Public health importance and antibiotic resistance patterns of listeria species in food and food processing environments in selected districts of Zambia.

Awareness of food safety risks has increased, given the occurrence and intensity with which zoonotic diseases are reported. Due to the widespread distribution of food products, controlling foodborne pathogens has become increasingly relevant worldwide. Consequently, this present study aimed to evaluate public health importance and antibiotic resistance patterns of Listeria species in selected Districts of Zambia across foods and food processing environments.
654 food and environmental samples were collected from poultry abattoirs n=150, beef abattoirs n=250, fish plants n=150, RTE deli meats n=52, lettuce n=52, and environmental samples n=80. Samples were collected randomly, using a cross-sectional study design from March 2020 to August 2021. Samples were first imperiled to pre-enrichment in half-strength Fraser broth, followed by enrichment in full-strength Fraser broth, and subsequent plating on Listeria agar. Listeria growth characteristics were identified based on their morphological and biochemical reactions. Quantitative survey data were analyzed using STATA Version 15.0 software and WHONET. Further, we used molecular detection to determine genes conferring resistance and genomic relatedness of Listeria species. Custom pipeline was used for sequence assembly and analysis.
Of the 654 samples examined, 16.4% (95% CI: 13.5 – 19.2) contained Listeria species. When specific allocated sample size for each variable was considered, Listeria species were present in 42.5% (95% CI: 33.6 – 51.4), 14.5% (95% CI: 9.6 – 19.4), 23.1% (95% CI: 11.5 – 34.7), 13.5% (95% CI: 4.1 – 22.8) and 10.0% (95% CI: 3.4 – 16.6) of poultry samples, beef samples, RTE deli meats, lettuce, and environmental samples respectively. The proportions of Listeria species were L. innocua 67.2%, L. monocytogenes 21.5%, L. ivanovii 5.6%, L. seeligeri 3.7%, and L.
v
marthii 1.9%. Considering surface samples, those from poultry had a 60% contamination rate compared to cloacal samples, which was at 25.0%. Among samples from beef, interior samples were more contaminated at 17.0% than exterior surfaces at 12.0%. Isolation of Listeria species was not recorded from tilapia fish and environmental swabs from beef abattoirs. Furthermore, L. seeligeri was only recorded in lettuce vegetables. At WGS, all 42 (100%) isolates expressed intrinsic resistant genes fosX (resistance to fosfomycin) and lmo0919 (resistance to lincosamides) with only 17.5% expressing the Tet(M) (resistance to tetracycline) resistant genes. While only one isolate, 42 (2%) recorded dfrE (resistance to trimethoprim), erm(B) (macrolide), lsa(A) (resistance to Lincosamide, streptogramin), Tet (L) (resistance to tetracycline).
Within its limits, this study has elucidated the occurrence of L. monocytogenes and other Listeria species across different food sources at different processing and value points in Zambia. The isolation of closely related genetic species clustering within and between food sources strongly intimates the potential occurrence of cross-contamination. To a greater extent, these findings strongly suggest the need for policy shift regarding pathogen tracking and monitoring in relation to food safety, food outbreak investigations, and applying transformative food systems.