Transmission of trained immunity and heterologous resistance to infections across generations.

Intergenerational inheritance of immune traits linked to epigenetic modifications has been demonstrated in plants and invertebrates. Here we provide evidence for transmission of trained immunity across generations to murine progeny that survived a sublethal systemic infection with Candida albicans or a zymosan challenge. The progeny of trained mice exhibited cellular, developmental, transcriptional and epigenetic changes associated with the bone marrow-resident myeloid effector and progenitor cell compartment. Moreover, the progeny of trained mice showed enhanced responsiveness to endotoxin challenge, alongside improved protection against systemic heterologous Escherichia coli and Listeria monocytogenes infections. Sperm DNA of parental male mice intravenously infected with the fungus C. albicans showed DNA methylation differences linked to immune gene loci. These results provide evidence for inheritance of trained immunity in mammals, enhancing protection against infections.

The NLRP6 Inflammasome Recognizes Lipoteichoic Acid and Regulates Gram-Positive Pathogen Infection.

The activator and composition of the NLRP6 inflammasome remain poorly understood. We find that lipoteichoic acid (LTA), a molecule produced by Gram-positive bacteria, binds and activates NLRP6. In response to cytosolic LTA or infection with Listeria monocytogenes, NLRP6 recruited caspase-11 and caspase-1 via the adaptor ASC. NLRP6 activation by LTA induced processing of caspase-11, which promoted caspase-1 activation and interleukin-1ß (IL-1ß)/IL-18 maturation in macrophages. Nlrp6-/- and Casp11-/- mice were less susceptible to L. monocytogenes infection, which was associated with reduced pathogen loads and impaired IL-18 production. Administration of IL-18 to Nlrp6-/- or Casp11-/- mice restored the susceptibility of mutant mice to L. monocytogenes infection. These results reveal a previously unrecognized innate immunity pathway triggered by cytosolic LTA that is sensed by NLRP6 and exacerbates systemic Gram-positive pathogen infection via the production of IL-18.

Citrulline depletion by ASS1 is required for proinflammatory macrophage activation and immune responses.

Citrulline can be converted into argininosuccinate by argininosuccinate synthetase (ASS1) in the urea cycle and the citrulline-nitric oxide cycle. However, the regulation and biological function of citrulline metabolism remain obscure in the immune system. Unexpectedly, we found that macrophage citrulline declines rapidly after interferon gamma (IFN-γ) and/or lipopolysaccharide (LPS) stimulation, which is required for efficient proinflammatory signaling activation. Mechanistically, IFN-γ and/or LPS stimulation promotes signal transducers and activators of transcription 1 (STAT1)-mediated ASS1 transcription and Janus kinase2 (JAK2)-mediated phosphorylation of ASS1 at tyrosine 87, thereby leading to citrulline depletion. Reciprocally, increased citrulline directly binds to JAK2 and inhibits JAK2-STAT1 signaling. Blockage of ASS1-mediated citrulline depletion suppresses the host defense against bacterial infection in vivo. We therefore define a central role for ASS1 in controlling inflammatory macrophage activation and antibacterial defense through depletion of cellular citrulline and, further, identify citrulline as an innate immune-signaling metabolite that engages a metabolic checkpoint for proinflammatory responses.

Commensal bacteria direct selective cargo sorting to promote symbiosis.

Mucosal immunity protects a host from intestinal inflammation and infection and is profoundly influenced by symbiotic bacteria. Here we report that in mice symbiotic bacteria directed selective cargo sorting in Paneth cells to promote symbiosis through Nod2, a cytosolic bacterial sensor, and the multifunctional protein kinase LRRK2, both encoded by inflammatory bowel disease (IBD)-associated genes. Commensals recruited Nod2 onto lysozyme-containing dense core vesicles (DCVs), which was required for DCV localization of LRRK2 and a small GTPase, Rab2a. Deficiency of Nod2, LRRK2 or Rab2a or depletion of commensals resulted in lysosomal degradation of lysozyme. Thus, commensal bacteria and host factors orchestrate the lysozyme-sorting process to protect the host from enteric infection, implicating Paneth cell dysfunction in IBD pathogenesis.

Sox2 functions as a sequence-specific DNA sensor in neutrophils to initiate innate immunity against microbial infection.

