Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2012
Publication Date: 7/1/2012
Citation: Berrang, M.E., Frank, J.F. 2012. Generation of airborne listeria from floor drains. Journal of Food Protection. 75(7):1328-1331. Interpretive Summary: Listeria monocytogenes is a human pathogen capable of high mortality that has been related to poultry meat products. This organism generally can be found contaminating the environment inside poultry processing plants. Because everything in a poultry plant gets washed with running water and all the water finds its way to a floor drain, one site that often harbors Listeria are the floor drains. It is unclear if or how Listeria can travel from a floor drain to product. The objective of this study was to determine if an accidental discharge of a water hose into a contaminated floor drain could result in airborne transfer of live Listeria cells to other surfaces. We used a two second spray into an experimental model drain systems that had been previously inoculated with Listeria innocua, a non-virulent surrogate for L. monocytogenes suitable for use in aerosol studies. Using open Petri plates filled with Listeria specific growth media and air sampling machines, we were able to detect airborne Listeria within the experimental rooms. Listeria was detected settling out of the air as far away as 4.0 m (13 ft) on the floors and even 2.4 m (8 ft) high on the walls. Poultry processors will use this information to guide sanitation standard operating procedures relative to avoiding inadvertent hose spray into floor drains. Researchers will find this information critical as they design and test intervention strategies to prevent the escape of live Listeria from contaminated sites during poultry plant wash down.
Technical Abstract: Listeria monocytogenes can colonize floor drains in poultry processing and further processing facilities remaining even after cleaning and disinfection. Therefore, during wash down, workers exercise caution to prevent escape and transfer of drain microflora to food contact surfaces. The objective of this study was to examine the extent to which an inadvertent water spray into a colonized floor drain can cause the spread of airborne Listeria. L. innocua was used to inoculate a polyvinyl chloride (PVC) model floor drain resulting in approximately 108 cells per mL of phosphate buffered saline (PBS) and 104 attached cells per cm2 inner surface. Each model drain was subjected to a 2 second spray of tap water at 68.9 kPa from a distance of one meter. Drains were sprayed while filled and again after emptying. Airborne cells were collected by using sedimentation plates containing modified oxford (MOX) agar which were placed on the floor and walls of a contained room at incremental horizontal and vertical distances of 0.6, 1.2, 2.4 or 4.0 m from the drain. Sedimentation plates were exposed for 10 min. A mechanical sampler was used to also collect air by impaction on the surface of MOX agar to determine the number of cells per liter of air. The experiment was conducted in triplicate rooms for each of four replications. L. innocua was detected on sedimentation plates on the floor as far as 4.0 m from the drain and on walls as high as 2.4 m above the floor and 4 m from the drain. A 2 second accidental spray with a water hose into a contaminated area can cause airborne spread of Listeria resulting in the potential for cross contamination of food contact surfaces, equipment and exposed product.