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Listen to this siteMonday 17 October 2005
This project aims to explore the responses of the foodborne bacterium Salmonella typhimurium to stress encountered during commercial food processing or storage
Study Duration : December 1998 to December 2001
Contractor : University of Edinburgh
Salmonella and Campylobacter are major causes of foodborne disease in the UK. The link between contaminated poultry and infection in humans is well known. In order to cause infection in consumers, such organisms need to persist through the commercial processes used for food processing and storage.
Bacteria are known to be capable of adapting to many adverse conditions by inducing stress proteins, which minimise the harmful effects of the environment. The risk of infection is thought to depend not only on the number of potentially harmful bacteria present on food, but also their status and ability to recover from sub-lethal stresses encountered during food processing. To properly evaluate and reduce the overall risk to the consumer, it is important to dissect and assess the risk at each of the stages between the initiation of food processing through to consumption. The fact that bacteria can alter their protein composition in response to the environment or any stresses they encounter means that stress-specific proteins may exist within these cells. These proteins can be used as a quantitative marker of the number of harmful bacteria which exist on the foods, and what treatments or environments they have encountered. Such markers would reflect the stress history of the bacteria and the processing which they and the foodstuff have received.
The overall project aim is to explore the response of the foodborne bacterium, Salmonella typhimurium , to stress encountered during commercial food processing or storage. The project will focus on characterising the change in protein profile, which occurs following exposure to the sanitising agent hypochlorite and to incubation at refrigeration temperatures, since these commonly feature during poultry processing. The project also aims to determine whether stress proteins could be identified with suitable characteristics, so that they may have value as indicators of the stress history of the organism. If such markers are found, the project intends to determine their level of sensitivity.
The approaches consist of:
The purpose of this project was to explore the response of the foodborne bacterium, Salmonella typhimurium , to stress encountered during commercial food processing or storage, including refrigeration and the sanitising agent hypochlorite.
The findings indicated that incubation at low temperatures had a major effect on the proteins which were made in the
Salmonella
cell. At low temperatures (4 and 10
C), production of most proteins declined and even appeared to cease initially for exponentially growing cells but, simultaneously, production of a small number of stress proteins appeared to occur. With slow growing cells, a similar response was observed in the early stages following incubation at low temperatures. The time scale of the response was slower and the normal pattern of protein production (at higher temperatures) did not return. Instead, protein production declined until production of only stress proteins was observed.
The hypochlorite response was quite different, as most proteins continued to be made in the cell, with only a few showing increased synthesis. No highly induced, uniquely stress-specific proteins could be identified and development of a suitable assay for this stress was considered not to be possible based on this approach.
From the �strained� protein profile, it could be seen that some of the stress proteins accumulated during storage at both low temperatures, and in both fast and slow growing cells. Following identification, a smaller number of the proteins were produced artificially and these were used to raise antibodies for assay development. The antibodies were purified and tested for their binding specificity. When cells from 37
C and 10
C were compared, a higher signal was detected from the chilled cells and this signal was detectable with as few as 100,000 bacteria.
The research has provided information on how foodborne bacteria may persist during industrial food processing and has revealed involvement of unknown protein components. However no suitable stress-specific marker proteins were found for cells exposed to hypochlorite. In contrast, evidence was found that a suitable marker is available for development of an assay for cells which have been refrigerated. Such an assay may be beneficial for analysing the risks associated with different stages in the chain of infection from animals to man; for identifying points of hygiene failure where improvements should be made, or of use with other foodborne bacteria such as Campylobacter .
Final report is available from the Agency's Information centre.
To obtain a copy, please contact the Enquiry Desk, Information Services, Food Standards Agency (tel: 020 7276 8181/8182 or email:
infocentre@foodstandards.gsi.gov.uk
).
Contact
: For any enquiries concerning this research project, please contact the relevant Programme contact or email:
science@foodstandards.gsi.gov.uk
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