Evaluation of transcription levels of inlA, inlB, hly, bsh and prfA genes in Listeria monocytogenes strains using quantitative reverse-transcription PCR and ability of invasion into human CaCo-2 cells

Clostridiales in the Gut Against Listeria monocytogenes Infection Through Growth Inhibition

Listeria monocytogenes (Lm) mainly infect pregnant women, children, the elderly, and other populations with low immunity causing septicemia and meningitis. Healthy people can tolerate higher doses of Lm and only cause gastrointestinal symptoms such as abdominal pain and diarrhea after infection. Compared to the above population, healthy people have a richer and more diverse gut microbiota. In this study, we show that the microbiota in the large intestine and the feces of mice can significantly inhibit the growth of Lm compared to the microbiota in the small intestine. Bacteria larger than 1 μm in the gut microbiota play an important role in inhibiting Lm growth. 16s rRNA sequencing results show that these bacteria are mainly composed of Clostridiales under the phylum Firmicutes, including Ruminiclostridium, Butyricicoccus, Lachnoclostridium, Roseburia, Coprooccus, and Blautia. Thus, we demonstrate that there are some potential functional bacteria in the gut microbiota that can increase resistance against Lm.

Natural Isoforms of Listeria monocytogenes Virulence Factor Inlb Differ in c-Met Binding Efficiency and Differently Affect Uptake and Survival Listeria in Macrophage

Listeria monocytogenes virulence factor InlB specifically interacts with the receptors c-Met and gC1q-R. Both receptors are present in non-professional and professional phagocytes, including macrophages. Phylogenetically defined InlB isoforms differently support invasion into non-professional phagocytes. This work deals with the effects of InlB isoforms on L. monocytogenes uptake and intracellular proliferation in human macrophages. Three isoforms of the receptor binding domain (idInlB) were derived from phylogenetically distinct L. monocytogenes strains belonging to the highly virulent CC1 (idInlB_CC1), medium-virulence CC7 (idInlB_CC7), and low-virulence CC9 (idInlB_CC9) clonal complexes. The constant dissociation increased in the order idInlB_CC1 << idInlB_CC7 < idInlB_CC9 for interactions with c-Met, and idInlB_CC1 ≈ idInlB_CC7 < idInlB_CC9 for interactions with gC1q-R. The comparison of uptake and intracellular proliferation of isogenic recombinant strains which expressed full-length InlBs revealed that the strain expressing idInlB_CC1 proliferated in macrophages twice as efficiently as other strains. Macrophage pretreatment with idInlB_CC1 followed by recombinant L. monocytogenes infection disturbed macrophage functions decreasing pathogen uptake and improving its intracellular multiplication. Similar pretreatment with idInlB_CC7 decreased bacterial uptake but also impaired intracellular multiplication. The obtained results demonstrated that InlB impaired macrophage functions in an idInlB isoform-dependent manner. These data suggest a novel InlB function in L. monocytogenes virulence.

Fecal microbiota transplantation reduces mouse mortality from Listeria monocytogenes infection

Listeria monocytogenes (Lm) is a food bacterium with strong pathogenicity which causes infections via the gastrointestinal tract. Mechanisms by which gut microbiota (GM) resist microbial infections have received little attention. Eight-week-old mice were orally inoculated with wild-type Lm EGD-e and fecal microbiota transplantation (FMT) employed. GM richness and diversity of infected mice changed rapidly within 24h. Firmicutes class decreased and Bacteroidetes, Tenericutes and Ruminococcaceae increased significantly. Coprococcus, Blautia and Eubacterium also increased on the 3rd day post-infection. Moreover, GM transplanted from healthy mice reduced mortality of infected mice by approximately 32%. FMT treatment decreased production of TNFα, IFN-γ, IL-1β and IL-6 relative to PBS treatment. In summary, FMT has potential as a treatment against Lm infection and may be used for bacterial resistance management. Further work is required to elucidate the key GM effector molecules.

TMT-Based Quantitative Proteomic Analysis of Intestinal Organoids Infected by Listeria monocytogenes Strains with Different Virulence

