DNA amplification shows promise for food safety testing

UK-based Campden and Chorleywood Food Research (CCFRA) says the new PCR protocol was developed and validated for Enterobacteriaceae, Pseudomonas, Bacillus and Clostridium species.

Enterobacteriaceae are among the most pathogenic and most often encountered organisms in microbiology. Infection can cause intestinal problems, meningitis, bacillary dysentery, typhoid and foodpoisoning. Salmonella is one type of Enterobacteriaceae.

Tougher regulatory standards and the increased reporting of food contamination in restaurants, supermarkets and processing plants has pushed companies to put a higher priority on safety, shelf lifeand cleanliness. The trend has fueled the demand for more stringent testing and tracing of food products along the supply chain to the consumer.

PCR has become one of the top laboratory methods for microbacterial detection in the food industry as it can detect small samples of contamination by amplifying the amount of DNA, the genetic codethrough which technologists can determine what is present in the food product.

Chris Baylis, manager of Campden's micro methods research group, told FoodProductionDaily.com that the scientists involved in the project currently have no plans to commercialise the technology butwould be willing to work with those who want to use it.s

"If a commercial partner was interested we would be willing to discuss this further with a potential opportunity of developing this as a service,"​ he said. "At present weare busy developing our identification services using other technologies from traditional biochemical tests through to automated ribotyping and sequencing. The technology we developed would be ideallysuited to a microarray platform and this would be the next stage if we pursued this further."​

The research firm said its scientists had automated ribotyping for characterising microorganisms below the species level. The technique can be increasingly used for identification.

To complement the technology, scientists have the possibility of developing an identification system based on the capture of PCR-amplified DNA sequences onto DNA microarrays.

A microarray is a solid surface such as a microscope slide, onto which the amplified DNA is bonded. The microarrays can then be used to probe an unknown organism to see which of the DNA sequenceson the array are also present in the organism.

Microarray probes were designed for selected groups of bacteria, based on regions of the 16S ribosomal RNA. The firm then developed PCR protocols for the four species.

"Although observed hybridization did not always match that predicted by computer analysis of sequences, the research supported the belief that PCR/hybridization protocols will become apreferred technique for microbial identification,"​ the firm stated.

Baylis said food companies would be unlikely to operate the procedure themselves because of the capital cost associated with the equipment required and the skilled staff needed to run the test andinterpret the data.

"It would therefore be more suitable as a service that could be operated by an establishment such as ourselves and we would then be able to offer identifications at a competitive rate dueto the volume of tests being performed,"​ he said. "Furthermore, we would also be in a position to interpret the data and give advice to users of the service and provide assistancewith other aspects of microbiology, including the use of alternative techniques that would assist with pin-pointing sources of contamination and implementing hygiene strategies to resolve theseproblems."​

The firm currently does not offer the DNA probe hybridisation technology as a service. The research was done to provide proof it could be done.

However food companies have increasingly been using the established identification services at CCFRA, including PCR based tests, sequencing and ribotyping involving the RiboPrinter by DuPontQualicon, Baylis said.

Suzanne Jordan manages the identification services at CCFRA.