Paper stickers demonstrate better alternative for testing food than swabs

Materials World magazine
1 Jul 2019

Paper stickers prove to be more effective than swabs for monitoring pathogens in food production. Shardell Joseph reports.

When collecting pathogens on surfaces where antisepsis is required, research suggests that paper stickers are easier, less expensive, and just as sensitive as swabbing. According to the study A novel method for sampling and long-term monitoring of microbes using stickers of plain paper, published in the American Society for Microbiology’s Applied and Environmental Microbiology journal, the porous nature of paper gives it the capacity to collect and accumulate bacterial contamination.

The study acknowledges the behaviour of the bacterium, Listeria monocytogenes, and its propensity to enter food production indirectly through surfaces such as door handles and switches. This pathogen frequently infects raw milk and other raw dairy items, including some varieties of soft cheeses.

The researchers sampled a system they described as having the highest sensitivity and ability to monitor over long periods of time, overall proving to be cost-effective and reasonably convenient to handle.

Testing the paper stickers for their suitability to uptake and release Listeria monocytogenes, the researchers used quantitative PCR (qPCR), to measure DNA samples and identify the varieties of the bacteria to test their exposed, non-sticky paper side over 14 days. They then put the stickers in numerous areas likely to encounter hand contact, such as light switches and door handles, for seven days. The bacteria was found consistently on these sticker labels.

Despite cleaning with an alcohol-based disinfectant, or flushing with water to imitate cleaning practices, the synthetically polluted stickers collected a record contamination level over a minimum of two weeks. This is seen to be a huge advantage over conventional swabbing, as surfaces in food processing plants need to be cleaned routinely.

‘Recovery [of DNA] from the stickers was rather variable, at around 30%, but did not distinctly decrease after 14 days of storage,’ the report stated. ‘This suggests the possibility of sampling over two weeks as well.’

Swabbing machinery, as well as hard surfaces and other environmental elements, is a well established method for pathogen detection. Yet, according to The University of Veterinary Medication researchers in Austria, it has several drawbacks in respect of yield, standardisation, overall handling and long-term monitoring.

In a report made by investigators, included in the study, swabbing is unwise on intricate surface areas, such as door handles, light switches, and other fomites – objects highly likely to be polluted – and spread transmittable organisms. Swabs are also ineffective for collecting germs from dry surface areas.

‘In the food production centre, traditional swabbing as a basic approach can just expose a temporary picture,’ the investigators said. ‘For instance, it is not possible to rebuild details about the other day’s status after cleaning has been carried out.

‘In addition, when dampened swabs or contact-plate sampling approaches are utilised, they bring with them development medium into an allegedly tidy environment, making subsequent disinfection needed.’

The investigators explained how the paper stickers have potential to trap dead and non-viable cultural pathogens as well as bacterial pathogens and related DNA, which can also pose a threat to public health.

‘A major advantage of stickers is in handling – they are easy to distribute and to collect,’ said The University of Veterinary Medicine, Department for Farm Animal and Public Health in Veterinary Medicine Technical Assistant, Martin Bobal. ‘We put the stickers directly into the DNA-extraction kit’s first protocol step. We did not encounter any inhibition or loss of information during DNA-extraction, nor during qPCR.’