Neurotropic Lineage III Strains of Listeria monocytogenes Disseminate to the Brain without Reaching High Titer in the Blood

FengycinA-M3 Inhibits Listeria monocytogenes by Binding to Penicillin-Binding Protein 2B Targets to Disrupt Cell Structure

The contamination of food with Listeria monocytogenes threatens food safety and human health, and developing a novel, green, and safe antimicrobial substance will offer a new food preservation strategy. FengycinA-M3 is a novel lipid peptide with low cytotoxicity and resistance and has effective antibacterial activity against L. monocytogenes with a minimum inhibitory concentration (MIC) of 4 µg/mL. Further combined transcriptomics and proteomics analysis yielded 20 differentially expressed genes (DEGs). The MICs of the combined use of FengycinA-M3 and Cefalexin on L. monocytogenes were further determined as FengycinA-M3 (2 µg/mL) and Cefalexin (8 µg/mL) using the checkerboard method. In addition, FengycinA-M3 was found to play a role in delaying pork deterioration. This study explored the inhibitory effect of FengycinA-M3 on L. monocytogenes and its mechanism of action. FengycinA-M3 interacted with penicillin-binding protein 2B on the cell membrane of L. monocytogenes, destroying the permeability of the membrane, causing cell membrane rupture, thereby inhibiting the growth of L. monocytogenes. Overall, FengycinA-M3 is a promising candidate for preventing the emergence and spread of L. monocytogenes with potential applications in food processing.

From cytokines to chemokines: Understanding inflammatory signaling in bacterial meningitis

Bacterial meningitis is a serious central nervous system (CNS) infection, claiming millions of human lives annually around the globe. The deadly infection involves severe inflammation of the protective sheath of the brain, i.e., meninges, and sometimes also consists of the brain tissue, called meningoencephalitis. Several inflammatory pathways involved in the pathogenesis of meningitis caused by Streptococcus pneumoniae, Neisseria meningitidis, Escherichia coli, Haemophilus influenzae, Mycobacterium tuberculosis, Streptococcus suis, etc. are mentioned in the scientific literature. Many in-vitro and in-vivo analyses have shown that after the disruption of the blood-brain barrier (BBB), these pathogens trigger several inflammatory pathways including Toll-Like Receptor (TLR) signaling in response to Pathogen-Associated Molecular Patterns (PAMPs), Nucleotide oligomerization domain (NOD)-like receptor-mediated signaling, pneumolysin related signaling, NF-κB signaling and many other pathways that lead to pro-inflammatory cascade and subsequent cytokine release including interleukine (IL)-1β, tumor necrosis factor(TNF)-α, IL-6, IL-8, chemokine (C-X-C motif) ligand 1 (CXCL1) along with other mediators, leading to neuroinflammation. The activation of another protein complex, nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 (NLRP3) inflammasome, also takes place resulting in the maturation and release of IL-1β and IL-18, hence potentiating neuroinflammation. This review aims to outline the inflammatory signaling pathways associated with the pathogenesis of bacterial meningitis leading to extensive pathological changes in neurons, astrocytes, oligodendrocytes, and other central nervous system cells.

A 48-year-old man with fever, nauseous, vomiting, and dizzy: A CARE case report

RATIONALE

Listeria monocytogenes (LM) is an important foodborne bacterium, and LM meningoencephalitis is rare in clinical practice, with poor prognosis in severe patients. It is prone to misdiagnosis in clinical practice. We first reported a case of severe LM meningoencephalitis with muscle lesions and evaluated the comprehensive condition.

PATIENT CONCERNS

A 48-year-old man had a fever and was admitted to the neurology department due to dizziness, nausea, and vomiting for 20 days.

DIAGNOSES

LM meningoencephalitis complicated with muscle lesions.

INTERVENTIONS

We used moxifloxacin 0.4 g, qd, meropenem 2 g, q8h, and dexamethasone 10 mg, qd to reduce exudation and adhesion. Then due to consideration of side effects, we increased the dose of ampicillin by 2 g, q4h, stopped using meropenem and moxifloxacin, and turned to maintenance treatment with dexamethasone and ampicillin. We comprehensively managed his vital signs and physical organ functions, we also controlled some comorbidities. During the hospitalization period thereafter, we used intravenous anti-infection treatment with moxifloxacin 0.4 g, qd, ampicillin 0.5 g, q4h.

OUTCOMES

Half a year later, the reexamination showed only protein elevation in cerebrospinal fluid and hydrocephalus in MRI. Afterward, the symptoms did not recur again. The patient recovered well after discharge.

LESSONS

LM meningoencephalitis complicated with lower limb muscle lesions is clinically rare. This report focuses on relevant treatment plans, which provide value for the examination and comprehensive management of patients with LM infection in the future.

