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Longitudinal study of Salmonella enterica, Escherichia coli O157:H7, and Listeria monocytogenes in a small and very small fresh meat processing plant environment




Orellana, Eva Danira Borjas, author
Bunning, Marisa, advisor
Nightingale, Kendra, committee member
Kendall, Patricia, committee member

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Small and very small fresh meat processing facilities have scarce resources to monitor foodborne pathogen contamination patterns and transmission dynamics in their premises. Environmental control of Salmonella enterica, Escherichia coli O157:H7, and Listeria monocytogenes, is important to prevent cross-contamination of meat products by pathogens that may persist in a facility. Although Listeria spp. are non-pathogenic, a high prevalence in a meat processing environment indicates failures in the cleaning and sanitation procedures. The purpose of this study was to conduct a six month longitudinal study to monitor Escherichia coli O157:H7, S. enterica, L. monocytogenes and other Listeria spp. contamination patterns, and to identify potential harborage sites in a small and very small fresh meat plant. Additionally, in order to gain insights about the facilities, manufacturing practices, and other relevant practices, managers from the two participating plants were asked to complete a questionnaire. Feedback of the study results was given to plant staff in a bilingual session, along with a basic training in food safety topics. Both plants were sampled during mid-shift operation on a monthly basis. Environmental site (n ≤ 54) and beef carcass composite samples were collected mid-shift. Samples collected included food contact surfaces (e.g., tables, scales, bins), and non-food contact surfaces (e.g., walls, drains, sinks). Overall, 1,979 environmental sponge samples were collected and microbiologically analyzed to detect and isolate S. enterica, E. coli O157:H7 and L. monocytogenes. Further characterization of the recovered pathogen isolates by molecular subtyping (e.g. PFGE, ribotyping) was performed to gain insight in contamination transmission within the facilities. S. enterica was isolated from 15 (4.5%) and 8 (2.4%) samples from Plant 1 and Plant 2, respectively. Characterization by PFGE using XbaI generated 6 different patterns in Plant 1, whereas all isolates from Plant 2 had the same pattern. S. enterica was recovered more than once from two sites in Plant 1, but only 2 isolates recovered from a drain in the slaughter area yielded the same PFGE pattern. E. coli O157:H7 was detected in 1.2% of samples in Plant 1; PFGE using XbaI generated 2 different patterns, and none was recurrently isolated from a single site. E. coli O157:H7 was not isolated from Plant 2. Over the course of the study, roughly 28% and 6% of the samples tested positive for Listeria spp. other than L. monocytogenes, in Plant 1 and 2, respectively. Listeria innocua was the predominant Listeria spp. in both plants. L. innocua allelic type AT-1 was recovered from 15% of samples collected across Plant 1, whereas in Plant 2, type AT-6 was found mostly contained in the slaughter area. L. monocytogenes was isolated from 17% of the samples from Plant 1 and 1.2% of samples from Plant 2. Roughly 97% (54/56) of L. monocytogenes isolates recovered from Plant 1 belonged to ribotype DUP-1042B, which was recovered up to five times from 15 different sampling sites across the facility; the remaining two isolates belonged to ribotype DUP-1057B. Noteworthy, ribotype DUP-1042B belongs to a major human outbreak-associated clonal group known as Epidemic Clone I, posing a high risk for meat product contamination in this facility. Conversely, in Plant 2, L. monocytogenes DUP-1030B was recovered from three samples and only one isolate belonged to DUP-1030A; no single site in Plant 2 repeatedly tested positive for L. monocytogenes. In light of the bacteriological results from this study, good manufacturing practices for the control of environmental contamination practiced by Plant 2 seem to be effective in the prevention of contamination spread and pathogen persistence; e.g. sanitizer dip stations at entry points, use of foam to clean equipment, use of quaternary ammonium compounds (QAC) or chlorine for sanitation of floors and other food contact surfaces, and QAC for sanitation of drains. Some high risk procedures practiced by the cleaning crew in Plant 1 may contribute to contamination spread; e.g., use of high pressure water for daily cleaning of drains, no sanitation step after cleaning drains, and lack of designated cleaning tools for drains. Although economic resources may be limited, microbiological monitoring of the plant environment is useful from a risk assessment standpoint. In this study, the prevalence of L. monocytogenes was high and widespread in Plant 1, and a predominant strain belonging to an Epidemic Clone group was elucidated. This information increases awareness and provides the plant management with valuable information for decision making, and motivates the implementation of new policies and targeted interventions in problematic areas. Our findings suggest that L. monocytogenes and L. innocua have higher prevalence than S. enterica and E. coli O157:H7 in the fresh meat processing plant environments. While L. monocytogenes may persistently contaminate the environment of fresh meat processing plants, E. coli O157:H7 and S. enterica contamination appears to be mostly sporadic.


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bilingual fact sheets
fresh meat
foodborne pathogens


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