Listeria monocytogenes Isolated from Illegally Imported Food Products into the European Union Harbor Different Virulence Factor Variants

Abstract

Unregulated international flow of foods poses a danger to human health, as it may be contaminated with pathogens. Recent studies have investigated neglected routes of pathogen transmission and reported the occurrence of Listeria monocytogenes in food illegally imported into the European Union (EU), either confiscated at four international airports or sold illegally on the Romanian black market. In this study we investigated the genotype diversity and the amino acid sequence variability of three main virulence factors of 57 L. monocytogenes isolates. These isolates were derived from 1474 food samples illegally imported into the EU and originated from 17 different countries. Multilocus sequence typing revealed 16 different sequence types (STs) indicating moderate genotype diversity. The most prevalent STs were ST2, ST9, and ST121. The pulsed-field gel electrophoresis (PFGE) analysis resulted in 34 unique pulsotypes. PFGE types assigned to the most prevalent STs (ST2, ST9, and ST121) were highly related in their genetic fingerprint. Internalin A (InlA) was present in 20 variants, including six truncated InlA variants, all harbored by isolates of ST9 and ST121. We detected eight ST-specific listeriolysin O (LLO) variants, and among them, one truncated form. The actin-assembly-inducing protein ActA was present in 15 different ST-specific variants, including four ActA variants with an internal truncation. In conclusion, this study shows that L. monocytogenes, isolated from illegally imported food, have moderate genotype diversity, but diverse virulence factors variants, mainly of InlA.

Isolation, Potential Virulence, and Population Diversity of Listeria monocytogenes From Meat and Meat Products in China

“…Our MLST analysis results showed that five CCs were the most prevalent: CC9 ( n = 123 isolates; 26.9%) and CC8 ( n = 82; 17.9%), followed by CC87 ( n = 70; 15.3%), CC155 ( n = 43, 9.4%), and CC121 ( n = 35; 7.6%). These results were consistent with those of previous studies in China (Wang et al, 2012; Li et al, 2018a), France (Felix et al, 2018), the European Union (Rychli et al, 2018), and Spain (Martin et al, 2014). The most prevalent ST was ST9 (26.9%), followed by ST8 (17.9%), ST87 (15.3%), ST155 (9.4%), and ST121 (7.6%) in this study.…”

Heterogeneity, Characteristics, and Public Health Implications of Listeria monocytogenes in Ready-to-Eat Foods and Pasteurized Milk in China

“…Interestingly, six (100%) ST9/CC9 and one (25%) ST5/CC5 isolates harbored PMSCs in the inlA gene, concurrent with previous studies reported in China (Chen et al, 2018a(Chen et al, , 2019a. Similarly, the PMSCs in the inlA gene were frequent in ST121/CC121 strains, which were predominant in foods and associated environments (Ciolacu et al, 2015;Palma et al, 2017;Rychli et al, 2017Rychli et al, , 2018. These data indicate that the ST9 and ST121 strains predominant in foods may acquire PMSCs in the inlA gene.…”

Virulence characterization and comparative genomics of Listeria monocytogenes sequence type 155 strains

“…Twenty ST155 L. monocytogenes strains, including eleven food isolates and nine human clinical isolates, were used for in vitro virulence assays ( Table 1). The strains from the Unit of Food Microbiology, University of Veterinary Medicine Vienna were isolated in frame of two previous projects [21,47]. Additionally, we screened 477 strains of the internal strain collection by PCR targeting the CC155-specific gene LMLG_RS02400 according to Chenal-Francisque et al [48] and subsequently determined the MLST.…”