Complete genome of the Listeria monocytogenes strain AUF, used as a live listeriosis veterinary vaccine

Listeria monocytogenes (Lm) is a highly pathogenic bacterium that can cause listeriosis, a relatively rare food-borne infectious disease that affects farm, domestic, wild animals and humans as well. The infected livestock is the frequent sources of Lm. Vaccination is one of the methods of controlling listeriosis in target farm animals to prevent Lm-associated food contamination. Here we report the complete sequence of the Lm strain AUF attenuated from a fully-virulent Lm strain by ultraviolet irradiation, successfully used since the 1960s as a live whole-cell veterinary vaccine. The de novo assembled genome consists of a circular chromosome of 2,942,932 bp length, including more than 2,800 CDSs, 17 pseudogenes, 5 antibiotic resistance genes, and 56/92 virulence genes. Two wild Lm strains, the EGD and the 10403S that is also used in cancer Immunotherapy, were the closest homologs for the Lm strain AUF. Although all three strains belonged to different sequence types (ST), namely ST12, ST85, and ST1538, they were placed in the same genetic lineage II, CC7.

Temporal and spatial dynamics of Listeria monocytogenes central nervous system infection in mice

Listeria monocytogenes is a bacterial pathogen that can cause life-threatening central nervous system (CNS) infections. While mechanisms by which L. monocytogenes and other pathogens traffic to the brain have been studied, a quantitative understanding of the underlying dynamics of colonization and replication within the brain is still lacking. In this study, we used barcoded L. monocytogenes to quantify the bottlenecks and dissemination patterns that lead to cerebral infection. Following intravenous (IV) inoculation, multiple independent invasion events seeded all parts of the CNS from the blood, however, only one clone usually became dominant in the brain. Sequential IV inoculations and intracranial inoculations suggested that clones that had a temporal advantage (i.e., seeded the CNS first), rather than a spatial advantage (i.e., invaded a particular brain region), were the main drivers of clonal dominance. In a foodborne model of cerebral infection with immunocompromised mice, rare invasion events instead led to a highly infected yet monoclonal CNS. This restrictive bottleneck likely arose from pathogen transit into the blood, rather than directly from the blood to the brain. Collectively, our findings provide a detailed quantitative understanding of the L. monocytogenes population dynamics that lead to CNS infection and a framework for studying the dynamics of other cerebral infections.

Polarization- and Chaos-Game-Based Fingerprinting of Molecular Targets of Listeria Monocytogenes Vaccine and Fully Virulent Strains

Two approaches to the synthesis of 2D binary identifiers ("fingerprints") of DNA-associated symbol sequences are considered in this paper. One of these approaches is based on the simulation of polarization-dependent diffraction patterns formed by reading the modeled DNA-associated 2D phase-modulating structures with a coherent light beam. In this case, 2D binarized distributions of close-to-circular extreme polarization states are applied as fingerprints of analyzed nucleotide sequences. The second approach is based on the transformation of the DNA-associated chaos game representation (CGR) maps into finite-dimensional binary matrices. In both cases, the differences between the structures of the analyzed and reference symbol sequences are quantified by calculating the correlation coefficient of the synthesized binary matrices. A comparison of the approaches under consideration is carried out using symbol sequences corresponding to nucleotide sequences of the hly gene from the vaccine and wild-type strains of Listeria monocytogenes as the analyzed objects. These strains differ in terms of the number of substituted nucleotides in relation to the vaccine strain selected as a reference. The results of the performed analysis allow us to conclude that the identification of structural differences in the DNA-associated symbolic sequences is significantly more efficient when using the binary distributions of close-to-circular extreme polarization states. The approach given can be applicable for genetic differentiation immunized from vaccinated animals (DIVA).

Progressive cognitive impairment after recovery from neuroinvasive and non-neuroinvasive Listeria monocytogenes infection

Background

Neuro-cognitive impairment is a deleterious complication of bacterial infections that is difficult to treat or prevent. Listeria monocytogenes (Lm) is a neuroinvasive bacterial pathogen and commonly used model organism for studying immune responses to infection. Antibiotic-treated mice that survive systemic Lm infection have increased numbers of CD8⁺ and CD4⁺ T-lymphocytes in the brain that include tissue resident memory (T_RM) T cells, but post-infectious cognitive decline has not been demonstrated. We hypothesized that Lm infection would trigger cognitive decline in accord with increased numbers of recruited leukocytes.

Methods

Male C57BL/6J mice (age 8 wks) were injected with neuroinvasive Lm 10403s, non-neuroinvasive Δhly mutants, or sterile saline. All mice received antibiotics 2-16d post-injection (p.i.) and underwent cognitive testing 1 month (mo) or 4 mo p.i. using the Noldus PhenoTyper with Cognition Wall, a food reward-based discrimination procedure using automated home cage based observation and monitoring. After cognitive testing, brain leukocytes were quantified by flow cytometry.

