Scientists from the US Department of Agriculture (USDA) said the findings would help poultry processing facilities improve their sanitation methods to reduce cross contamination.
The 21-month study conducted by the USDA’s Agricultural Research Service (ARS) was able to accurately track sources of LM contamination by testing a brand new commercial facility both before and after processing began.
Potential sources of contamination
LM is a bacterial human pathogen that is found ready-to-eat processed meat and poultry products, as well as in fully cooked meats. Given its prevalence in the environment, potential sources of contamination were employees, incoming fresh air, raw meat and the surrounding location, said the ARS research team lead by Mark Berrang.
“This finding allows the processor to recognize the potential for LM being in the raw product, the potential for such LM to colonise a plant and become long term resident in floor drains - and therefore, a processor can take appropriate steps to contain such contamination,” Berrang told FoodProductionDaily.com.
The team monitored all potential LM sources by taking samples of soil and water around the site exterior. Samples were also collected from incoming air from air vents, floors with heavy foot traffic following shift changes. Swabs were also taken from monthly samples of incoming meat.
Incoming raw poultry
When the plant was built ARS researchers established it was free of LM. Monthly testing of floor drains subsequently found that colonisation of the site by the bacteria occurred after four months. The team concluded this indicated the bug had been introduced by an external source.
“No L. monocytogenes was recovered from any floor samples in the plant entryways, locker room or cafeteria,” said the ARS. “Likewise, the organism was not detected on air vent filters during the survey. The only tested source found to be consistently positive for L. monocytogenes was incoming raw poultry meat.”
The group characterised quality assurance at the test plant as “exceptional” and included an “extensive proactive sampling plan to assure food safety”.
Berrang said: “All the product in the plant tested was fully cooked and temperature adequate to kill LM was confirmed through testing - so no consumer was in any danger at any time.”
The UK Food Standards Agency backed the need for processor vigilance in relation to the foodborne bacteria.
“Listeria may be present in a wide range of raw foodstuffs entering food processing plants,” said an agency spokesman. “It is important that manufacturers take this into account in their food safety management systems and take appropriate steps to address this source. Regular monitoring of the factory environment, equipment and surfaces for Listeria contamination is important so that environmental contamination is kept under control to avoid food contamination.”