Rapid Micro Rolls On

Increasing sample throughput is important during a contamination incident. One large poultry processor that routinely tested carcass rinses for Salmonella using rapid method assays noted an upward trend in positive results that it could not attribute to seasonality, according to DuPont. The plant examined its procedures to see if there was a contamination problem or whether its testing methods were faulty. The processor initially used cultures to monitor its interventions but could not wait five to seven days to get results.

With BAX’s DNA-based detection, the company could get results the next day and increased its weekly sample throughput by 25%. Within two months, the rate of positive Salmonella results fell from 18% to 5%, and soon thereafter to zero. DuPont said the fast turnaround of the results helped the company more quickly confirm the effectiveness of each change made in its process.

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DuPont Qualicon’s BAX system has 13 polymerase chain reaction (PCR) assays that target nine microbes. This is an image of results from 2009 using PCR with real-time detection showing clear positive or negative results for 96 tests in one batch.

Simplifying Procedures

Simplifying testing procedures to make them less prone to human error and to ensure quicker results are strategies also adopted by Applied Biosystems Inc., part of Life Technologies Corp. “We are looking for ways to process the sample after enrichment to get faster time to results,” said Brooke Schwartz, MBA, senior director of Food and Environmental Testing at Life Technologies.

Although she did not divulge information about upcoming products, she said “some exciting technology is in the pipeline. We are working on reducing time to results and increasing ease of use in our entire workflow.”

The company also uses a PCR-based technique with its MicroSEQ detection kits that run on the Applied Biosystems 7500 Pathogen Detection System. The company believes PCR is more specific than immunoassays, which are also used to detect pathogens. “PCR is more specific and has a faster time to result (than immunoassay),” said Manohar Furtado, PhD, vice president of research and development at Life Technologies.

Key to the company’s focus is the use of lyophilized beads during PCR. The reagents used in its MicroSEQ Listeria monocytogenes detection kit, for example, are lyophilized into pre-formatted assay beads that hold the active enzyme, the target-specific primer and probe set, and other reagents for “fast” PCR. Listeria monocytogenes bacteria grow slowly and are difficult to distinguish from other species of Listeria on agar. Dr. Furtado said the beads eliminate some of the potential human error or contamination, and the automated sample prep leads to faster results.

The assay process is closed, meaning that the tubes are closed until detection is complete, reducing contamination potential. Listeria testing with traditional culture-based methods can take up to five days, Dr. Furtado said. Older PCR methods that took 2.5 hours have been reduced to 45 minutes by automating workflow and using the beads. The company is also looking at multiple types of growth media to reduce the time to results.

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The food and beverage industries have increased their use of rapid microbiology testing over the last several years.

Tracing the Origin of Contamination

Recent food contamination outbreaks may suggest that the food supply is not safe, but that is not so, said J. Stan Bailey, PhD, director of scientific affairs at bioMérieux in Athens, Ga. “We are better now at identifying where the pathogen came from, and fewer people get sick,” he said. For example, the Peter Pan peanut butter outbreak was narrowed down to a particular brand at a particular plant. The Salmonella outbreak at Peanut Corporation of America in the summer of 2008 took longer, he said, because the outbreak wasn’t in a specific brand. Instead, it was a minor ingredient that went into hundreds of other products, including trail mix and other processed foods. The same was true of the melamine found in cat food. Now, government surveillance networks and tests more quickly track down the culprit. BioMérieux has an automated pathogen detection system called Vidas and an automated enumeration system for quality indicators called Tempo.