Susceptibility (re)-testing of a large collection of Listeria monocytogenes from foods in China from 2012 to 2015 and WGS characterization of resistant isolates

Clinical, molecular, and resistance features of Listeria monocytogenes in non-perinatal patients with listeriosis: 8-year retrospective data from four tertiary hospitals in Shandong, China

Background

Listeriosis, caused by Listeria monocytogenes (L. monocytogenes), is a severe infectious disease with high hospitalization and fatality rates. Urgent epidemiological studies on this disease with geographic variability are needed, particularly in developing countries.

Methods

This study included non-perinatal patients with listeriosis from four tertiary centers in Shandong, China. Data on demographics, clinical characteristics, and outcomes were collected retrospectively over 8 years (2015-2022).

Results

Among 292,254 non-perinatal patients, 27 listeriosis cases were identified, resulting in an incidence of nine cases per 100,000 admissions. Patients had a median age of 56 years, with 66.7% having comorbidities. Fever was the most common symptom (88.9%), and 44.4% had central nervous system involvement. Most patients (26/24; 96.3%) received antibiotics, 37.0% received monotherapy and 59.3% combination therapy. The mortality rate was 22.2%. The antimicrobial susceptibility test showed that 25 strains were sensitive to most antibiotics. Multilocus sequence typing revealed nine sequence types (ST), predominantly ST8 (44.4%), and serogroup 1/2a is the most common serogroup (66.7%).

Conclusions

This study provides valuable insights into the clinical and molecular features of L. monocytogenes in non-perinatal patients with listeriosis. The findings demonstrated the predominance of serogroup 1/2a and ST8. Despite low resistance and appropriate treatment, listeriosis remains associated with a significant mortality rate, emphasizing the need for timely diagnosis and effective management strategies.

Sporadic Listeriosis Cases, Genotypic Characteristics, and Antibiotic Resistance of Associated Listeria monocytogenes Isolates in Zhejiang Province, China (2016 - 2022)

Listeria monocytogenes (L. monocytogenes) is an important foodborne pathogen. In this study, 41 sporadic listeriosis cases were collected during 2016-2022, including 92.7% of invasive cases and 56.1% of pregnancy-associated cases. The age of cases ranged from 0 days to 88 years, with the majority occurring in individuals aged 20 to <30 years. Serotype 1/2 b was most prevalent among 43 L. monocytogenes isolates, followed by 1/2 a, 4 b, and 3a. Sixteen clonal complexes (CCs) were determined. CC87 occupied the top slot. Genome sequencing-based phylogeny results indicated that Chinese CC1, CC8, and CC87 isolates mostly clustered in clades separating from isolates from other countries. Meanwhile, a few Chinese isolates participated in cocirculating CC1, CC8, and CC87 in Asia, Europe, Africa, South America, North America, and Oceania. All isolates harbored LIPI-1 while LIPI-2 was absent. LIPI-3 and LIPI-4 exhibited an apparent relationship with lineage and CCs. It was notably that CC4, CC224, and CC619 carried both LIPI-3 and LIPI-4. inlB, inlC, inlH, inlK, ipeA, srtA, dltA, lap, ami, fbpA, stp, oatA, intA, prsA2, lgt, hpt, iplA1, bsh, mdrT, mdrM, and brtA existed in all isolates. The percentages of inlA, inlF, inlJ, aut, vip were 97.7%, 97.7%, 97.7%, 83.7%, and 83.7%. A premature stop codon mutation of position 1474(C→T) was detected, resulting in a truncated InlA with 491 aa. High susceptibility to penicillin (100%), ampicillin (100%), gentamicin (100%), erythromycin (100%), daptomycin (100%), meropenem (100%), trimethoprim-sulfamethoxazole (100%), vancomycin (97.7%), tetacycline (97.7%), chloramphenicol (97.7%), and ciprofloxacin (90.7%) was demonstrated. lin and fosX were present in 93.0% of the isolates, respectively. tetM and ermB were also detected. This comprehensive study enriched the understanding of listeriosis cases and diversity of clinical isolates, meanwhile, indicated the spread characteristics of CC1, CC8, and CC87 in China based on phylogeny analysis, providing fundamental data for developing targeting food safety interventions to prevent listeriosis.

