Evaluation of Caco-2 cells response to Listeria monocytogenes virulence factors by RT-PCR

Role of ethanolamine utilization and bacterial microcompartment formation in Listeria monocytogenes intracellular infection

Ethanolamine (EA) affects the colonization and pathogenicity of certain human bacterial pathogens in the gastrointestinal tract. However, EA can also affect the intracellular survival and replication of host cell invasive bacteria such as Listeria monocytogenes (LMO) and Salmonella enterica serovar Typhimurium (S. Typhimurium). The EA utilization (eut) genes can be categorized as regulatory, enzymatic, or structural, and previous work in LMO showed that loss of genes encoding functions for the enzymatic breakdown of EA inhibited LMO intracellular replication. In this work, we sought to further characterize the role of EA utilization during LMO infection of host cells. Unlike what was previously observed for S. Typhimurium, in LMO, an EA regulator mutant (ΔeutV) was equally deficient in intracellular replication compared to an EA metabolism mutant (ΔeutB), and this was consistent across Caco-2, RAW 264.7, and THP-1 cell lines. The structural genes encode proteins that self-assemble into bacterial microcompartments (BMCs) that encase the enzymes necessary for EA metabolism. For the first time, native EUT BMCs were fluorescently tagged, and EUT BMC formation was observed in vitro and in vivo. Interestingly, BMC formation was observed in bacteria infecting Caco-2 cells, but not the macrophage cell lines. Finally, the cellular immune response of Caco-2 cells to infection with eut mutants was examined, and it was discovered that ΔeutB and ΔeutV mutants similarly elevated the expression of inflammatory cytokines. In conclusion, EA sensing and utilization during LMO intracellular infection are important for optimal LMO replication and immune evasion but are not always concomitant with BMC formation.IMPORTANCEListeria monocytogenes (LMO) is a bacterial pathogen that can cause severe disease in immunocompromised individuals when consumed in contaminated food. It can replicate inside of mammalian cells, escaping detection by the immune system. Therefore, understanding the features of this human pathogen that contribute to its infectiousness and intracellular lifestyle is important. In this work we demonstrate that genes encoding both regulators and enzymes of EA metabolism are important for optimal growth inside mammalian cells. Moreover, the formation of specialized compartments to enable EA metabolism were visualized by tagging with a fluorescent protein and found to form when LMO infects some mammalian cell types, but not others. Interestingly, the formation of the compartments was associated with features consistent with an early stage of the intracellular infection. By characterizing bacterial metabolic pathways that contribute to survival in host environments, we hope to positively impact knowledge and facilitate new treatment strategies.

Role of Ethanolamine Utilization and Bacterial Microcompartment Formation in Listeria monocytogenes Intracellular Infection

Ethanolamine (EA) affects the colonization and pathogenicity of certain human bacterial pathogens in the gastrointestinal tract. However, EA can also affect the intracellular survival and replication of host-cell invasive bacteria such as Listeria monocytogenes (LMO) and Salmonella enterica serovar Typhimurium ( S. Typhimurium). The EA utilization ( eut) genes can be categorized as regulatory, enzymatic, or structural, and previous work in LMO showed that loss of genes encoding functions for the enzymatic breakdown of EA inhibited LMO intracellular replication. In this work, we sought to further characterize the role of EA utilization during LMO infection of host cells. Unlike what was previously observed for S. Typhimurium, in LMO, an EA regulator mutant ( ΔeutV) was equally deficient in intracellular replication compared to an EA metabolism mutant ( ΔeutB ), and this was consistent across Caco-2, RAW 264.7 and THP-1 cell lines. The structural genes encode proteins that self-assemble into bacterial microcompartments (BMCs) that encase the enzymes necessary for EA metabolism. For the first time, native EUT BMCs were fluorescently tagged, and EUT BMC formation was observed in vitro, and in vivo. Interestingly, BMC formation was observed in bacteria infecting Caco-2 cells, but not the macrophage cell lines. Finally, the cellular immune response of Caco-2 cells to infection with eut mutants was examined, and it was discovered that ΔeutB and ΔeutV mutants similarly elevated the expression of inflammatory cytokines. In conclusion, EA sensing and utilization during LMO intracellular infection are important for optimal LMO replication and immune evasion but are not always concomitant with BMC formation.

Bacteriophage targeting microbiota alleviates non-alcoholic fatty liver disease induced by high alcohol-producing Klebsiella pneumoniae

Our previous studies have shown that high alcohol-producing Klebsiella pneumoniae (HiAlc Kpn) in the intestinal microbiome could be one of the causes of non-alcoholic fatty liver disease (NAFLD). Considering antimicrobial resistance of K. pneumoniae and dysbacteriosis caused by antibiotics, phage therapy might have potential in treatment of HiAlc Kpn-induced NAFLD, because of the specificity targeting the bacteria. Here, we clarified the effectiveness of phage therapy in male mice with HiAlc Kpn-induced steatohepatitis. Comprehensive investigations including transcriptomes and metabolomes revealed that treatment with HiAlc Kpn-specific phage was able to alleviate steatohepatitis caused by HiAlc Kpn, including hepatic dysfunction and expression of cytokines and lipogenic genes. In contrast, such treatment did not cause significantly pathological changes, either in functions of liver and kidney, or in components of gut microbiota. In addition to reducing alcohol attack, phage therapy also regulated inflammation, and lipid and carbohydrate metabolism. Our data suggest that phage therapy targeting gut microbiota is an alternative to antibiotics, with potential efficacy and safety, at least in HiAlc Kpn-caused NAFLD.

