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A faster way to detect Listeria: New method takes 8 hours instead of 24 or more

A new study demonstrates the capability of a streamlined workflow to detect low-level presence of Listeria monocytogenes in food samples within 8 hours. The study results were in Microbiology Spectrum.

"Using the current laboratory methods, it takes 24 to 72 hours to identify food samples contaminated with a low level of Listeria monocytogenes," said lead study author Min Lin, Ph.D., a research scientist with the Canadian Food Inspection Agency. "We conducted this study to develop a streamlined sample-to-answer procedure to shorten the detection of L. monocytogenes in food samples."

L. monocytogenes, a rod-shaped Gram-positive bacterium widely distributed in nature, can contaminate foods and has a high mortality rate of 20–30%. Rapid and reliable identification of foods and food-processing environments contaminated with L. monocytogenes is a crucial step in implementing effective intervention strategies to ensure food safety and limit the transmission of foodborne pathogens to humans.

In the new study, researchers designed a sample-to-answer detection workflow by integrating various methods such as culture enrichment, filtration-based sample preprocessing, magnetic separation of target bacteria and real-time polymerase chain reaction into the detection workflow.

They evaluated the workflow using ground beef samples artificially contaminated with 1 to 5 cells of L. monocytogenes in 25-gram analytical units. The workflow allowed the detection of L. monocytogenes within 8 hours in a 25-gram sample unit containing a cell count as low as 2 L. monocytogenes cells.

"Once the streamlined procedure is evaluated thoroughly and implemented in food microbiology testing laboratories, it will significantly reduce the turnaround time for L. monocytogenes testing in food samples," Lin said. "Future research will focus on evaluation of the described workflow for the detection of various L. monocytogenes strains in various food matrices, especially in naturally contaminated foods."

Lin said hopefully the study will stimulate the development of a fully automated system that is capable of completing all the steps in the workflow with little manual operation.