Listeria monocytogenes in ready to eat meat products from Zambia: phenotypical and genomic characterization of isolates

Abstract

The contamination of ready to eat foods (RTE) products due to <i>Listeria monocytogenes</i> could compromise the products safety becoming a great risk for the consumers. The high presence of <i>L. monocytogenes</i> in RTE products has been described worldwide, but few data are available about these products from African countries. The aims of this study were to report the presence of <i>L. monocytogenes</i> in Zambian RTE products, providing genomic characterization and data on similarity with African circulating strains using whole genome sequencing (WGS). A total of 304 RTE products, produced by different Zambian manufacturers, were purchased at retail, from major supermarkets located in Lusaka, Zambia, comprising 130 dairy and 174 meat products. <i>L. monocytogenes</i> was detected only in 18 (10.3%) RTE meat products of the 174 samples tested. The MLST analysis grouped the 18 <i>L. monocytogenes</i> isolates in 7 clonal complexes (CCs): CC1 (<i>n</i> = 5), CC2 (<i>n</i> = 4), CC9 (<i>n</i> = 4), CC5 (<i>n</i> = 2), CC121 (<i>n</i> = 1), CC155 (<i>n</i> = 1), and CC3 (<i>n</i> = 1). According to the cgMLST results, several clusters were detected, in particular belonging to hyper-virulent clones CC1 and CC2. Regarding the virulence factors, a complete <i>L. monocytogenes</i> Pathogenicity Island 3 (LIPI-3) was present both in the CC1 and CC3, in addition to LIPI-1. Several resistance genes and mobile genetic elements were detected, including Stress Islands, the <i>bcrABC</i> cassette and <i>Tn6188</i>_qac transposon, plasmids and intact prophages. Despite being a first preliminary work with a limited number of samples and isolates, this study helped to increase existing knowledge on contaminated RTE products in Zambia, confirming the presence of hyper-virulent <i>L. monocytogenes</i> CCs, which could play an important role in human diseases, posing a public health concern for consumers.