Genetic diversity of Listeria monocytogenes from seafood products, its processing environment, and clinical origin in the Western Cape, South Africa using whole genome sequencing

Listeria monocytogenes is a concern in seafood and its food processing environment (FPE). Several outbreaks globally have been linked to various types of seafood. Genetic profiling of L. monocytogenes is valuable to track bacterial contamination throughout the FPE and in understanding persistence mechanisms, with limited studies from South Africa. Forty-six L. monocytogenes isolates from origins: Fish/seafood products (n = 32) (salmon, smoked trout, fresh hake, oysters), the FPE (n = 6), and clinical (n = 8) were included in this study. Lineage typing, antibiotic susceptibility testing, and screening for two genes (bcrABC and emrC) conferring sanitizer tolerance was conducted. The seafood and FPE isolates originated from seven different factories processing various seafood products with undetermined origin. All clinical isolates were categorized as lineage I, and seafood and FPE isolates were mostly categorized into lineage II (p < 0.01). Seafood and FPE isolates (53%) carried the bcrABC gene cassette and one fish isolate, the emrC gene. A subset, n = 24, was grouped into serotypes, sequence types (STs), and clonal complexes (CCs) with whole genome sequencing (WGS). Eight CCs and ten STs were identified. All clinical isolates belonged to serogroup 4b, hypervirulent CC1. CC121 was the most prevalent in isolates from food and the FPE. All isolates carried Listeria pathogenicity islands (LIPI) 1 and 2. LIPI-3 and LIPI-4 were found in certain isolates. We identified genetic determinants linked to enhanced survival in the FPE, including stress survival islets (SSI) and genes conferring tolerance to sanitizers. SSI-1 was found in 44% isolates from seafood and the FPE. SSI-2 was found in all the ST121 seafood isolates. Isolates (42%) harbored transposon Tn1688_qac (ermC), conferring tolerance to quaternary ammonium compounds. Five plasmids were identified in 13 isolates from seafood and the FPE. This is the first One Health study reporting on L. monocytogenes genetic diversity, virulence and resistance profiles from various types of seafood and its FPE in South Africa.

Phenotypic and genotypic antimicrobial resistance of Listeria spp. in Spain

Listeriosis is a zoonotic disease caused by Listeria monocytogenes and Listeria ivanovii. The genus Listeria currently includes 27 recognized species and is found throughout the environment. The number of systematic studies on antimicrobial resistance in L. monocytogenes isolates from domestic farms using antimicrobial substances is limited. Importantly, dairy ruminant farms are reservoir of hypervirulent lineage I L. monocytogenes isolates, previously associated with human clinical cases. Considering that the classes of antibiotics used in food-producing domestic animals are frequently the same or closely related to those used in human medicine, studies about the impact of antibiotic use on the acquisition of antibiotic resistance in Listeria spp. in domestic animal farms are, therefore, of high importance. Here, susceptibility to 25 antibiotics was determined. Eighty-one animal-related, 35 food and 21 human pathogenic Listeria spp. isolates and 114 animal-related non-pathogenic Listeria spp. isolates were tested. Whole genome sequencing data was used for molecular characterization. Regarding L. monocytogenes, 2 strains from the clinical-associated linage I showed resistance to erythromycin, both related to dairy ruminants. Acquired resistance to one antibiotic was exhibited in 1.5% of L. monocytogenes isolates compared with 14% of non-pathogenic Listeria spp. isolates. Resistance to tetracycline (7.9%), doxycycline (7.9%), penicillin (4.4%), and ampicillin (4.4%) were the most frequently observed in non-pathogenic Listeria spp. While resistance to two or more antibiotics (5.6%) was most common in Listeria spp., isolates, resistance to one antibiotic was also observed (1.6%). The present results show that non-pathogenic Listeria spp. harbour antimicrobial resistance genes.

Phenotypic and genotypic antimicrobial resistance of Listeria monocytogenes: an observational study in France

Background

Large-scale studies are needed to clarify antimicrobial resistance in the foodborne pathogen Listeria monocytogenes (Lm) and the effectiveness of listeriosis treatment options. Here we examined the antimicrobial resistance patterns in Lm over time and assessed genotype-phenotype concordances.

