P-067. A Longitudinal Study on Listeria monocytogenes Contamination Patterns in Small and Very Small Ready-To-Eat Meat Processing Plants

S. K. Williams1, S. Roof2, E. A. Boyle3, H. Thippareddi4, D. Burson4, K. K. Nightingale1, M. Wiedmann2, J. A. Scanga1, J. N. Sofos1;
1Colorado State Univ., Fort Collins, CO, 2Cornell Univ., Ithaca, NY, 3Kansas State Univ., Manhattan, KS, 4Univ. of Nebraska, Lincoln, NE.

Listeria monocytogenes is a foodborne pathogen that can cause listeriosis, a serious invasive disease in humans. This pathogen represents a significant challenge for the ready-to-eat (RTE) food industry due to its common isolation from virtually all environments along the food chain. A longitudinal study was conducted to track contamination patterns of L. monocytogenes in six small or very small RTE meat processing plants in Colorado, Kansas, and Nebraska. A total of 560 environmental sponge samples were collected from non-food contact surfaces (i.e., drains, floors, sinks, door handles, cart wheels, and equipment surfaces) over five visits to each plant. Samples were analyzed following a modified version of the U. S. Food Safety and Inspection Service procedure for the Listeria monocytogenes BAX® screening test. Overall, L. monocytogenes was isolated from 32 (5.7%) environmental samples and the prevalence of this pathogen ranged from 0 to 11.4% across different plants. Five sample sites tested positive for L. monocytogenes on more than one occasion. All L. monocytogenes isolates from these five sampling sites were characterized by multiplex PCR to group isolates into molecular subtypes representing serotypes responsible for majority of human disease (1/2a, 1/2b, 1/2c, and 4b). Two raw material processing sampling sites from two different plants were colonized by the same molecular serotype (1/2b) over multiple samplings. Listeria spp. other than L. monocytogenes were isolated from 11.6% of samples overall, and the prevalence of Listeria spp. ranged from 2.1 to 21.9% within different plants. Partial sigB sequencing showed Listeria spp. isolated from the RTE meat processing plants studied here predominantly included L. innocua and L. welshimeri. Interestingly, atypical hemolytic L. innocua were also isolated from four samples collected during a single sampling at one plant. Our findings suggest that L. monocytogenes may persistently colonize RTE meat processing plant environments and highlight the need for stringent sanitation controls to eliminate niches persistently contaminated by this pathogen.