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

• Few data on Listeria monocytogenes are available from African countries. • Listeria monocytogenes CC9 was the main clone isolated from African meat products. • Hyper-virulent CC1 Listeria monocytogenes was detected in Sudan meat products. Although one of the biggest listeriosis outbreaks was reported in South Africa, due to 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 L. monocytogenes presence in African RTE meat products and food environments, posing a public health concern for consumers, mainly linked to CC1 strain presence, known to be a hyper-virulent clone. Moreover, the presence of L. monocytogenes strains harbouring several resistance factors, such as the CC9 clone, could help these strains to adapt, survive and persist.