Systematic identification of a panel of strong promoter regions from Listeria monocytogenes for fine-tuning gene expression

BACKGROUND

Attenuated Listeria monocytogenes (Lm) has been widely used as a vaccine vector in the prevention and treatment of pathogen infection and tumor diseases. In addition, previous studies have proved that the attenuated Lm can protect zebrafish from Vibrio infections, indicating that the attenuated Lm has a good application prospect in the field of aquatic vaccines. However, the limitation mainly lies in the lack of a set of well-characterized natural promoters for the expression of target antigens in attenuated Lm.

RESULTS

In our study, candidate strong promoters were identified through RNA-seq analysis, and characterized in Lm through enhanced green fluorescent protein (EGFP). Nine native promoters that showed stronger activities than that of the known strong promoter P36 under two tested temperatures (28 and 37 °C) were selected from the set, and P29 with the highest activity was 24-fold greater than P36. Furthermore, we demonstrated that P29 could initiate EGFP expression in ZF4 cells and zebrafish embryos.

CONCLUSIONS

This well-characterized promoter library can be used to fine-tune the expression of different proteins in Lm. The availability of a well-characterized promoter toolbox of Lm is essential for the analysis of yield increase for biotechnology applications.

Protection of surface layer protein from Enterococcus faecium WEFA23 against Listeria monocytogenes CMCC54007 infection by modulating intestinal permeability and immunity

Enterococcus faecium WEFA23 was previously found effectively against adherence and colonization of Listeria monocytogenes CMCC54007, which might be closely related to its surface layer protein (SLP). In this study, the protective of SLP of E. faecium WEFA23 against infection of L. monocytogenes CMCC54007 was systemically investigated. In vitro assay showed that SLP actively inhibited L. monocytogenes internalization into Caco-2 cell line, with decreasing mRNA level of pro-inflammation cytokines and virulence factors and restoring destroyed intestinal barrier. In vivo assay through excluding SLP of E. faecium WEFA23 by 5 M LiCl represented that SLP increased body weight, reduced mortality and cell counts of L. monocytogenes CMCC54007 in tissues of mice. Further researches showed that SLP protected against L. monocytogenes CMCC54007 infection by modulation of intestinal permeability and immunity, namely, it decreased fluorescein isothiocyanate (FITC)-Dextran in serum, ameliorated destroyed colon structure, and increased number of goblet cells and protein level of TJ protein (Claudin-1, Occludin, and ZO-1) in colon. For immunity, SLP decreased number of CD4⁺ and CD8⁺ T cells in liver, mRNA level, and content of pro-inflammatory factors IL-6, IL-1β, IFN-γ ,TNF-α, and NO, and restored the structure of liver and spleen. Key Points•SLP of E. faecium inhibited L. monocytogenes internalization and colonization•SLP of E. faecium ameliorated host intestinal barrier dysfunction•SLP of E. faecium decreased pro-inflammatory cytokines and cells.

Assessment of Internalin A Gene Sequences and Cell Adhesion and Invasion Capacity of Listeria monocytogenes Strains Isolated from Foods of Animal and Related Origins

Listeria monocytogenes is a foodborne pathogen of global relevance that causes outbreaks and sporadic cases of listeriosis, acquired through the consumption of contaminated products, including milk or meat products and ready-to-eat meat products subjected to intensive handling. The objective of the present study was to classify L. monocytogenes isolated from various food-related sources in the Federal District of Brazil and surrounding areas to sequence internalin A (inlA) genes from these isolates and assess their adhesion and invasion capacity using Caco-2 cells. In addition, 15 were classified as group I, 3 as group II, and 7 classified as group IV. Premature stop codons (PMSCs) at the nucleotide position 976 (GAA→TAA) of the inlA gene were identified in 5 of the 25 isolates. Adhesion and invasion tests in Caco-2 cells showed that all the isolates were capable of adhesion and cellular invasion, with isolates containing PMSCs exhibiting on average higher invasion capacity than those without PMSCs (p = 0.041) and a median of adhesion very distinctive from those without stop codons. These results are the first report of PMSCs in the inlA gene of L. monocytogenes from the Federal District of Brazil and Brazil.