Neutrophils express Toll-like receptors (TLRs) for the recognition of conserved bacterial elements to initiate antimicrobial responses. However, whether other cytosolic DNA sensors are expressed by neutrophils remains elusive. Here we found constitutive expression of the transcription factor Sox2 in the cytoplasm of mouse and human neutrophils. Neutrophil-specific Sox2 deficiency exacerbated bacterial infection. Sox2 directly recognized microbial DNA through its high-mobility-group (HMG) domain. Upon challenge with bacterial DNA, Sox2 dimerization was needed to activate a complex of the kinase TAK1 and its binding partner TAB2, which led to activation of the transcription factors NF-κB and AP-1 in neutrophils. Deficiency in TAK1 or TAB2 impaired Sox2-mediated antibacterial immunity. Overall, we reveal a previously unrecognized role for Sox2 as a cytosolic sequence-specific DNA sensor in neutrophils, which might provide potential therapeutic strategies for the treatment of infectious diseases.

Alternative splicing induced by bacterial pore-forming toxins sharpens CIRBP-mediated cell response to Listeria infection.

Cell autonomous responses to intracellular bacteria largely depend on reorganization of gene expression. To gain isoform-level resolution of these modes of regulation, we combined long- and short-read transcriptomic analyses of the response of intestinal epithelial cells to infection by the foodborne pathogen Listeria monocytogenes. Among the most striking isoform-based types of regulation, expression of the cellular stress response regulator CIRBP (cold-inducible RNA-binding protein) and of several SRSFs (serine/arginine-rich splicing factors) switched from canonical transcripts to nonsense-mediated decay-sensitive isoforms by inclusion of 'poison exons'. We showed that damage to host cell membranes caused by bacterial pore-forming toxins (listeriolysin O, perfringolysin, streptolysin or aerolysin) led to the dephosphorylation of SRSFs via the inhibition of the kinase activity of CLK1, thereby driving CIRBP alternative splicing. CIRBP isoform usage was found to have consequences on infection, since selective repression of canonical CIRBP reduced intracellular bacterial load while that of the poison exon-containing isoform exacerbated it. Consistently, CIRBP-bound mRNAs were shifted towards stress-relevant transcripts in infected cells, with increased mRNA levels or reduced translation efficiency for some targets. Our results thus generalize the alternative splicing of CIRBP and SRSFs as a common response to biotic or abiotic stresses by extending its relevance to the context of bacterial infection.

Listeria monocytogenes exploits host exocytosis to promote cell-to-cell spread.

The facultative intracellular pathogen Listeria monocytogenes uses an actin-based motility process to spread within human tissues. Filamentous actin from the human cell forms a tail behind bacteria, propelling microbes through the cytoplasm. Motile bacteria remodel the host plasma membrane into protrusions that are internalized by neighboring cells. A critical unresolved question is whether generation of protrusions by Listeria involves stimulation of host processes apart from actin polymerization. Here we demonstrate that efficient protrusion formation in polarized epithelial cells involves bacterial subversion of host exocytosis. Confocal microscopy imaging indicated that exocytosis is up-regulated in protrusions of Listeria in a manner that depends on the host exocyst complex. Depletion of components of the exocyst complex by RNA interference inhibited the formation of Listeria protrusions and subsequent cell-to-cell spread of bacteria. Additional genetic studies indicated important roles for the exocyst regulators Rab8 and Rab11 in bacterial protrusion formation and spread. The secreted Listeria virulence factor InlC associated with the exocyst component Exo70 and mediated the recruitment of Exo70 to bacterial protrusions. Depletion of exocyst proteins reduced the length of Listeria protrusions, suggesting that the exocyst complex promotes protrusion elongation. Collectively, these results demonstrate that Listeria exploits host exocytosis to stimulate intercellular spread of bacteria.

A Comprehensive Virulence and Resistance Characteristics of Listeria monocytogenes Isolated from Fish and the Fish Industry Environment.

Listeria monocytogenes is an important pathogen, often associated with fish, that can adapt and survive in products and food processing plants, where it can persist for many years. It is a species characterized by diverse genotypic and phenotypic characteristics. Therefore, in this study, a total of 17 L. monocytogenes strains from fish and fish-processing environments in Poland were characterized for their relatedness, virulence profiles, and resistance genes. The Core Genome Multilocus Sequence Typing (cgMLST) analysis revealed that the most frequent serogroups were IIa and IIb; sequence types (ST) were ST6 and ST121; and clonal complexes (CC) were CC6 and CC121. Core genome multilocus sequence typing (cgMLST) analysis was applied to compare the present isolates with the publicly available genomes of L. monocytogenes strains recovered in Europe from humans with listeriosis. Despite differential genotypic subtypes, most strains had similar antimicrobial resistance profiles; however, some of genes were located on mobile genetic elements that could be transferred to commensal or pathogenic bacteria. The results of this study showed that molecular clones of tested strains were characteristic for L. monocytogenes isolated from similar sources. Nevertheless, it is worth emphasizing that they could present a major public health risk due to their close relation with strains isolated from human listeriosis.