L. monocytogenes, consisting of 13 serotypes, is an opportunistic food-borne pathogen that causes different host reactions depending on its serotypes. In this study, highly toxic L. monocytogenes 10403s resulted in more severe infections and lower survival rates. Additionally, to investigate the remodeling of the host proteome by strains exhibiting differential toxicity, the cellular protein responses of intestinal organoids were analyzed using tandem mass tag (TMT) labeling and high-performance liquid chromatography−mass spectrometry. The virulent strain 10403s caused 102 up-regulated and 52 down-regulated proteins, while the low virulent strain M7 caused 188 up-regulated and 25 down-regulated proteins. Based on the analysis of gene ontology (GO) and KEGG databases, the expressions of differential proteins in organoids infected by L. monocytogenes 10403s (virulent strain) or M7 (low virulent strain) were involved in regulating essential processes such as the biological metabolism, the energy metabolism, and immune system processes. The results showed that the immune system process, as the primary host defense response to L. monocytogenes, comprised five pathways, including ECM−receptor interaction, the complement and coagulation cascades, HIF-1, ferroptosis, and NOD-like receptor signaling pathways. As for the L. monocytogenes 10403s vs. M7 group, the expression of differential proteins was involved in two pathways: systemic lupus erythematosus and transcriptional mis-regulation in cancer. All in all, these results revealed that L. monocytogenes strains with different toxicity induced similar biological functions and immune responses while having different regulations on differential proteins in the pathway.

The seasonality, steroid use, and lower ratio of neutrophil to lymphocyte associated with bacteremia of Listeria monocytogenes in Japan from 2010 to 2019: a case-control study

Background

Despite having a high mortality rate, Asian studies about the characteristics of adult listeriosis are limited. We investigated the incidence of listeriosis per admissions, associated factors, and rate of mortality in listeriosis, compared with non-listeriosis.

Methods

We recorded the incidence of listeriosis per 10,000 admissions and conducted a case–control study from January 1, 2010, to December 31, 2019, at Tokyo Medical University Hospital (TMUH) in Japan. Cases were defined as adult with listeriosis that was bacteremia due to L. monocytogenes. Controls, defined as adult with non-listeriosis bacteremia due to other pathogens, were matched by age and clinical department to cases. We analyzed differences in seasonality, including warm season (defined as the period from May to October), medication including steroids, laboratory findings, and mortality. The odds ratio and p value between the cases group and control group were calculated using a chi-square test and Fisher’s exact test.

Results

The incidence of listeriosis per 10,000 admissions to TMUH was 0.51. Eleven patients, excluding one neonate, were included in the case group. Twenty-six patients, excluding one patient because of contamination and one patient because of insufficient medical record, were included in the control group. Listeriosis onset was associated with the warm season (90.9% vs. 53.8%; p = 0.033), steroid use (54.5% vs. 19.2%; p = 0.042), and a lower ratio of neutrophils to lymphocytes (9.46 vs. 18.44; p = 0.015). The 30-day mortality rate of listeriosis was similar to non-listeriosis (18.3% vs. 19.2%; p = 0.619).

Conclusion

The incidence of listeriosis per admissions in this study was similar to that in other Asian countries. Factors associated with listeriosis were the warm season, steroid use, and a lower ratio of neutrophils to lymphocytes. Additionally, the 30-day mortality rate was similarly high in both the listeriosis and non-listeriosis groups.

Genetic Factors Affect the Survival and Behaviors of Selected Bacteria during Antimicrobial Blue Light Treatment

Antimicrobial resistance is a global, mounting and dynamic issue that poses an immediate threat to human, animal, and environmental health. Among the alternative antimicrobial treatments proposed to reduce the external use of antibiotics is electromagnetic radiation, such as blue light. The prevailing mechanistic model is that blue light can be absorbed by endogenous porphyrins within the bacterial cell, inducing the production of reactive oxygen species, which subsequently inflict oxidative damages upon different cellular components. Nevertheless, it is unclear whether other mechanisms are involved, particularly those that can affect the efficacy of antimicrobial blue light treatments. In this review, we summarize evidence of inherent factors that may confer protection to a selected group of bacteria against blue light-induced oxidative damages or modulate the physiological characteristics of the treated bacteria, such as virulence and motility. These include descriptions of three major photoreceptors in bacteria, chemoreceptors, SOS-dependent DNA repair and non-SOS protective mechanisms. Future directions are also provided to assist with research efforts to increase the efficacy of antimicrobial blue light and to minimize the development of blue light-tolerant phenotypes.

Listeria monocytogenes Establishes Commensalism in Germ-Free Mice Through the Reversible Downregulation of Virulence Gene Expression

The intestine harbors a complex community of bacterial species collectively known as commensal microbiota. Specific species of resident bacteria, as known as pathobiont, have pathogenic potential and can induce apparent damage to the host and intestinal inflammation in a certain condition. However, the host immune factors that permit its commensalism under steady state conditions are not clearly understood. Here, we studied the gut fitness of Listeria monocytogenes by using germ-free (GF) mice orally infected with this food-borne pathogen. L. monocytogenes persistently exists in the gut of GF mice without inducing chronic immunopathology. L. monocytogenes at the late phase of infection is not capable of infiltrating through the intestinal barrier. L. monocytogenes established the commensalism through the reversible down regulation of virulence gene expression. CD8⁺ T cells were found to be sufficient for the commensalism of L. monocytogenes. CD8⁺ T cells responding to L. monocytogenes contributed to the down-regulation of virulence gene expression. Our data provide important insights into the host-microbe interaction and have implications for developing therapeutics against immune disorders induced by intestinal pathogens or pathobionts.