Methods

We analyzed 5339 Lm isolates (2908 clinical and 2431 food isolates) collected in France and overseas territories, between 2012 and 2019. Whole genome sequencing was performed for all isolates and antimicrobial resistance profiles inferred from draft assemblies. Antimicrobial susceptibility towards 22 antimicrobials was determined for all clinical isolates, and in food isolates with acquired resistance genes.

Findings

All tested isolates were resistant to at least 3 different classes of antimicrobials, consistent with Lm intrinsic traits. Acquired antimicrobial resistance in Lm was rare (2.23% isolates) and more prevalent in food (mainly lineage II) compared to clinical isolates (mainly lineage I) (3.74% vs 0.98%, p < 0.0001), and in isolates with disinfectants or stress resistance traits (e.g. bcrABC, 20.20% vs 7.20%, p < 0.0001), suggesting co-selection of resistance in food-production environments. Acquired antimicrobial resistance could be predicted from genomes with high accuracy (>99%), except for ciprofloxacin. Acquired antimicrobial phenotypes were towards tetracyclines (mostly due to tetM), trimethoprim (dfrD), lincosamides (lnuG), macrolides (ermB, mphB) and phenicols (fexA).

Interpretation

The reference treatment for listeriosis (aminopenicillins/aminoglycosides) remains effective, with no acquired resistance observed. Continuous surveillance of antimicrobial resistance in clinical and food isolates is crucial to detect the emergence of novel resistance.

Funding

Institut Pasteur, INSERM, Santé Publique France, Investissement d'Avenir program Laboratoire d'Excellence 'Integrative Biology of Emerging Infectious Diseases' (ANR-10-LABX-62-IBEID).

Clinical and Genomic Characteristics of a Clinical Listeria Monocytogenes ST120 Isolate Recovered from a Pregnant Woman

Background

Maternal-fetal listeriosis, caused by Listeria monocytogenes, is a rare but serious infection. Herein, we report the clinical and genomic characteristics of a clinical L. monocytogenes ST120 isolate recovered from a pregnant woman.

Methods

The clinical symptoms and treatment in pregnant woman were described in detail. Whole genome sequencing (WGS) was performed on the L. monocytogenes isolate SJZ_LM001, and the genomic characterization of the isolate was deeply analyzed.

Results

The clinical symptoms in pregnant women were mainly fever, and the placenta experienced severe inflammation. The pregnant woman was treated with ampicillin for effective anti-infective therapy. Genomic analysis showed that isolate SJZ_LM001 is sequence type (ST) 120, belong to clonal complex (CC)8 and lineage II of L. monocytogenes. Additionally, the isolates SJZ_LM001 harbored a novel plasmid pSJZ_LM001, which carried arsenical resistance genes (arsACD and acr3), and cadmium resistance genes (cadAC). Drug susceptibility testing showed that the isolate SJZ-LM001 was susceptible to ampicillin, meropenem, penicillin, and cotrimoxazole.

Conclusion

This is the first to identify a clinical case of infection in a pregnant woman caused by ST120 L. monocytogenes in China. These findings could benefit our understanding of the genomic characteristics of L. monocytogenes, and the pregnancy-related listeriosis and providing early diagnosis and effective targeted treatment.

Genomic and pathogenicity islands of Listeria monocytogenes-overview of selected aspects

Listeria monocytogenes causes listeriosis, a disease characterized by a high mortality rate (up to 30%). Since the pathogen is highly tolerant to changing conditions (high and low temperature, wide pH range, low availability of nutrients), it is widespread in the environment, e.g., water, soil, or food. L. monocytogenes possess a number of genes that determine its high virulence potential, i.e., genes involved in the intracellular cycle (e.g., prfA, hly, plcA, plcB, inlA, inlB), response to stress conditions (e.g., sigB, gadA, caspD, clpB, lmo1138), biofilm formation (e.g., agr, luxS), or resistance to disinfectants (e.g., emrELm, bcrABC, mdrL). Some genes are organized into genomic and pathogenicity islands. The islands LIPI-1 and LIPI-3 contain genes related to the infectious life cycle and survival in the food processing environment, while LGI-1 and LGI-2 potentially ensure survival and durability in the production environment. Researchers constantly have been searching for new genes determining the virulence of L. monocytogenes. Understanding the virulence potential of L. monocytogenes is an important element of public health protection, as highly pathogenic strains may be associated with outbreaks and the severity of listeriosis. This review summarizes the selected aspects of L. monocytogenes genomic and pathogenicity islands, and the importance of whole genome sequencing for epidemiological purposes.