Host syndecan-1 promotes listeriosis by inhibiting intravascular neutrophil extracellular traps.

Heparan sulfate proteoglycans (HSPGs) are at the forefront of host-microbe interactions. Molecular and cell-based studies suggest that HSPG-pathogen interactions promote pathogenesis by facilitating microbial attachment and invasion of host cells. However, the specific identity of HSPGs, precise mechanisms by which HSPGs promote pathogenesis, and the in vivo relevance of HSPG-pathogen interactions remain to be determined. HSPGs also modulate host responses to tissue injury and inflammation, but functions of HSPGs other than facilitating microbial attachment and internalization are understudied in infectious disease. Here we examined the role of syndecan-1 (Sdc1), a major cell surface HSPG of epithelial cells, in mouse models of Listeria monocytogenes (Lm) infection. We show that Sdc1-/- mice are significantly less susceptible to both intragastric and intravenous Lm infection compared to wild type (Wt) mice. This phenotype is not seen in Sdc3-/- or Sdc4-/- mice, indicating that ablation of Sdc1 causes a specific gain of function that enables mice to resist listeriosis. However, Sdc1 does not support Lm attachment or invasion of host cells, indicating that Sdc1 does not promote pathogenesis as a cell surface Lm receptor. Instead, Sdc1 inhibits the clearance of Lm before the bacterium gains access to its intracellular niche. Large intravascular aggregates of neutrophils and neutrophil extracellular traps (NETs) embedded with antimicrobial compounds are formed in Sdc1-/- livers, which trap and kill Lm. Lm infection induces Sdc1 shedding from the surface of hepatocytes in Wt livers, which is directly associated with the decrease in size of intravascular aggregated NETs. Furthermore, administration of purified Sdc1 ectodomains or DNase inhibits the formation of intravascular aggregated neutrophils and NETs and significantly increases the liver bacterial burden in Sdc1-/- mice. These data indicate that Lm induces Sdc1 shedding to subvert the activity of Sdc1 ectodomains to inhibit its clearance by intravascular aggregated NETs.

The AIM2 inflammasome is essential for host defense against cytosolic bacteria and DNA viruses.

Inflammasomes regulate the activity of caspase-1 and the maturation of interleukin 1beta (IL-1beta) and IL-18. AIM2 has been shown to bind DNA and engage the caspase-1-activating adaptor protein ASC to form a caspase-1-activating inflammasome. Using Aim2-deficient mice, we identify a central role for AIM2 in regulating caspase-1-dependent maturation of IL-1beta and IL-18, as well as pyroptosis, in response to synthetic double-stranded DNA. AIM2 was essential for inflammasome activation in response to Francisella tularensis, vaccinia virus and mouse cytomegalovirus and had a partial role in the sensing of Listeria monocytogenes. Moreover, production of IL-18 and natural killer cell-dependent production of interferon-gamma, events critical in the early control of virus replication, were dependent on AIM2 during mouse cytomegalovirus infection in vivo. Collectively, our observations demonstrate the importance of AIM2 in the sensing of both bacterial and viral pathogens and in triggering innate immunity.

Type 3 Innate Lymphoid Cells Direct Goblet Cell Differentiation via the LT-LTßR Pathway during Listeria Infection.

As a specialized subset of intestinal epithelial cells (IECs), goblet cells (GCs) play an important role during the antibacterial response via mucin production. However, the regulatory mechanisms involved in GC differentiation and function during infection, particularly the role of immune cell-IEC cross-talk, remain largely unknown. In this study, using Villin∆Ltbr conditional knockout mice, we demonstrate that LTßR, expressed on IECs, is required for GC hyperplasia and mucin 2 (MUC2) expression during Listeria infection for host defense but not homeostatic maintenance in the naive state. Analysis of single gene-deficient mice revealed that the ligand lymphotoxin (LT), but not LIGHT, and type 3 innate lymphoid cells (ILC3s), but not conventional T cells, are required for MUC2-dependent Listeria control. Conditional deficiency of LT in ILC3s further confirmed the importance of LT signals derived from ILC3s. Lack of ILC3-derived LT or IEC-derived LTßR resulted in the defective expression of genes related to GC differentiation but was not correlated with IEC proliferation and cell death, which were found to be normal by Ki-67 and Annexin V staining. In addition, the alternative NF-κB signaling pathway (involving RelB) in IECs was found to be required for the expression of GC differentiation-related genes and Muc2 and required for the anti-Listeria response. Therefore, our data together suggest a previously unrecognized ILC3-IEC interaction and LT-LTßR-RelB signaling axis governing GC differentiation and function during Listeria infection for host defense.

