When it comes to food safety, being able to detect pathogens in food production areas is crucial. Although swabbing machinery, hard surfaces and other environmental elements has served as a well established, state-of-the-art sampling method for this detection, it has several drawbacks, according to recently published research in the American Society for Microbiology’s Applied and Environmental Microbiology journal.

Issues talked to “. . . standardization, overall handling and long-term monitoring” led society to develop and evaluate a method that is as sensitive as environmental swabbing in addition to being easier to use, at a lower cost. The study found that using paper stickers to collect samples from surfaces like food processing plants wher antisepsis is required is “easier, and less expensive than swabbing, yet similarly sensitive.”

One of the authors said the porous structure of paper proved the ability to collect and accumulate bacterial contamination, which requires mechanical contact such as a hand, or splashed liquids. Investigators for the study, who specialize in monitoring cheese production, chose to target Listeria monocytogenes, a pathogen that commonly contaminates raw milk and other raw dairy products, including soft cheeses such as Brie, Camembert, and Feta. They used qPCR, a method of quantifying pathogen DNA samples to determine the numbers of these bacteria, as well as of Escherichia coli.

Food processing plant surfaces must be cleaned regularly, and unlike swabs, artificially contaminated stickers were able to provide a record of contamination that took place over at least two weeks, despite washing, flushing with water, or wiping with the alcohol-based disinfectant Mikrozid to simulate cleansing practices.

“Recovery [of DNA] from the stickers was rather variable, at around 30 percent, but did not distinctly decrease after 14 days of storage,” the study says. “This suggests the possibility of sampling over two weeks as well.”

The researchers placed stickers at multiple locations like light switches and door The “proof of concept experiment” showed both bacterial species were detected repeatedly from the stickers.

In contrast, the swabbing method is impractical on complex surfaces like door handles, light switches, and fomites, which are other objects likely to be contaminated with, and spread infectious organisms. Swabs do a poor job of taking up bacteria from dry surfaces, according to the report.

“In the food production facility, conventional swabbing as a standard method can only expose a momentary snapshot,” the investigators wrote. “For example, it is not possible to reconstruct information about yesterday’s status after cleansing has been performed. In addition, when moistened swabs or contact-plate sampling methods are used, they bring with them growth medium into a supposedly clean environment, making subsequent disinfection necessary.”

The investigators showed that plain paper stickers could not only trap bacterial pathogens and related DNA, but also dead, and viable but non-culturable pathogens, which also can pose a threat to public health.

As on author explained, a major advantage of stickers is in handling, as they are easy to distribute and to collect; Stickers can be directly placed into the DNA-extraction kit’s first protocol step, and investigators noted that they did not encounter any inhibition or loss of information during DNA-extraction, or qPCR.

By Kelsey M. Mackin