Multiplex PCR for the Identification of Pathogenic Listeria in Flammulina velutipes Plant Based on Novel Specific Targets Revealed by Pan-Genome Analysis

Listeria spp. is an important foodborne disease agent, often found in the fresh mushroom (Flammulina velutipes) and its production environment. The aim of this study was to develop multiplex PCR for rapid identification of Listeria monocytogenes and Listeria ivanovii, and nonpathogenic Listeria in F. velutipes plants. Pan-genome analysis was first used to identify five novel Listeria-specific targets: one for the Listeria genus, one for L. monocytogenes, and three for L. ivanovii. Primers for the novel targets were highly specific in individual reactions. The detection limits were 10³-10⁴ CFU/mL, meeting the requirements of molecular detection. A mPCR assay for the identification of pathogenic Listeria, with primers targeting the novel genes specific for Listeria genus (LMOSLCC2755_0944), L. monocytogenes (LMOSLCC2755_0090), and L. ivanovii (queT_1) was then designed. The assay specificity was robustly verified by analyzing nonpathogenic Listeria and non-Listeria spp. strains. The determined detection limits were 2.0 × 10³ CFU/mL for L. monocytogenes and 3.4 × 10³ CFU/mL for L. ivanovii, for pure culture analysis. Further, the assay detected 7.6 × 10⁴ to 7.6 × 10⁰ CFU/10 g of pathogenic Listeria spiked into F. velutipes samples following 4-12 h enrichment. The assay feasibility was evaluated by comparing with a traditional culture-based method, by analyzing 129 samples collected from different F. velutipes plants. The prevalence of Listeria spp. and L. monocytogenes was 58.1% and 41.1%, respectively. The calculated κ factors for Listeria spp., L. monocytogenes, and L. ivanovii were 0.97, 0.97, and 1, respectively. The results of the novel mPCR assay were highly consistent with those of the culture-based method. The new assay thus will allow rapid, specific, and accurate detection and monitoring of pathogenic Listeria in food and its production environment.

Characterisation of Listeria monocytogenes isolates from cattle using a bovine caruncular epithelial cell model

Listeria monocytogenes is an important foodborne pathogen in human and veterinary health, causing significant morbidity and mortality including abortion. It has a particular tropism for the gravid uterus, however, the route of infection in reproductive tissues of ruminants (i.e. placentome), is much less clear. In this study, we aimed to investigate a bovine caruncular epithelial cell (BCEC) line as a model for L. monocytogenes infection of the bovine reproductive tract. The BCEC infection model was used to assess the ability of 14 different L. monocytogenes isolates to infect these cells. Lysozyme sensitivity and bacterial survival in 580 μg lysozyme/ml correlated with attenuated ability to proliferate in BCEC (p = 0.004 and p = 0.02, respectively). Four isolates were significantly attenuated compared to the control strain 10403S. One of these strains (AR008) showed evidence of compromised cell wall leading to increased sensitivity to ß-lactam antibiotics, and another (7644) had compromised cell membrane integrity leading to increased sensitivity to cationic peptides. Whole genome sequencing followed by Multi Locus Sequence Type analysis identified that five invasive isolates had the same sequence type, ST59, despite originating from three different clinical conditions. Virulence gene analysis showed that the attenuated isolate LM4 was lacking two virulence genes (uhpT, virR) known to be involved in intracellular growth and virulence.

In conclusion, the BCEC model was able to differentiate between the infective potential of different isolates. Moreover, resistance to lysozyme correlated with the ability to invade and replicate within BCEC, suggesting co-selection for surviving challenging environments as the abomasum.

Characterization of internalin genes in Listeria monocytogenes from food and humans, and their association with the invasion of Caco-2 cells

Background

Internalins are surface proteins that are utilized by Listeria monocytogenes to facilitate its invasion into human intestinal epithelial cells. The expression of a full-length InlA is one of essential virulence factors for L. monocytogenes to cross the intestinal barrier in order to invade epithelial cells.

Results

In this study, the gene sequences of inlA in 120 L. monocytogenes isolates from food (n = 107) and humans (n = 13) were analyzed. Premature stop codon (PMSC) mutations in inlA were identified in 51 isolates (50 from food and 1 from human). Six mutation types of PMSCs were identified. Among the 51 isolates with PMSCs in inlA, there were 44 serogroup 1/2c, 3c isolates from food, of which seven belonged to serogroups 1/2a, 3a. A total of 153,382 SNPs in 2247 core genes from 42 genomes were identified and used to construct a phylogenetic tree. Serotype 1/2c isolates with inlA PMSC mutations were grouped together. Cell culture studies on 21 isolates showed that the invasion to Caco-2 cells was significantly reduced among isolates with inlA PMSC mutations compared to those without PMSC mutations (P < 0.01). The PMSC mutations in inlA correlated with the inability of the L. monocytogenes isolates to invade Caco-2 cells (Pearson’s coefficient 0.927, P < 0.01).

