Purpose: This study tracked L. monocytogenes contamination patterns for six months in two meat processing facilities. Employee trainings, suggested mitigation strategies, and behavioral assessments were provided. Follow-up sampling was conducted to assess the impact of these control measures.
Methods: Sponge samples were collected monthly from environmental sites and products, and processed according to USDA-MLG protocol 8.07 with modifications. EcoRI ribotyping was used as the subtyping method for L. monocytogenes isolates. Assessments of employee knowledge and self-reported behaviors were analyzed via a Paired t-Test and a McNemar's Test, respectively. Suggested facility physical changes were implemented. Follow-up samples were collected on two occasions using identical testing methodology and subtyping.
Results: Statistical analyses identified persistent L. monocytogenes strains in Facilities 1 and 2. Employee knowledge assessment score means increased for both facilities post-training; Facility 2 knowledge increased significantly (P < 0.05). Facility 1 implemented physical facility improvements post-training, and significant behavior changes were reported. Follow-up sampling demonstrated that Listeria prevalence decreased significantly (P < 0.0001) although ribotype DUP-1042B persisted. Facility 2 reported one significant behavior change, did not immediately implement physical improvements, and Listeria prevalence remained at 44.1% for follow-up sampling 1. The facility’s lowest point prevalence (11.8%) followed implementation of physical improvements between follow-up samplings 1 and 2.
Significance: A combination of testing, molecular subtyping, employee trainings, and physical facility improvements may aid in mitigation of L. monocytogenes contamination. However, outcomes may vary by facility and persistent subtypes may withstand stringent control measures that are implemented.