Fraunhofer researchers are helping to develop a test to detect Salmonella in less than eight hours.

A team from the Fraunhofer Institute for Cell Therapy and Immunology, Branch Bioanalytics and Bioprocesses are working with the German microbiology and food analysis laboratory Selektis GmbH as part of a ProFIT project running from 2018 to 2020.

Core technology of the detection system is DNA-based amplification. Project partners have reduced the enrichment process from 18 hours to between four and six hours.

The user knows if a sample is positive for Salmonella as there is a yes or no answer without quantification on a digital display with a limit of detection in accordance with ISO 6579. It’s compatible for all food samples and could be adapted to environmental samples.

Timely enrichment
Traditional microbiological techniques can take up to four days, which is a problem for some food manufacturers who don’t want to wait that long for results before shipping goods. If a problem is then found the company may have to make a costly product recall.

Enrichment involves cultivating and propagating microbes, which are available only in limited quantities, in a liquid culture medium overnight, so there is a sufficiently high bacterial count for detection. This process lasts about 18 hours, with three days needed for the selective enrichment and incubation of the salmonellae in additional liquid media, for streaking of a bacterial culture on agar plates, and for the serological test.

It is important to get a high concentration of Salmonella DNA in a short timeframe for sensitive detection. The researchers use fluorescent dyes to label the replicated DNA and detect it using capture molecules. Although molecular biological detection techniques are already in laboratories, they are rarely used in fully automated processes and not in food diagnostics.

Dr. Harald Peter said they have created a rapid culture with growth conditions optimized for Salmonella.

“By means of an innovative, optimized 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,” he said.

“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.”

Role of automation
Peter and his team plan to develop a system that automatically performs procedures that are done manually, such as cultivation, enrichment, molecular biological replication and detection.

Currently five samples can be tested at once but this could be adapted to 100. The test is based on viable cells only.

All components will be integrated in a compact device. Using special molecular biological techniques, researchers at Fraunhofer IZI-BB can skip certain DNA purification steps to simplify and speed up the process.

The focus is on strains relevant for food monitoring but the assay can be modified to other strains and species if capture molecules are adapted to other organisms using a computer and gene databases.

“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,” said Peter.

Business promotion banks for the federal states of Brandenburg and Berlin are sponsoring the project with funding from the European Regional Development Fund (ERDF).

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