Purpose: This study aimed to 1) conduct longitudinal sampling for Listeria monocytogenes, Salmonella enterica, and Escherichia coli O157:H7 in four ready-to-eat or fresh meat production facilities, 2) perform molecular subtyping and statistical analyses to elucidate transmission patterns and sites of persistence, 3) provide in-plant trainings and suggested interventions, and 4) conduct follow-up sampling to determine training and intervention effectiveness.
Methods: Briefly, sponge samples of environmental sites, food contact surfaces, and finished products were collected monthly for six months and processed to isolate pathogens according to modified USDA-MLG protocols 4.05, 5.05, and 8.07; the same methodology was used for follow-up sampling. Isolates were characterized by molecular subtyping and data were analyzed using binomial statistical tests to identify persistent subtypes and harborage sites. Trainings were held after the initial six-month sampling period and covered facts on foodborne pathogens and persistence, facility-specific results, and suggested interventions. A paired t-test was used to compare pre- and post-training exam scores to assess participant knowledge changes.
Results: EcoRI ribotyping statistical analysis revealed persistent ribotypes and harborage sites for L. monocytogenes in Facility A (DUP-1052A, 116-239-S-2; two sites), Facility B (DUP-1062B, DUP-1062E, DUP-1052E; one site), and Facility C (DUP-1042B; six sites). No persistent XbaI PFGE pulsotypes of S. enterica or E. coli O157:H7 were statistically identified. Exam score means significantly increased (P < 0.05) from pre- to post-training for three facilities. Among sites that were positive at least once, point prevalence for L. monocytogenes on the midshift follow-up sampling date was less than the six-month mean prevalence for two of the three facilities sampled.
Significance: These data suggest that particular L. monocytogenes subtypes may persist in the meat processing environment while subtypes of S. enterica and E. coli O157:H7 are likely transient. Furthermore, highly targeted interventions and training may be necessary to achieve mitigation of L. monocytogenes once persistence is established.