Mice Lacking the Purinergic Receptor P2X5 Exhibit Defective Inflammasome Activation and Early Susceptibility to Listeria monocytogenes.

P2X5 is a member of the P2X purinergic receptor family of ligand-gated cation channels and has recently been shown to regulate inflammatory bone loss. In this study, we report that P2X5 is a protective immune regulator during Listeria monocytogenes infection, as P2X5-deficient mice exhibit increased bacterial loads in the spleen and liver, increased tissue damage, and early (within 3-6 d) susceptibility to systemic L. monocytogenes infection. Whereas P2X5-deficient mice experience normal monocyte recruitment in response to L. monocytogenes, P2X5-deficient bone marrow-derived macrophages (BMMs) exhibit defective cytosolic killing of L. monocytogenes We further showed that P2X5 is required for L. monocytogenes-induced inflammasome activation and IL-1ß production and that defective L. monocytogenes killing in P2X5-deficient BMMs is substantially rescued by exogenous IL-1ß or IL-18. Finally, in vitro BMM killing and in vivo L. monocytogenes infection experiments employing either P2X7 deficiency or extracellular ATP depletion suggest that P2X5-dependent anti-L. monocytogenes immunity is independent of the ATP-P2X7 inflammasome activation pathway. Together, our findings elucidate a novel and specific role for P2X5 as a critical mediator of protective immunity.

Increased Listeria monocytogenes Dissemination and Altered Population Dynamics in Muc2-Deficient Mice.

The mucin Muc2 is a major constituent of the mucus layer that covers the intestinal epithelium and creates a barrier between epithelial cells and luminal commensal or pathogenic microorganisms. The Gram-positive foodborne pathogen Listeria monocytogenes can cause enteritis and also disseminate from the intestine to give rise to systemic disease. L. monocytogenes can bind to intestinal Muc2, but the influence of the Muc2 mucin barrier on L. monocytogenes intestinal colonization and systemic dissemination has not been explored. Here, we used an orogastric L. monocytogenes infection model to investigate the role of Muc2 in host defense against L. monocytogenes Compared to wild-type mice, we found that Muc2-/- mice exhibited heightened susceptibility to orogastric challenge with L. monocytogenes, with higher mortality, elevated colonic pathology, and increased pathogen burdens in both the intestinal tract and distal organs. In contrast, L. monocytogenes burdens were equivalent in wild-type and Muc2-/- animals when the pathogen was administered intraperitoneally, suggesting that systemic immune defects related to Muc2 deficiency do not explain the heightened pathogen dissemination observed in oral infections. Using a barcoded L. monocytogenes library to measure intrahost pathogen population dynamics, we found that Muc2-/- animals had larger pathogen founding population sizes in the intestine and distal sites than observed in wild-type animals. Comparisons of barcode frequencies suggested that the colon becomes the major source for seeding the internal organs in Muc2-/- animals. Together, our findings reveal that Muc2 mucin plays a key role in controlling L. monocytogenes colonization, dissemination, and population dynamics.

IFN-ß, but not IFN-α, is Responsible for the Pro-Bacterial Effect of Type I Interferon.

BACKGROUND/AIMS: During an immune response, type I interferon (IFN-I) signaling induces a wide range of changes, including those which are required to overcome viral infection and those which suppress cytotoxic T cells to avoid immunopathology. During certain bacterial infections, IFN-I signaling exerts largely detrimental effects. Although the IFN-I family of proteins all share one common receptor, biologic responses to signaling vary depending on IFN-I subtype. Here, we asked if one IFN-I subtype dominates the pro-bacterial effect of IFN-I signaling and found that control of Listeria monocytogenes (L.m.) infection is more strongly suppressed by IFN-ß than IFN-α. METHODS: To study this, we measured bacterial titers in IFNAR-/-, IFN-ß­/­, Stat2-/-, Usp18fl/fl and Usp18fl/fl x CD11c-Cre mice models in addition to IFN-I blocking antibodies. Moreover, we measured interferon stimulated genes in bone marrow derived dendritic cells after treatment with IFN-α4 and IFN-ß. RESULTS: Specifically, we show that genetic deletion of IFN-ß or antibody-mediated IFN-ß neutralization was sufficient to reduce bacterial titers to levels similar to those observed in mice that completely lack IFN-I signaling (IFNAR-/- mice). However, IFN-α blockade failed to significantly reduce L.m. titers, suggesting that IFN-ß is the dominant IFN-I subtype responsible for the pro-bacterial effect of IFN-I. Mechanistically, when focusing on IFN-I signals to dendritic cells, we found that IFN-ß induces ISGs more robustly than IFN-α, including USP18, the protein we previously identified as driving the pro-bacterial effects of IFN-I. Further, we found that this induction was STAT1/STAT2 heterodimer- or STAT2/STAT2 homodimer-dependent, as STAT2-deficient mice were more resistant to L.m. infection. CONCLUSION: In conclusion, IFN-Β is the principal member of the IFN-I family responsible for driving the pro-bacterial effect of IFN-I.

