Prevalence and Molecular Diversity of Listeria monocytogenesin Retail Establishments

As our understanding of Listeria monocytogenestransmission in retail and deli operations is limited, we conducted a cross-sectional study of L. monocytogenescontamination patterns in 121 retail establishments, using testing of food and environmental samples and subtype analysis (ribotyping) of L. monocytogenesisolates. Seventy-three (60%) establishments had at least one sample that tested positive for L. monocytogenes; 5 (2.7%) of the 183 food and 151 (13.0%) of the 1,161 environmental samples tested positive for L. monocytogenes, including 125 (16.7%) and 26 (6.3%) of non–food contact and food contact surface samples, respectively. Thirty-two EcoRI ribotypes were identified among the 156 L. monocytogenesisolated. Twenty-seven establishments had two or more L. monocytogeneswith the same ribotype within a given establishment, including 9 establishments where isolates from 3 to 5 samples had the same ribotype. In 5 of 7 establishments where follow-up sampling was conducted 8 to 19 months after the initial sampling, isolates with the same ribotype were obtained in both samplings; persistence of a given strain was also confirmed by pulsed-field gel electrophoresis. Our data indicate that (i) L. monocytogenesis regularly found in some retail environments; (ii) L. monocytogenesstrains are often widely distributed in retail, indicating cross-contamination and dispersal; (iii) L. monocytogenescan persist in retail environments for more than 1 year; and (iv) a number of L. monocytogenessubtypes isolated at retail are common among human listeriosis cases. We also identified specific contamination patterns in retail establishments, providing critical information for the development of L. monocytogenescontrol strategies.