Source:  Tom Johnston, MEATINGPLACE.COM, 4/20/10

Incoming raw poultry is the primary source of Listeria monocytogenes contamination in chicken cooking plants, according to a 21-month study conducted by USDA's Agricultural Research Service and the University of Georgia and reported in the Journal of Food Protection.

Researchers conducted the study in a new plant before and after operations began, allowing them to track sources of contamination including employees, incoming fresh air, raw meat and the surrounding environment.

Potential sources were tested by taking samples of soil and water around and near the plant's exterior, and by testing heavily traveled floor surfaces after shift changes. Researchers also collected and tested samples from incoming air from air vent filters and from monthly swabs of incoming raw meat. The plant was free of listeria when first built; floor drains were then sampled almost monthly to determine when the facility would become colonized with the pathogen.

Four months after operations began, listeria was detected in floor drains, suggesting the organism had been introduced by an outside source. None of the bacteria was detected from any floor samples in the plants entryways, locker room or cafeteria or from air vent filters. Incoming raw poultry meat was the only source consistently found to be positive for listeria, the study concluded.

The scientists said quality assurance in the test plant was "exceptional" and included an extensive, proactive sampling plan.

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