Coordination of transcriptional and translational regulations in human epithelial cells infected by Listeria monocytogenes.

The invasion of mammalian cells by intracellular bacterial pathogens reshuffles their gene expression and functions; however, we lack dynamic insight into the distinct control levels that shape the host response. Here, we have addressed the respective contribution of transcriptional and translational regulations during a time-course of infection of human intestinal epithelial cells by an epidemic strain of Listeria monocytogenes, using transcriptome analysis paralleled with ribosome profiling. Upregulations were dominated by early transcriptional activation of pro-inflammatory genes, whereas translation inhibition appeared as the major driver of downregulations. Instead of a widespread but transient shutoff, translation inhibition affected specifically and durably transcripts encoding components of the translation machinery harbouring a 5'-terminal oligopyrimidine motif. Pre-silencing the most repressed target gene (PABPC1) slowed down the intracellular multiplication of Listeria monocytogenes, suggesting that the infected host cell can benefit from the repression of genes involved in protein synthesis and thereby better control infection.

Nuclear carbonic anhydrase 6B associates with PRMT5 to epigenetically promote IL-12 expression in innate response.

Interleukin-12 (IL-12) is critical for induction of protective immunity against intracellular bacterial infection. However, the mechanisms for efficient induction of IL-12 in innate response remain poorly understood. Here we report that the B type of carbonic anhydrase 6 (Car6-b, which encoded CA-VI B) is essential for host defense against Listeria monocytogenes (LM) infection by epigenetically promoting IL-12 expression independent of its carbonic anhydrase activity. Deficiency of Car6-b attenuated IL-12 production upon LM infection both in vitro and in vivo. Car6-/- mice were more susceptible to LM infection with less production of IL-12. Mechanistically, the nuclear localized CA-VI B selectively promotes IL-12 expression by interaction with protein arginine N-methyltransferase 5 (PRMT5), which reduces symmetric dimethylation of histone H3 arginine 8 modification (H3R8me2s) at Il12 promoters to facilitate chromatin accessibility, selectively enhancing c-Rel binding to the Il12b promoter. Our findings add insights to the epigenetic regulation of IL-12 induction in innate immunity.

SNX8 mediates IFNγ-triggered noncanonical signaling pathway and host defense against Listeria monocytogenes.

IFNγ is a cytokine that plays a key role in host defense against intracellular pathogens. In addition to the canonical JAK-STAT1 pathway, IFNγ also activates an IKKß-mediated noncanonical signaling pathway that is essential for induction of a subset of downstream effector genes. The molecular mechanisms and functional significance of this IFNγ-triggered noncanonical pathway remains enigmatic. Here, we identified sorting nexin 8 (SNX8) as an important component of the IFNγ-triggered noncanonical signaling pathway. SNX8-deficiency impaired IFNγ-triggered induction of a subset of downstream genes. Snx8-/- mice infected with Listeria monocytogenes exhibited lower serum cytokine levels and higher bacterial loads in the livers and spleens, resulting in higher lethality. Mechanistically, SNX8 interacted with JAK1 and IKKß and promoted their association. IFNγ induced JAK1-mediated phosphorylation of SNX8 at Tyr95 and Tyr126, which promoted the recruitment of IKKß to the JAK1 complex. SNX8-deficiency impaired IFNγ-induced oligomerization and autophosphorylation of IKKß at Ser177, which is critical for selective induction of downstream genes. Our findings suggest that SNX8 acts as a link for IFNγ-triggered noncanonical signaling pathway, which induces a subset of downstream genes important for host defense against L. monocytogenes infection.

