The world is awash with new rapid testing technology that is enhancing food quality and safety knowledge for the global food industry and consumers alike.
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Explore This IssueDecember/January 2019
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Identifying Listeria Patterns
In July 2018, Rheonix Inc., Ithaca, N.Y., launched its Listeria PatternAlert assay, which the company calls a breakthrough method for rapidly identifying molecular patterns from Listeria strains.
“The method is designed to assist food producers in identifying harborage sites for persistent Listeria and in tracing back sources of contamination, says Brooke Schwartz, MBA, vice president for strategy and marketing, Rheonix.
According to Schwartz, feedback about the assay from food manufacturers and testing labs has been enthusiastic.
“We are supporting this technology because of the potential value that it would have for our clients,” says Timothy Freier, PhD, vice president of scientific affairs and microbiology, Mérieux NutriSciences, Chicago, Ill., Rheonix’s beta testing partner for the Listeria PatternAlert assay. “The ability to have Listeria tracking information within hours of a presumptive positive result would greatly enhance environmental contamination investigations, allowing manufacturers to find and fix issues before their product is impacted, saving costs and benefiting public health.”
Current strain typing methods take up to two weeks to complete and require an isolate in pure culture, Schwartz points out. “The Listeria PatternAlert assay, which is performed using the fully automated Rheonix Encompass Optimum workstation, enables users to detect molecular patterns in just six hours directly from a positive enriched sample, without the need for an isolate,” she relates. “Each result can be matched against a user’s specific PatternAlert database to identify their pattern matches across locations and time.”
Persistent Listeria strains that find a harborage site in a food facility can significantly increase the risk of broader contamination, and are a target of increasing regulatory scrutiny, Schwartz notes.
Schwartz explains that because the goal of the assay is to identify recurring patterns in a company’s facilities, its greatest value lies in the ability to match new patterns from a given user (i.e. company) to previously observed patterns. “However, even new users can see value in testing an initial group of samples, determining whether presumptive positives samples from a single day or week of testing reflect the same or different patterns,” she emphasizes. “The value increases as more samples are tested over time and across the user’s locations.”
According to Morgan Wallace, PhD, Rheonix’s scientific director for applied markets, the Listeria PatternAlert assay detects the presence or absence of independently occurring genetic targets that can sort Listeria into thousands of potential patterns. “Each pattern generated by the assay encompasses a group of strains and may include multiple species of Listeria,” he explains. “Our approach is to provide information directly from enriched samples that can help users identify recurring strains or populations. The discriminatory power of the PatternAlert assay was carefully calibrated to enable users to make informed decisions based on molecular patterns, without the assay providing a strain level characterization equivalent to whole genome sequencing (WGS) or pulsed-field gel electrophoresis.”
The assay, in combination with the PatternAlert analytical software, addresses the questions:
- Where and when have I seen this pattern before?
- Do I have a potential harborage site?
- Am I seeing the same pattern over time or across facilities?
WGS has a much finer level of discrimination, Dr. Wallace points out. With the ability to discriminate down to the single nucleotide level, WGS enables users to determine whether two strains are identical or very closely related to each other,” he says. “This level of differentiation may be desired when determining whether a specific strain is related to an outbreak or widespread food contamination.”