Reducing food recalls with rapid Salmonella detection

A rapid test developed by researchers from the Fraunhofer Institute for Cell Therapy and Immunology, Branch Bioanalytics and Bioprocesses can help detect Salmonella in food in eight hours. When it comes to detecting the presence of Salmonella in animal products, traditional microbiological techniques can take up to four days — this can be too long for food manufacturers, who need to distribute their products.

Along with German microbiology and food analysis laboratory Selektis, researchers from Fraunhofer have developed a rapid test that can determine whether food is contaminated with Salmonella in less than eight hours. Enriching bacteria is a time-consuming process that involves cultivating and propagating microbes, which are available in limited quantities, in a liquid culture medium overnight, so there is a high enough bacterial count for subsequent detection. This process can take 18 hours, with three further days needed for the selective enrichment and incubation of the salmonellae in liquid media, for the streaking of a bacterial culture on agar plates and for the serological test. Researchers have now reduced the time needed for the enrichment process from 18 hours to between four and six hours.

“We did this by creating a rapid culture with growth conditions optimised for salmonellae. By means of an innovative enrichment method, we are able to increase the concentration of the bacteria to such an extent that we can detect them using molecular biological methods after only a few hours. To do this, the DNA of the salmonellae is amplified and automatically detected, something we achieve by extracting the DNA of the salmonellae and amplifying them by molecular biological means to such an extent that they can be detected after a further 30 minutes. For the rapid test, we design the molecules that specifically detect the DNA of the salmonellae,” said Dr Harald Peter, Research Group Leader at Fraunhofer.

The automated system for sample preparation and pathogen detection could look like this. Image credit: Fraunhofer.

Researchers must obtain as high a concentration as possible of Salmonella DNA in a short time frame for the detection process. Researchers can then use fluorescent dyes to label the replicated DNA and detect it using capture modules. For this project, researchers developed a system that automatically performs all procedures that are done manually, such as cultivation, enrichment, molecular biological replication and detection. In the future, all necessary components will be integrated into a compact device; using molecular biological techniques, researchers will be able to skip certain DNA purification steps, thus simplifying the process of Salmonella detection.

The German Food Hygiene Act stipulates that a sample of 25 grams of meat must not contain a single Salmonella bacterium. Consequently, the new rapid test has to be capable of detecting a single bacterium within six to eight hours — that is, within an average working day. A further task is to distinguish the salmonellae from other microorganisms,” Dr Peter said.

Another advantage of the test is that it can also be applied to other food pathogens, by adapting the capture molecules to other organisms using a computer and gene databases.