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E. coli 'hunter' test designed to stop food contamination

By Jane Byrne , 13-Apr-2011
Last updated on 13-Apr-2011 at 14:53 GMT

A new test method which is said to hunt out bacteria before they contaminate food could ensure greater control for food manufacturers against pathogens such as E.coli and also speed up the time to market for packaged foods.

Canadian researchers, writing in the journal Angewandte Chemie International Edition, show how their fluorescent test system – DNAzymes – designed to track the DNA trails of pathogens does not require the time consuming steps and specialized equipment typically used in standard microbial tests.

"Current methods of foodborne bacterial detection take time. The five days it takes to detect listeria, for example, can translate into an outbreak that costs lives.

We have developed a universal test that uses less complex procedures but still generates precise and accurate results," said lead researcher, biochemist Yingfu Li.

Bacteria have their own spoor, leaving behind DNA trails of bacterial 'droppings'. So Li explained that, based on this fact, his team developed a testing method that works by tracking these metabolic by-products with molecular beacons that light up when they detect the DNA sequence left behind.

He said the DNAzymes method can be used to set up a simple ‘mix-and-read’ bacterial detection assay.

"More importantly, we have demonstrated that our method has the capability to detect a single live cell,” said the authors, who stressed that the ability to to do so is a hallmark of a method to detect food-borne pathogens.

Furthermore, the Canadian researchers report that although their method was demonstrated using a nonpathogenic strain of E. coli, it can “easily be implemented for pathogenic bacteria and viruses.”

They added that while the demonstrated assay used fluorescence as the reporting mechanism, the same DNAzyme probe could be used for the design of a colorimetric assay using a rolling circle amplification/organic dye strategy.

USDA testing call

There have been notable outbreaks of foodborne illnesses arising out of E.coli contamination of foods such as beef, spinach and dough in the US in recent years.

Last week saw the US Department of Agriculture (USDA) claim that 44 of the most serious food recalls in the US from 2007 to 2009 could have been prevented if the agency had had a ‘test and hold’ procedure in place for meat and poultry products during that period.

In light of this, the department’s Food Safety and Inspection Service, which inspects “billions of pounds of meat, poultry and processed egg products annually” has proposed that companies should hold meat and poultry products until inspectors have received foodborne pathogen test results, in an effort to reduce illness.

The American Meat Institute, which represents most of the meat processing sector in the US, has welcomed the proposal.

Source: Angewandte Chemie International Edition
Published online ahead of print: DOI: 10.1002/anie.201100477
Title: Fluorogenic DNAzyme Probes as Bacterial Indicators
Authors: M. Monsur Ali, S. D. Aguirre, Dr. H. Lazim, Prof. Dr. Yingfu Li

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