Heterogeneity of times required for germination and outgrowth from single spores of nonproteolytic Clostridium botulinum. Applied and Environmental Microbiology, 71: 4998-5003

Further reading

• Barker, G.C., Malakar, P.K. & Peck, M.W. (2005) Germination and growth from spores: variability and uncertainty in the assessment of food borne hazards. International Journal of Food Microbiology, 100: 67-76.
• Barker, G.C., Malakar, P.K., Del Torre, M., Stecchini, M.L. & Peck, M.W. (2005) Probabilistic representation of the exposure of consumers to Clostridium botulinum neurotoxin in a minimally processed potato product. International Journal of Food Microbiology. 100, 345–357

Botulinum facts

• Most cases of foodborne botulism have been associated with home-preserved foods. The disease was first identified in blood sausage in the 1800s, and named after the Latin word for sausage, botulus. A current concern is the continued safe production of minimally processed chilled foods such as ready meals.
• Botulism might be rare, but it is the most severe foodborne illness –botulinum neurotoxin is a million times more potent with cyanide. In the UK 58 cases of botulism have been recorded since 1922, 19 of which were fatal.
• The mission of predictive microbiologists, such as the team at IFR, is to help regulators and industry ensure the disease remains rare, particularly as new foods and new processes are developed.

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