Results

Changes suggesting cognitive decline were observed 1 mo p.i. in both groups of infected mice compared with uninfected controls, but were more widespread and significantly worse 4 mo p.i. and most notably after Lm 10403s. Impairments were observed in learning, extinction of prior learning and distance moved. Infection with Lm 10403s, but not Δhly Lm, significantly increased numbers of CD8⁺ and CD4⁺ T-lymphocytes, including populations expressing CD69 and T_RM cells, 1 mo p.i. Numbers of CD8⁺, CD69⁺CD8⁺ T-lymphocytes and CD8⁺ T_RM remained elevated at 4 mo p.i. but numbers of CD4⁺ cells returned to homeostatic levels. Higher numbers of brain CD8⁺ T-lymphocytes showed the strongest correlations with reduced cognitive performance.

Conclusions

Systemic infection by neuroinvasive as well as non-neuroinvasive Lm triggers a progressive decline in cognitive impairment. Notably, the deficits are more profound after neuroinvasive infection that triggers long-term retention of CD8⁺ T-lymphocytes in the brain, than after non-neuroinvasive infection, which does not lead to retained cells in the brain. These results support the conclusion that systemic infections, particularly those that lead to brain leukocytosis trigger a progressive decline in cognitive function and implicate CD8⁺ T-lymphocytes, including CD8⁺T_RM in the etiology of this impairment.

Newly Designed Primers for the Sequencing of the inlA Gene of Lineage I and II Listeria monocytogenes Isolates

Listeria monocytogenes is a major human foodborne pathogen responsible for listeriosis. The virulence factor Internalin A (inlA) has a key role in the invasion of L. monocytogenes into the human intestinal epithelium, and the presence of premature stop-codons (PMSC) mutations in the inlA gene sequence is correlated with attenuated virulence. The inlA sequencing process is carried out by dividing the gene into three sections which are then reassembled to obtain the full gene. The primers available however were only able to entirely amplify the lineage II isolates. In this study, we present a set of new primers which allow inlA sequencing of isolates belonging to both lineages, since lineage I isolates are the ones most frequently associated to clinical cases. Using newly designed primers, we assessed the presence of inlA PMSCs in food, food processing environments and clinical isolates.

Brainstem abscesses caused by Listeria monocytogenes: A case report

BACKGROUND

Intracranial Listeria infections are common in newborns and immunocompromised individuals, but brainstem abscesses are rare.

CASE SUMMARY

We report a rare case of brainstem abscesses caused by Listeria monocytogenes in a previously healthy adult patient. The patient’s magnetic resonance imaging examination showed multiple brain abscesses, and his second cerebrospinal fluid culture test indicated the presence of Listeria monocytogenes. Despite early empirical therapy, the patient’s condition progressively deteriorated. Because the patient's abscesses were located in the brainstem and multiple lobes, surgery was not possible. The patient died 40 d after admission.

CONCLUSION

This case highlights the importance of rational clinical use of drugs to avoid potentially serious infectious complications.

Retrospective Investigation of the Whole Genome of the Hypovirulent Listeria monocytogenes Strain of ST201, CC69, Lineage III, Isolated from a Piglet with Fatal Neurolisteriosis

Listeria monocytogenes (Lm), the causative agent for both human and animal listeriosis, is considered to be a rare but potentially fatal foodborne pathogen. While Lm strains associated with current cases of human listeriosis are now being intensely investigated, our knowledge of this microorganism which has caused listerial infection in the past is still extremely limited. The objective of this study was a retrospective whole-genome sequence analysis of the Lm collection strain, 4/52-1953, isolated in the middle of the 20th century from a piglet with listerial neuroinfection. The multi-locus sequence typing (MLST) analysis based on seven housekeeping genes (abcZ, bglA, cat, dapE, dat, ldh, and lhkA) showed that the Lm strain 4/52-1953 was assigned to the sequence type 201 (ST201), clonal complex 69 (CC69), and phylogenetic lineage III. The strain 4/52-1953, similarly to other ST201 strains, probably originated from the ST9, CC69 via ST157. At least eight different STs, ST69, ST72, ST130, ST136, ST148, ST469, ST769, and ST202, were identified as the descendants of the first generation and a single one, ST2290, was proved to be the descendant of the second generation. Among them there were strains either associated with some sporadic cases of human and animal listerial infection in the course of more than 60 years worldwide or isolated from food samples, fish and dairy products, or migratory birds. Phylogenetic analysis based on whole genomes of all the Lm strains available in the NCBI GenBank (n = 256) demonstrated that the strain 4/52-1953 belonged to minor Cluster I, represented by lineage III only, while two other major Clusters, II and III, were formed by lineages I and II. In the genome of the strain 4/52-1953, 41 virulence-associated genes, including the Listeria pathogenicity island 1 (LIPI-1), and LIPI-2 represented by two internalin genes, the inlA and inlB genes, and five genes related to antibiotic resistance, were found. These findings can help to make the emergence of both hyper- and hypovirulent variants, including those bearing antibiotic resistance genes, more visible and aid the aims of molecular epidemiology as well.

