Growth of Listeria monocytogenes Inoculated in Waste Fluids Collected from a Slaughterhouse

Cells of Listeria monocytogenes Scott A were artificially inoculated (26-378 CFU/ml) in waste fluids collected from a lamb slaughtering operation, and their growth was determined at 8 and 35°C. Samples tested included residual fluid from carcass rinsing (after hide and offal removal); a mixture of waste fluids from the floor (collected during the entire slaughtering and washing process); and a standard floor drain sample (drawn from the floor drain 5 min after clean-up was complete). Growth of L. monocytogenes within 24 h of incubation of the various waste fluids was more rapid at 35 (1-4 logs) than at 8°C (0.5-2 logs). Average generation times of L. monocytogenes growth at 8°C were in the range of 12.3 to 35.1 h, depending on waste fluid, while at 35°C generation times were in the range of 1.1-6.4 h. Therefore, waste fluids in slaughterhouse facilities can support growth of L. monocytogenes , which may then be introduced on carcasses and retail meat cuts. Thus, slaughterhouse temperatures should be as low as possible and cleaning and sanitation should be frequent in order to minimize carcass and retail meat contamination with the pathogen.