Clostridium spores subject of IFR research

Clostridia bacteria survive in the environment as resilient, heat-resistant spores. They can be killed by heat so canned foods undergo a treatment of 121 degrees for three minutes.

IFR studied how spores of Clostridium sporogenes germinate, these bacteria are similar to those that cause botulism.

Clostridium botulism outbreaks are rare but to maintain food safety as much as possible needs to be understood about how these bacteria survive and grow, said the scientists.

Research aim​

Professor Mike Peck told FoodQualityNews the research was part of ongoing work by his group.

“There are two areas – the strategic fundamental work which is understanding the biology of the bacteria. Also, the strategic applied work with regulators and industry to ensure food safety. This is an example of the work into the fundamental biology of the bacterium,” ​he said.

“In order to cause foodborne botulism the organism has to grow and multiply and form the toxin in food. The botulinum toxin is the most potent known to man and is responsible for botulism​.

“In most foods C. botulinum is present as spores, like seeds of a plant, and resistant to environmental challenges. ​

“We were keen on understanding the process of how a spore, which is itself not dangerous (since no toxin), becomes a cell which is dangerous (since it forms toxin). Spores germinate and cells grow and make toxin and we can get botulism.”​

Scientists at IFR, which is funded by the Biotechnology and Biological Sciences Research Council, uncovered the genetic controls of spore germination in these bacteria.

SEM for the full picture​

Peck said the research had changed his impression of what happens during germination.

“In the past people had taken sections but with SEM you get the whole picture. It has helped us understand more spore germination and how the cells how they emerge from the exosporium​,” he said.

“Botulism is a rare disease but it is deadly and costly for human health and industry. There was a recent outbreak in Scotland in 2011 which involved three children from korma source in a jar. In April 2015 there was an outbreak in Ohio, in the USA involving canned potatoes.​

“We need to apply safe processes that we have identified for foods correctly and for milder processes we need to understand more about the bacteria.” ​

Dr Jason Brunt worked with microscopist Kathryn Cross to produce images of the stages spores go through during germination.

They examined Clostridium sporogenes, a close relative of Clostridium botulinum.

Images showed the spores have an outer covering, called an exosporium, with an aperture at one end.

Closer examination revealed this aperture aligned with a spot on the spore where it ruptures during germination, and the newly formed cell emerges through these holes.

This suggests the spores have polarity that aligns the structures correctly, said IFR.

However, the cell does not always exit immediately, with septated cells observed emerging through the exosporium.

Electron microscopy was used to visualise changes in spore structures during germination, emergence and outgrowth.

Despite extensive investigations on spore germination, coat structure, and clostridial cell growth from spores there is a relative lack of information regarding the cell's exit from its protective coats, said researchers.

Source: Food Microbiology Volume 51, October 2015, Pages 45–50

Online, ahead of print: 10.1016/j.fm.2015.04.013​

“Apertures in the Clostridium sporogenes spore coat and exosporium align to facilitate emergence of the vegetative cell”​

Authors: Jason Brunt, Kathryn L. Cross, Michael W. Peck