Conclusion

Overall, the study has revealed the reduced ability of L. monocytogenes to invade human intestinal epithelial cells in vitro was linked to the presence of PMSC mutations in inlA. Isolates with PMSC mutations shared the same genomic characteristics indicating the genetic basis on the potential virulence of L. monocytogenes invasion.

Electronic supplementary material

The online version of this article (10.1186/s13099-019-0307-8) contains supplementary material, which is available to authorized users.

High resolution melting analysis for the characterization of lineage II Listeria monocytogenes serovars 1/2a and 1/2c based on single nucleotide polymorphisms identification within the Listeria Pathogenicity Island-1 and inlAB operon: a novel approach for epidemiological surveillance

AIMS

A high resolution melting (HRM) assay was developed for characterizing lineage II Listeria monocytogenes based on the amplification and the melting profiles analysis of 81 fragments targeting the region from the prs to ldh loci, including the Listeria Pathogenicity Island-1 (LIPI-1) genes and the inlAB operon.

METHODS AND RESULTS

Real-time PCR and HRM protocols were standardized using 10 replicate assays from L. monocytogenes EGD-e reference strain (serovar 1/2a). Twenty wild-type isolates of serovar 1/2a and two of serovar 1/2c were tested, and differences between EGD-e strain and the wild-type isolates were defined if the melting temperature (Tm ) of an amplicon was not within the lower and the upper limits calculated from replicate testing on EGD-e. The analysis revealed 17 and 19 HRM profiles with respect to prs/LIPI-1/ldh and inlAB target regions (Simpson's Index of Diversity 0·979 and 0·983) respectively. The 1/2c cultures showed 98·1% similarity to melting characteristics with EGD-e, whilst 1/2a isolates had the greatest heterogeneity that was related to inlA, inlB and actA genes. Sequencing of amplicons generating different Tm values from EGD-e confirmed the presence of point mutations.

CONCLUSIONS

This method was useful for L. monocytogenes subtyping based on single nucleotide polymorphisms detection through the melting behaviour analysis of main virulence genes.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study underlines the effectiveness of HRM in differentiating L. monocytogenes strains with high discriminatory power, thus rendering it useful for epidemiological surveillance.

Antimicrobial resistance and genotypic characteristics of Listeria monocytogenes isolated from food in Poland

The aim of the study was to determine antimicrobial resistance and genotypic characteristics of L. monocytogenes isolated from food of animal origin from different parts of Poland during years 2013-2016. A total of 146 isolates were tested using a microbroth dilution method, whereas virulence genes and molecular serogroups were identified by PCR. Pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) methods were used to analyze the genotypic relationship of the strains. Altogether, 102 pulsotypes grouped into 7 clusters and 24 sequence types, including 3 new types, were identified. Most of the strains clustered into individual patterns were originated from different food products and were isolated in different geographical regions at various time. L. monocytogenes was mostly resistant to oxacilin (90.4% strains), clindamycin (54.1%) and ceftriaxone (49.3%). A multiresistance patterns, mainly to ceftriaxone, oxacillin together with other antimicrobials, were observed among 27.4% strains. Antimicrobial resistance and presence of virulence genes suggest that food of animal origin contaminated with L. monocytogenes may present a risk for public health.

Listeria monocytogenes sequence type 1 is predominant in ruminant rhombencephalitis

Listeria (L.) monocytogenes is an opportunistic pathogen causing life-threatening infections in diverse mammalian species including humans and ruminants. As little is known on the link between strains and clinicopathological phenotypes, we studied potential strain-associated virulence and organ tropism in L. monocytogenes isolates from well-defined ruminant cases of clinical infections and the farm environment. The phylogeny of isolates and their virulence-associated genes were analyzed by multilocus sequence typing (MLST) and sequence analysis of virulence-associated genes. Additionally, a panel of representative isolates was subjected to in vitro infection assays. Our data suggest the environmental exposure of ruminants to a broad range of strains and yet the strong association of sequence type (ST) 1 from clonal complex (CC) 1 with rhombencephalitis, suggesting increased neurotropism of ST1 in ruminants, which is possibly related to its hypervirulence. This study emphasizes the importance of considering clonal background of L. monocytogenes isolates in surveillance, epidemiological investigation and disease control.