Abstract
Listeria monocytogenes is a ubiquitous bacteria and causative agent of zoonotic listeriosis with high mortality. The consumption of contaminated animal-derived foods has been linked with both epidemic and sporadic listeriosis. In this work, a total of 64 L. monocytogenes isolates from 259 pork samples sold in 11 supermarket chains were identified and characterized by comparative whole-genome analysis. All isolates were delineated into eight clonal complexes (CCs), namely CC2, CC8, CC9, CC11, CC155, CC121, CC204, and CC619, spanning two lineages (I and II) and carrying 3–5 antibiotic-resistant genes (fosX, lnu, mprF, tetM, and dhfR). It is noted that Listeria pathogenicity island (LIPI)-1, LIPI-3, and LIPI-4 were distributed in all ST619 isolates from two supermarket chains that were closely related with clinical isolates (<40 SNP). Some of the isolates from different supermarket chains with 0 SNP difference indicated a common pork supply source. Notably, 57.81% of the strains carried types IB, IIA, or IIIB CRISPR-Cas system, CC121 isolates carried both types IB and IIA CRISPR-Cas systems, Cas proteins of CC155 isolates located between two CRISPR loci, each CC has unique organization of Cas proteins as well as CRISPR loci. CRISPR-Cas system-based subtyping improved discrimination of pork-derived L. monocytogenes isolates. Comparisons at the genome level contributed to understand the genetic diversities and variations among the isolates and provided insights into the genetic makeup and relatedness of these pathogens.
Highlights
Listeria monocytogenes is a Gram-positive, facultative intracellular pathogen that is ubiquitously distributed in the environment (Smith et al, 2019)
The L. monocytogenes contamination status of pork meat in 53 supermarkets belonging to 11 supermarket chains was investigated
A total of 64 L. monocytogenes strains were isolated from 259 pork samples (24.71%) in 53 supermarkets belonging to 11 supermarket chains, which were supplied from 14 slaughterhouses (Table 1, Supplementary Figures 1A,B, and Supplementary Table 1)
Summary
Listeria monocytogenes is a Gram-positive, facultative intracellular pathogen that is ubiquitously distributed in the environment (Smith et al, 2019). A wide variety of animal species can be infected by L. monocytogenes, including mammals, birds, fish and crustaceans Pigs rarely develop listeriosis when exposed to L. monocytogenes contaminated feed Chapter 3.9.6 – L. monocytogenes), while they may become carriers of L. monocytogenes, and the pathogen is transmissible to humans through the pig and pork production chain to cause human listeriosis (Félix et al, 2018). In South Africa, an outbreak claimed the lives of 193 patients caused by Listeria contaminated pork sausage in 2017 (Thomas et al, 2020). In France, an outbreak (32 cases, 10 deaths) occurred because of L. monocytogenes contamination in pork product in Diversity of Lm in Pork
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