Human Listeriosis

Listeria monocytogenes is a Gram-positive facultative intracellular pathogen that can cause severe invasive infections upon ingestion with contaminated food. Clinically, listerial disease, or listeriosis, most often presents as bacteremia, meningitis or meningoencephalitis, and pregnancy-associated infections manifesting as miscarriage or neonatal sepsis. Invasive listeriosis is life-threatening and a main cause of foodborne illness leading to hospital admissions in Western countries. Sources of contamination can be identified through international surveillance systems for foodborne bacteria and strains' genetic data sharing. Large-scale whole genome studies have increased our knowledge on the diversity and evolution of L. monocytogenes, while recent pathophysiological investigations have improved our mechanistic understanding of listeriosis. In this article, we present an overview of human listeriosis with particular focus on relevant features of the causative bacterium, epidemiology, risk groups, pathogenesis, clinical manifestations, and treatment and prevention.

Food for Thought: Proteomics for Meat Safety

Foodborne bacteria interconnect food and human health. Despite significant progress in food safety regulation, bacterial contamination is still a serious public health concern and the reason for significant commercial losses. The screening of the microbiome in meals is one of the main aspects of food production safety influencing the health of the end-consumers. Our research provides an overview of proteomics findings in the field of food safety made over the last decade. It was believed that proteomics offered an accurate snapshot of the complex networks of the major biological machines called proteins. The proteomic methods for the detection of pathogens were armed with bioinformatics algorithms, allowing us to map the data onto the genome and transcriptome. The mechanisms of the interaction between bacteria and their environment were elucidated with unprecedented sensitivity, specificity, and depth. Using our web-based tool ScanBious for automated publication analysis, we analyzed over 48,000 scientific articles on antibiotic and disinfectant resistance and highlighted the benefits of proteomics for the food safety field. The most promising approach to studying safety in food production is the combination of classical genomic and metagenomic approaches and the advantages provided by proteomic methods with the use of panoramic and targeted mass spectrometry.

The population structure and genetic diversity of Listeria monocytogenes ST9 strains based on genomic analysis

Listeria monocytogenes is a ubiquitous foodborne pathogen causing both invasive and non-invasive listeriosis. Sequence type (ST) 9 strains is common in food and food processing environments. In this study, the whole-genome sequences (WGS) of 207 ST9 isolates from different sources, geographical locations (14 countries), and isolated years were analyzed. The ST9 isolates were divided into three clusters after phylogenetic analysis; 67.63% of ST9 isolates contained putative plasmids with different sizes and genomic structure, the putative prophages inserted in the chromosome at ten hotspots, and seven types of premature stop codon (PMSC) mutations in inlA were found in 81.86% of the ST9 isolates. In addition, 78.26% of ST9 isolates harbored Tn554-like elements carrying arsenic resistance genes. All the ST9 isolates conservatively contained environment-resistance genes on the chromosome. This analysis of population structures and features of ST9 isolates was aimed to help develop effective strategies to control this prevalent pathogen in the food chain.

Pervasive Listeria monocytogenes Is Common in the Norwegian Food System and Is Associated with Increased Prevalence of Stress Survival and Resistance Determinants