inlF Enhances Listeria monocytogenes Early-Stage Infection by Inhibiting the Inflammatory Response

The internalin family proteins, which carry the leucine repeat region structural motif, play diverse roles in Listeria monocytogenes (Lm) infection and pathogenesis. Although Internalin F, encoded by inlF, was identified more than 20 years ago, its role in the Lm anti-inflammatory response remains unknown. Lm serotype 4b isolates are associated with the majority of listeriosis outbreaks, but the function of InlF in these strains is not fully understood. In this study, we aimed to elucidate the role of inlF in modulating the inflammatory response and pathogenesis of the 4b strain Lm NTSN. Strikingly, although inlF was highly expressed at the transcriptional level during infection of five non-phagocytic cell types, it was not involved in adherence or invasion. Conversely, inlF did contributed to Lm adhesion and invasion of macrophages, and dramatically suppressed the expression of pro-inflammatory cytokines interleukin (IL)-1β and tumor necrosis factor (TNF-α). Consistent with the in vitro results, during Lm infection mice, inlF significantly inhibited the expression of IL-1β and IL-6 in the spleen, as well as IL-1β, IL-6, and TNF-α in the liver. More importantly, inlF contributed to Lm colonization in the spleen, liver, and ileum during the early stage of mouse infection via intragastric administration, inducing severe inflammatory injury and histopathologic changes in the late stage. To our knowledge, this is the first report to demonstrate that inlF mediates the inhibition of the pro-inflammatory response and contributes to the colonization and survival of Lm during the early stage of infection in mice. Our research partly explains the high pathogenicity of serovar 4b strains and will lead to new insights into the pathogenesis and immune evasion of Lm.

Listeria monocytogenes at the interface between ruminants and humans: A comparative pathology and pathogenesis review

The bacterium Listeria monocytogenes (Lm) is widely distributed in the environment as a saprophyte, but may turn into a lethal intracellular pathogen upon ingestion. Invasive infections occur in numerous species worldwide, but most commonly in humans and farmed ruminants, and manifest as distinct forms. Of those, neuroinfection is remarkably threatening due to its high mortality. Lm is widely studied not only as a pathogen but also as an essential model for intracellular infections and host-pathogen interactions. Many aspects of its ecology and pathogenesis, however, remain unclear and are rarely addressed in its natural hosts. This review highlights the heterogeneity and adaptability of Lm by summarizing its association with the environment, farm animals, and disease. It also provides current knowledge on key features of the pathology and (molecular) pathogenesis of various listeriosis forms in naturally susceptible species with a special focus on ruminants and on the neuroinvasive form of the disease. Moreover, knowledge gaps on pathomechanisms of listerial infections and relevant unexplored topics in Lm pathogenesis research are highlighted.

Investigation of brain mast cells in ovine encephalitic listeriosis

Mast cells in the brain are associated with increased inflammation during the acute period following exposure to infection; these cells are important for destroying the infectious agents. We investigated the relation between histopathological lesions and mast cells in sheep brains infected with Listeria. Pons and medulla regions from 17 infected and eight normal sheep brains were examined. Microabscesses and perivascular infiltration were assessed for histopathology. Mast cells were identified using toluidine blue and Listeria monocytogenes were investigated immunohistochemically. We found a significant increase in mast cells in infected sheep brains that was related directly to the extent of brain lesions. A strong correlation was found between mast cells and microabscess formation. A correlation between bacteria level and brain lesions also was observed, but not between bacteria level and mast cells. Our findings indicate that mast cells are increased following Listeria infection in sheep in proportion to the severity of brain lesions; the increase may contribute to acute inflammatory reactions and also may destroy bacteria directly.

Genome Sequences of Neurotropic Lineage III Listeria monocytogenes Isolates UKVDL9 and 2010L-2198

We report the whole-genome sequence of Listeria monocytogenes UKVDL9 and an edited draft genome sequence of L. monocytogenes 2010L-2198. Both are neurotropic lineage III strains; UKVDL9 was isolated from a sheep brain, and 2010L-2198 was isolated from a human subject with rhombencephalitis.

We report the whole-genome sequence of Listeria monocytogenes UKVDL9 and an edited draft genome sequence of L. monocytogenes 2010L-2198. Both are neurotropic lineage III strains; UKVDL9 was isolated from a sheep brain, and 2010L-2198 was isolated from a human subject with rhombencephalitis.