Results on Listeria monocytogenes Strains From Ready-to-Eat Meat Products and Food Production Environments in Namibia, Sudan, and Zambia: A Focus on Genomic Characterization of Strains

Although one of the biggest listeriosis outbreaks was reported in South Africa, due to a ready-to-eat (RTE) meat product, to date, very few data on L. monocytogenes in foods and food environments are available from other African countries. The aims of this study were to document L. monocytogenes presence in RTE products and food environments from Namibia, Sudan, and Zambia, provide isolates' genomic characterization, and evaluate genomic similarity using data available at the Italian National Reference Laboratory for L. monocytogenes database. A total of 768 samples, including RTE meat products (n = 405), environmental swabs (n = 228), and frozen chicken (n = 135), were collected and tested for Listeria spp. and L. monocytogenes by African partners. Listeria spp. presence was observed mainly in Zambia (38.7%; n = 41/106), followed by Sudan (5.0%; n = 24/480) and Namibia (3.3%; n = 6/182), mostly related to RTE meat products (10.1%; n = 41/405). MALDI-TOF confirmed 14 of 71 strains as L. monocytogenes (n = 12 from meat RTE; n = 2 from environments) and MLST identified six CCs: CC9 (n = 7), CC1 (n = 3), CC3 (n = 1), CC37 (n = 1), CC121 (n = 1), and CC31 (n = 1). A complete L. monocytogenes Pathogenicity Island 3 (LIPI-3) was observed in CC1 and CC3 strains, in addition to LIPI-1, which was identified in all 14 strains. Several resistance factors were detected, including stress islands (SSI-1 and SSI-2), Tn6188_qac, cadA, and bcr genes. Furthermore, three cgMLST clusters were detected: two for CC9 from Zambia, one for CC1 from Sudan, all related to RTE foods. This study confirmed the presence of L. monocytogenes in African RTE meat products and food environments, posing a public health concern for consumers, mainly linked to the presence of CC1 strain, known to be a hyper-virulent clone. Moreover, the presence of L. monocytogenes strains harboring several resistance factors, such as the CC9 clone, could help these strains to adapt, survive, and persist.