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Neogen develops Listeria test with no enrichment

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By Joe Whitworth+

26-Jul-2017
Last updated on 26-Jul-2017 at 12:26 GMT2017-07-26T12:26:58Z

Neogen's Listeria Right Now test kit
Neogen's Listeria Right Now test kit

Neogen Corporation has launched a test that detects Listeria in environmental samples without the need for enrichment.

Listeria Right Now, which took three years to develop, can detect all species of Listeria in less than 60 minutes through their ribosomal RNA (rRNA).

Neogen said it removes the enrichment step enabling actionable results in one hour so corrective actions such as improving sanitation efforts or processes can be taken.

Making the pathogen detectable

The process starts with an environmental sample to capture any Listeria. The swab is placed in a tube that contains a lysis buffer that breaks up any bacteria present and releases its rRNA.

If Listeria is in the sample, the test's reagents will amplify thousands of copies of its rRNA - and make the pathogen detectable.

Gerry Broski, senior director of food safety marketing, said the base technology is isothermal amplification of rRNA. 

'Changes everything'

Ed Bradley, Neogen's VP of food safety, said it ‘changes everything’ about testing the environment for Listeria.

Contamination of Listeria in the environment can now be determined, and cleaned as necessary, before food production begins and the quality and safety of a food product is compromised,” he said.

“Using Listeria Right Now also means that companies no longer have to grow potentially dangerous cultures in their facilities during the testing process, nor store test cultures for potential follow-up testing."

“Ribosomal RNA was chosen as the target since it is present in thousands to tens of thousands of copies in Listeria spp. cells, thus making this assay very sensitive. Through a reverse transcriptase reaction, rRNA is converted to DNA. Isothermal amplification enables us to replicate the nucleic acid very quickly, and without enrichment.”

If Listeria is present, a template equipped with a molecular beacon binds the target nucleic acid and results in fluorescence. The fluorescence increases during the amplification process and is detected by the Neogen ANSR instrument.

Negative samples will not produce fluorescence. An internal positive control is included in each reaction to ensure the amplification reaction conditions are suitable.

The test is under review for AOAC Performance Tested certification with approval expected later this year.

When asked if the test would be expanded to other pathogens or food samples, Neogen would only say it will continue to invest further development in products to help customers address requirements to produce safe food.

Enrichment-based methods

Typically environmental surfaces are swabbed according to a recommended protocol or sSOP and then the swabs or sponges are processed using an enrichment-based testing method.

“These methods require 24-48 hour enrichments followed by analysis via traditional plating methods, PCR, or real-time PCR, or through one of the newer rapid molecular methods,” said Broski.

“The main drawback with these methods is the long enrichment time. For companies that have to sample and hold product while awaiting test results, this is a bottleneck and is costly. Total time from a sample to result up to this point has been measured in days.

“While cell viability is an issue regrading lethality, the detection of Listeria on a surface in a food plant is a cause of concern and should be addressed through good sanitary practices or corrective actions.” 

NSF enlisted for validation study

The system was validated by NSF International to detect low levels of Listeria in environmental samples.

The testing laboratory found that Listeria Right Now was as sensitive as enrichment based culture reference methods for detecting Listeria spp. on environmental surfaces. 

Limit of Detection is 4 CFU per swab with 95% confidence.

When asked about Lab M’s role – a firm it bought in 2015 - following this test which removes the need to enrich samples and the NeoSeek genomic testing services which removes culture media bias, Neogen said the products and technologies it has can be viewed as complimentary.

“Lab M has been integrated into the Neogen family of products and just like with other technologies we are looking to leverage their capabilities into new or existing products or services,” said the firm. 

“Lab M chromogenic media, µprep dry bags and unique media offerings are already well received and we continue to look for opportunities to address the needs of the food processing and production industry.”

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