Down regulation of macrophage IFNGR1 exacerbates systemic L. monocytogenes infection.

Interferons (IFNs) target macrophages to regulate inflammation and resistance to microbial infections. The type II IFN (IFNγ) acts on a cell surface receptor (IFNGR) to promote gene expression that enhance macrophage inflammatory and anti-microbial activity. Type I IFNs can dampen macrophage responsiveness to IFNγ and are associated with increased susceptibility to numerous bacterial infections. The precise mechanisms responsible for these effects remain unclear. Type I IFNs silence macrophage ifngr1 transcription and thus reduce cell surface expression of IFNGR1. To test how these events might impact macrophage activation and host resistance during bacterial infection, we developed transgenic mice that express a functional FLAG-tagged IFNGR1 (fGR1) driven by a macrophage-specific promoter. Macrophages from fGR1 mice expressed physiologic levels of cell surface IFNGR1 at steady state and responded equivalently to WT C57Bl/6 macrophages when treated with IFNγ alone. However, fGR1 macrophages retained cell surface IFNGR1 and showed enhanced responsiveness to IFNγ in the presence of type I IFNs. When fGR1 mice were infected with the bacterium Listeria monocytogenes their resistance was significantly increased, despite normal type I and II IFN production. Enhanced resistance was dependent on IFNγ and associated with increased macrophage activation and antimicrobial function. These results argue that down regulation of myeloid cell IFNGR1 is an important mechanism by which type I IFNs suppress inflammatory and anti-bacterial functions of macrophages.

Nonconventional initiation complex assembly by STAT and NF-kappaB transcription factors regulates nitric oxide synthase expression.

Transcriptional regulation of the Nos2 gene encoding inducible nitric oxide synthase (iNOS) requires type I interferon (IFN-I) signaling and additional signals emanating from pattern recognition receptors. Here we showed sequential and cooperative contributions of the transcription factors ISGF3 (a complex containing STAT1, STAT2, and IRF9 subunits) and NF-kappaB to the transcriptional induction of the Nos2 gene in macrophages infected with the intracellular bacterial pathogen Listeria monocytogenes. NF-kappaB preceded ISGF3 at the Nos2 promoter and generated a transcriptional memory effect by depositing basal transcription factor TFIIH with the associated CDK7 kinase for serine 5 phosphorylation of the RNA polymerase II (pol II) carboxyterminal domain (CTD). Subsequent to TFIIH deposition by NF-kappaB, ISGF3 attracted the pol II enzyme and phosphorylation at CTD S5 occurred. Thus, STATs and NF-kappaB cooperate through pol II promoter recruitment and the phosphorylation of its CTD, respectively, as a prerequisite for productive elongation of iNOS mRNA.

Case report: whole genome sequencing based investigation of maternal-neonatal listeriosis in Sichuan, China.

BACKGROUND: Neonatal listeriosis is a rare but severe disease manifesting as septicemia and central nervous system (CNS) infections with a high fatality rate of around 20 to 30%. Whole genome sequencing (WGS) is a promising technique for pathogen identification and infection source tracing with its high resolution. CASE PRESENTATION: A case of neonatal sepsis with listeriosis was reported with positive blood culture for Listeria monocytogenes. The case was investigated to confirm the vertical transmission of the infection and identify the potential food source of the maternal L. monocytogenes infection using WGS. L. monocytogenes was isolated from the neonate's blood sample the day after caesarean delivery and from the mother's genital and pudenda swab samples 5 days and 13 days after caesarean delivery. WGS showed that the isolate from the neonate was identical to the genome type of the isolates from the mother, with only one of the 4 isolates from the mother differing by one single nucleotide polymorphism (SNP). By WGS, one L. monocytogenes isolate from a ready-to-eat (RTE) meat sample in the patients' community market shared the same sequence type but was ruled out as the cause of infection, with 57 SNP differences to the strain causing the maternal-neonatal infection. The food isolate also carried a novel plasmid pLM1686 that harbored heavy metal resistance genes. After caesarean section, the mother was treated with a third generation cephalosporin which L. monocytogenes is naturally resistant to, which may explain why genital and pudenda swabs were still culture-positive for L. monocytogenes 13 days after delivery. CONCLUSIONS: Genital swab culture for L. monocytogenes had been informative in the diagnosis of maternal listeriosis in this case. The high resolution of WGS confirmed the maternal-neonatal transmission of L. monocytogenes infection and ruled out the L. monocytogenes contaminated RTE meat from the local market as the direct source of the mother's infection.