To investigate the diversity, distribution, persistence, and prevalence of stress survival and resistance genes of Listeria monocytogenes clones dominating in food processing environments in Norway, genome sequences from 769 L. monocytogenes isolates from food industry environments, foods, and raw materials (512 of which were sequenced in the present study) were subjected to whole-genome multilocus sequence typing (wgMLST), single-nucleotide polymorphism (SNP), and comparative genomic analyses. The data set comprised isolates from nine meat and six salmon processing facilities in Norway collected over a period of three decades. The most prevalent clonal complex (CC) was CC121, found in 10 factories, followed by CC7, CC8, and CC9, found in 7 factories each. Overall, 72% of the isolates were classified as persistent, showing 20 or fewer wgMLST allelic differences toward an isolate found in the same factory in a different calendar year. Moreover, over half of the isolates (56%) showed this level of genetic similarity toward an isolate collected from a different food processing facility. These were designated as pervasive strains, defined as clusters with the same level of genetic similarity as persistent strains but isolated from different factories. The prevalence of genetic determinants associated with increased survival in food processing environments, including heavy metal and biocide resistance determinants, stress response genes, and inlA truncation mutations, showed a highly significant increase among pervasive isolates but not among persistent isolates. Furthermore, these genes were significantly more prevalent among the isolates from food processing environments compared to in isolates from natural and rural environments (n = 218) and clinical isolates (n = 111) from Norway.

IMPORTANCEListeria monocytogenes can persist in food processing environments for months to decades and spread through the food system by, e.g., contaminated raw materials. Knowledge of the distribution and diversity of L. monocytogenes is important in outbreak investigations and is essential to effectively track and control this pathogen in the food system. The present study presents a comprehensive overview of the prevalence of persistent clones and of the diversity of L. monocytogenes in Norwegian food processing facilities. The results demonstrate extensive spread of highly similar strains throughout the Norwegian food system, in that 56% of the 769 collected isolates from food processing factories belonged to clusters of L. monocytogenes identified in more than one facility. These strains were associated with an overall increase in the prevalence of plasmids and determinants of heavy metal and biocide resistance, as well as other genetic elements associated with stress survival mechanisms and persistence.

Genomic Characterization of Clinical Listeria monocytogenes Isolates in Beijing, China

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.

Low-Level Tolerance to Antibiotic Trimethoprim in QAC-Adapted Subpopulations of Listeria monocytogenes

Between January and July 2021, there were as many as 30 recalls in the U.S. due to potential Listeria monocytogenes contamination from a variety of food products including muffins, kimchi, chicken salad, ready-to-eat chicken, smoked fish, mushrooms, queso fresco cheese, ice cream, turkey sandwiches, squash, and other foods. A contaminated food chain can serve as a potential vehicle for transmitting antibiotic resistant bacteria since there is a slow emergence of multi-drug antibiotic resistance in L. monocytogenes. Biocides are essential for safe food processing, but they may also induce unintended selective pressure at sublethal doses for the expression of antibiotic resistance in L. monocytogenes. To better understand the sources of such slow emergence of antibiotic resistance through biocide residues present in the food environments, we are working on the role of sublethal doses of commonly used biocides in defined broth and water models for understanding L. monocytogenes adaptation. We recently published the development of low-level tolerance to fluoroquinolone antibiotic ciprofloxacin in quaternary ammonium compound (QAC) adapted subpopulations of L. monocytogenes (Microorganisms 9, 1052). Of the six different antibiotics tested to determine heterologous stress adaptation in eight strains of L. monocytogenes, trimethoprim was the second one that exhibited low-level tolerance development after continuous exposure (by three approaches) to sublethal concentrations of QAC against actively growing planktonic cells of L. monocytogenes. When adapted to daily cycles of fixed or gradually increasing sublethal concentrations of QAC, we observed three main findings in eight L. monocytogenes strains against trimethoprim: (a) 3 of the 8 strains exhibited significant increase in short-range minimum inhibitory concentration (MIC) of trimethoprim by 1.7 to 2.5 fold in QAC-adapted subpopulations compared to non-adapted cells (p < 0.05); (b) 2 of the 8 strains exhibited significant increase in growth rate in trimethoprim (optical density (OD) by 600 nm at 12 h) by 1.4 to 4.8 fold in QAC-adapted subpopulations compared to non-adapted cells (p < 0.05); and (c) 5 of the 8 strains yielded significantly higher survival by 1.3-to-3.1 log CFU/mL in trimethoprim in QAC-adapted subpopulations compared to the non-adapted control (p < 0.05). However, for 3/8 strains of L. monocytogenes, there was no increase in the survival of QAC-adapted subpopulations compared to non-adapted control in trimethoprim. These findings suggest the potential formation of low-level trimethoprim tolerant subpopulations in some L. monocytogenes strains where QAC may be used widely. These experimental models are useful in developing early detection methods for tracking the slow emergence of antibiotic tolerant strains through food chain. Also, these findings are useful in understanding the predisposing conditions leading to slow emergence of antibiotic resistant strains of L. monocytogenes in various food production and food processing environments.

