Genomic Characterization of Clinical Listeria monocytogenes Isolates in Beijing, China

Abstract

Listeria monocytogenes is a foodborne human pathogen that affects public health worldwide. Whole-genome sequencing (WGS) can classify L. monocytogenes isolates and identify virulence islands and resistance genes potentially influencing infectivity. Herein, WGS was used to assess 151 L. monocytogenes isolates from 120 cases of clinical infection in Beijing, China, between 2014 and 2018. Most isolates were either serogroup 1/2a,3a or serogroup 1/2b,3b,7, with 25 multilocus sequence typing (MLST) types (STs) represented, of which ST8, ST87, and ST5 were the most common. Core-genome MLST (cgMLST) grouped the 151 isolates into 116 cgMLST types. The discriminatory power of cgMLST was greater than other subtypes, revealing that isolates from the same patient were highly related (only differing at one allele). Eighty-six isolates formed 30 complexes with ≤ 7 cgMLST alleles between neighboring isolates, suggesting possible outbreaks. Compared with isolates in the United States, ST8, ST121, ST619, ST87, and ST155 isolates were grouped into unified clades. All 151 isolates were positive for common virulence-associated loci, and 26 lineage I isolates harbored the pathogenicity island 3 (LIPI-3) locus, while 42 lineage I isolates harbored the complete LIPI-4 locus. Eleven ST619 isolates had both LIPI-3 and LIPI-4. Among the 151 isolates, 13 were resistant to at least one antibiotic, and no multidrug-resistant isolates were identified. Resistance phenotypes correlated with genotypes, apart from two meropenem resistance isolates. The findings provided insight into the nature of L. monocytogenes strains currently causing clinical disease in Beijing, and WGS analysis indicated possible outbreaks.

Genetic Diversity and Relationships of Listeria monocytogenes Serogroup IIa Isolated in Poland

“…The remaining seven strains, mainly recovered from RTE food, were grouped into three CCs, with single isolates in each ( Figure 1 ). L. monocytogenes of the CCs identified in the present study were also previously detected among 100 strains of IIa serogroup recovered from food but were also often isolated from humans with listeriosis [ 12 , 14 , 18 , 44 , 45 , 46 , 47 ].…”

“…The remaining seven strains, mainly recovered from RTE food, were grouped into three CCs, with single isolates in each (Figure 1). L. monocytogenes of the CCs identified in the present study were also previously detected among 100 strains of IIa serogroup recovered from food but were also often isolated from humans with listeriosis [12,14,18,[44][45][46][47]. Further analysis of WGS sequences revealed that all 100 current isolates were classified into eight sequence types, with the most prevalent ST155 (33; 33.0%), ST121 (30; 30.0%), and ST8 (28; 28.0%) (Figure 2).…”

“…L. monocytogenes of ST8, such as the characterized above ST121, was previously often isolated from food and food production areas, which suggests that strains of such sequence type can survive in adverse conditions present in such environments [ 13 , 74 , 77 , 79 , 80 ]. Furthermore, such isolates have probably increased virulence properties since they were also responsible for human listeriosis cases [ 47 , 59 , 81 , 82 ].…”

“…Only two CC8 isolates of cgMLST types CT750 and CT9837, both of food production environments origin, were positive for the Tn6188_qac ( ermC ) transposon involved in QAC and other various disinfectants resistance widely used in food production ( Table 2 ) [ 68 , 71 ]. Isolates belonging to CC8 were also previously identified in food and in humans suffering from listeriosis [ 18 , 26 , 45 , 46 , 47 , 83 ]. However, there are also studies in which none of the L. monocytogenes classified to CC8 was positive for the Tn6188_qac ( ermC ) marker [ 49 , 80 ].…”

PervasiveListeria monocytogenesare common in the Norwegian food system and associated with increased prevalence of stress survival and resistance determinants

“…Antibiotic resistance determinants present on mobile genetic elements appear to have low prevalence in L. monocytogenes isolated in Norway, as only one such antibiotic resistance gene was detected among the 1098 examined genomes (a tet(M) tetracycline resistance gene in a clinical isolate). This is lower than that recently reported among isolates from other countries (85)(86)(87)(88)(89)(90).…”