Immunological evaluation of virulence-deficient Listeria monocytogenes strains in C57BL/6 mice

Attenuated Listeria monocytogenes (L. monocytogenes), which has unique advantages in presenting foreign antigens, was widely used in tumor immunotherapy research. As a live vaccine vector, attenuated L. monocytogenes was required to not only have certain invasiveness but also ensure safety, while the lack of different virulence factors may cause L. monocytogenes to show different safety and invasiveness. To evaluate the potential of virulence-deficient L. monocytogenes strains as a vaccine vector, four mutant strains EGD-eΔactA, EGD-eΔactA/inlB, EGD-eΔhly, and EGD-eΔprfA were used to infect C57BL/6 mice for determining related immune indexes. Compared with EGD-e, mutant strains showed significantly decreased invasion in C57BL/6 mice and caused relatively minor damage to spleen and liver. However, EGD-eΔactA and EGD-eΔactA/inlB were superior to EGD-eΔhly and EGD-eΔprfA in the comprehensive evaluation of inflammatory factor transcription level, immune cell differentiation and antibody level, which proved that they have a stronger adjuvant effect as a vaccine vector.

Pathogenic Biohacking: Induction, Modulation and Subversion of Host Transcriptional Responses by Listeria monocytogenes

During infection, the foodborne bacterial pathogen Listeria monocytogenes dynamically influences the gene expression profile of host cells. Infection-induced transcriptional changes are a typical feature of the host-response to bacteria and contribute to the activation of protective genes such as inflammatory cytokines. However, by using specialized virulence factors, bacterial pathogens can target signaling pathways, transcription factors, and epigenetic mechanisms to alter host gene expression, thereby reprogramming the response to infection. Therefore, the transcriptional profile that is established in the host is delicately balanced between antibacterial responses and pathogenesis, where any change in host gene expression might significantly influence the outcome of infection. In this review, we discuss the known transcriptional and epigenetic processes that are engaged during Listeria monocytogenes infection, the virulence factors that can remodel them, and the impact these processes have on the outcome of infection.

Two Prevalent Listeria ivanovii subsp. ivanovii Clonal Strains With Different Virulence Exist in Wild Rodents and Pikas of China

Listeria ivanovii subsp. ivanovii is an intracellular bacterium distributed widely in nature, causing the listeriosis in ruminants and humans. Previous researches had isolated 116 strains of L. ivanovii subsp. ivanovii from wild rodents and pikas of different regions in China, and the predominant sequence types were ST1 and ST2. In this study, we first investigated the biological characteristics and virulence of these two clonal strains including motility, metabolism and virulence in cells and mouse model. The results demonstrated the ST1 strains exhibited motility, wide metabolic activity and hypervirulence, whereas the ST2 strains showed non-motility, relative lower metabolic activity and virulence. Considering the transmissible ability from wild rodents and pikas to ecological environment, the L. ivanovii subsp. ivanovii with potential pathogenicity to humans and ruminants should be monitored.

Modulatory effect of low-shear modeled microgravity on stress resistance, membrane lipid composition, virulence, and relevant gene expression in the food-borne pathogen Listeria monocytogenes

The present study investigated the influence of low-shear modeled microgravity (LSMMG) conditions on Listeria monocytogenes stress response (heat, cold, and acid), membrane fatty acid composition, and virulence potential as well as stress-/virulence-associated gene expression. The results showed that LSMMG-cultivated cells had lower survival rate and lower D-values under heat and acid stress conditions compared to cells grown under normal gravity (NG). Interestingly, the cold resistance was elevated in cells cultivated under LSMMG conditions when compared to NG conditions. A higher amount of anteiso-branched chain fatty acids and lower ratio of iso/anteiso were observed in LSMMG cultured cells, which would contribute to increased membrane fluidity. Under LSMMG conditions, upregulated expression of cold stress-related genes (cspA, cspB, and cspD) was noticed but no change in expression was observed for heat (dnaK, groES, clpC, clpP, and clpE) and acid stress-related genes (sigB). The LSMMG-grown cells showed inferior virulence capacity in terms of infection, cell cycle arrest, and apoptosis induction in Caco-2 cells compared to those grown under NG conditions. Approximately 3.65, 2.13, 4.02, and 2.65-fold downregulation of prfA, hly, inlA, and bsh genes, respectively, in LSMMG-cultured cells might be the reason for reduced virulence. In conclusion, these findings suggest that growth under LSMMG conditions stimulates alterations in L. monocytogenes stress/virulence response, perhaps due to changes in lipid composition and related genes expression.

Innate and Adaptive Immune Responses during Listeria monocytogenes Infection

It could be argued that we understand the immune response to infection with Listeria monocytogenes better than the immunity elicited by any other bacteria. L. monocytogenes are Gram-positive bacteria that are genetically tractable and easy to cultivate in vitro, and the mouse model of intravenous (i.v.) inoculation is highly reproducible. For these reasons, immunologists frequently use the mouse model of systemic listeriosis to dissect the mechanisms used by mammalian hosts to recognize and respond to infection. This article provides an overview of what we have learned over the past few decades and is divided into three sections: "Innate Immunity" describes how the host initially detects the presence of L. monocytogenes and characterizes the soluble and cellular responses that occur during the first few days postinfection; "Adaptive Immunity" discusses the exquisitely specific T cell response that mediates complete clearance of infection and immunological memory; "Use of Attenuated Listeria as a Vaccine Vector" highlights the ways that investigators have exploited our extensive knowledge of anti-Listeria immunity to develop cancer therapeutics.