Whole Genome Analysis of Three Multi-Drug Resistant Listeria innocua and Genomic Insights Into Their Relatedness With Resistant Listeria monocytogenes

Listeria innocua are Gram-positive rod-shaped bacteria, which are not generally infectious as opposed to Listeria monocytogenes. However, the comparatively high genomic similarity between both along with on occasion, their coexistence in similar ecological niches may present the opportunity for resistance or virulence gene transfer. In this study, three multi-drug resistant L. innocua originally cultured from food were put forward for long-read genome sequencing. Chromosome and plasmid genomes were assembled and annotated. Analysis demonstrated that the resistant phenotypes correlated well with genotypes. Three plasmids pLI42, pLI203, and pLI47-1 were identified which harbor resistance islands. Sequence alignments suggested that plasmids pLI42 and pLI203 were highly similar to a previously sequenced L. monocytogenes plasmid pLR1. Similarly, another three types of resistance gene islands were observed on chromosome, including tet(M) gene islands (transposon Tn916 orthologs), dfrG gene islands and optrA-erm(A) gene islands. All three L. innocua isolates possessed listeria pathogenicity island-4 (LIPI-4) which is linked to cases of mengitis. Further genome environment and phylogenic analysis of regions flanking LIPI-4 of L. innocua and L. monocytogenes showed that these may have common origins and with the potential to transmit from the former. Our findings raise the possible need to include both L. monocytogenes and L. innocua in food surveillance programs so as to further understand of the origins of antimicrobial resistance and virulence markers of public health importance in L. monocytogenes.

Use of Bacteriophage Amended with CRISPR-Cas Systems to Combat Antimicrobial Resistance in the Bacterial Foodborne Pathogen Listeria monocytogenes

Listeria monocytogenes is a bacterial foodborne pathogen and the causative agent of the disease listeriosis, which though uncommon can result in severe symptoms such as meningitis, septicemia, stillbirths, and abortions and has a high case fatality rate. This pathogen can infect humans and other animals, resulting in massive health and economic impacts in the United States and globally. Listeriosis is treated with antimicrobials, typically a combination of a beta-lactam and an aminoglycoside, and L. monocytogenes has remained largely susceptible to the drugs of choice. However, there are several reports of antimicrobial resistance (AMR) in both L. monocytogenes and other Listeria species. Given the dire health outcomes associated with listeriosis, the prospect of antimicrobial-resistant L. monocytogenes is highly problematic for human and animal health. Developing effective tools for the control and elimination of L. monocytogenes, including strains with antimicrobial resistance, is of the utmost importance to prevent further dissemination of AMR in this pathogen. One tool that has shown great promise in combating antibiotic-resistant pathogens is the use of bacteriophages (phages), which are natural bacterial predators and horizontal gene transfer agents. Although native phages can be effective at killing antibiotic-resistant pathogens, limited host ranges and evolved resistance to phages can compromise their use in the efforts to mitigate the global AMR challenge. However, recent advances can allow the use of CRISPR-Cas (clustered regularly interspaced short palindromic repeats-CRISPR-associated proteins) to selectively target pathogens and their AMR determinants. Employment of CRISPR-Cas systems for phage amendment can overcome previous limitations in using phages as biocontrol and allow for the effective control of L. monocytogenes and its AMR determinants.

Listeriosis Cases and Genetic Diversity of Their L. monocytogenes Isolates in China, 2008-2019

Listeriosis, caused by Listeria monocytogenes, is a severe food-borne infection. The nationwide surveillance in China concerning listeriosis is urgently needed. In the present study, 144 L. monocytogenes isolates were collected from the samples of blood, cerebrospinal fluid (CSF), and fetal membrane/placenta in China for 12 years from 2008 to 2019. We summarized these listeriosis patients’ demographical and clinical features and outcomes. The susceptibility profile for 12 antibiotics was also determined by the broth microdilution method. Multilocus sequence typing (MLST) and serogroups of these listeria isolates were analyzed to designate epidemiological types. We enrolled 144 cases from 29 healthcare centers, including 96 maternal-neonatal infections, 33 cases of bacteremia, 13 cases of neurolisteriosis, and two cutaneous listeriosis. There were 31 (59.6%) fetal loss in 52 pregnant women and four (9.8%) neonatal death in 41 newborns. Among the 48 nonmaternal-neonatal cases, 12.5% (6/48) died, 41.7% (20/48) were female, and 64.6% (31/48) occurred in those with significant comorbidities. By MLST, the strains were distinguished into 23 individual sequence types (STs). The most prevalent ST was ST87 (49 isolates, 34.0%), followed by ST1 (18, 12.5%), ST8 (10, 6.9%), ST619 (9, 6.3%), ST7 (7, 4.9%) and ST3 (7, 4.9%). Furthermore, all L. monocytogenes isolates were uniformly susceptible to penicillin, ampicillin, and meropenem. In summary, our study highlights a high genotypic diversity of L. monocytogenes strains causing clinical listeriosis in China. Furthermore, a high prevalence of ST87 and ST1 in the listeriosis should be noted.

Ecogenetics of antibiotic resistance in Listeria monocytogenes

The acquisition process of antibiotic resistance in an otherwise susceptible organism is shaped by the ecology of the species. Unlike other relevant human pathogens, Listeria monocytogenes has maintained a high rate of susceptibility to the antibiotics used for decades to treat human and animal infections. However, L. monocytogenes can acquire antibiotic resistance genes from other organisms' plasmids and conjugative transposons. Ecological factors could account for its susceptibility. L. monocytogenes is ubiquitous in nature, most frequently including reservoirs unexposed to antibiotics, including intracellular sanctuaries. L. monocytogenes has a remarkably closed genome, reflecting limited community interactions, small population sizes and high niche specialization. The L. monocytogenes species is divided into variants that are specialized in small specific niches, which reduces the possibility of coexistence with potential donors of antibiotic resistance. Interactions with potential donors are also hampered by interspecies antagonism. However, occasional increases in population sizes (and thus the possibility of acquiring antibiotic resistance) can derive from selection of the species based on intrinsic or acquired resistance to antibiotics, biocides, heavy metals or by a natural tolerance to extreme conditions. High-quality surveillance of the emergence of resistance to the key drugs used in primary therapy is mandatory.

Genomic and Phenotypic Diversity of Listeria monocytogenes Causing Pregnancy-Associated Listeriosis from Zhejiang Province, China, 2016-2018

Introduction

There are few investigations describing the pregnancy-associated listeriosis in China, and the molecular characteristics of Listeria monocytogenes causing such infections remain largely unknown. We aim to investigate the phenotypic and genomic profiles of pregnancy-associated L. monocytogenes isolates and their association with isolates recovered from human and non-human in China.

Materials and Methods

In this study, we conducted a 3-year surveillance of listeriosis in a women's hospital in Zhejiang province, using whole genome sequencing and bioinformatics tools.

Results

From 2016 to 2018, we identified 13 clinical L. monocytogenes isolates. Among these pregnancy-associated isolates, we found seven sequence types (STs), with the prevalent STs of ST87 and ST7. Serotyping divided the strains into four serotypes, including serotype 1/2a, 1/2b, 3a, and 4b. Antimicrobial resistance testing showed that all the isolates were susceptible to 10 antibiotics. Comparative genomics analysis clearly classified our genome collection into four distinct evolutionary lineages with most isolates grouping into lineages I and II. Interestingly, we found three pairs of isolates with high identity, although no evident epidemiological association was observed.

Conclusion

This study reports for the first time the surveillance of pregnancy-associated listeriosis in Zhejiang province, China, which indicates that the infection rate is low in this region. Our findings provide insight into the evolution and genetic diversity of pregnancy-associated L. monocytogenes from Zhejiang province. Additional investigations involving more human and non-human isolates with a "one health" strategy are needed for prediction of the listeriosis risk associated with a typical prevalent clone in Zhejiang province, such as ST87.