Carvacrol prophylaxis improves clinical outcome and dampens apoptotic and pro-inflammatory immune responses upon Campylobacter jejuni infection of human microbiota-associated IL-10-/- mice

Incidence rates of human Campylobacter jejuni infections are progressively increasing globally. Since the risk for the development of post-infectious autoimmune diseases correlates with the severity of the preceding enteritis and campylobacteriosis treatment usually involves symptomatic measures, it is desirable to apply antibiotic-independent compounds to treat or even prevent disease. Given its health-promoting including anti-inflammatory properties carvacrol constitutes a promising candidate. This prompted us to test the disease-alleviating including immune-modulatory effects of carvacrol prophylaxis in acute murine campylobacteriosis. Therefore, human gut microbiota-associated IL-10-/- mice were orally challenged with synthetic carvacrol starting a week before C. jejuni infection and followed up until day 6 post-infection. Whereas carvacrol prophylaxis did neither affect gastrointestinal pathogen loads, nor the human commensal gut microbiota composition, it improved the clinical outcome of mice, attenuated colonic epithelial cell apoptosis, and dampened pro-inflammatory immune responses not only in the intestinal tract but also in extra-intestinal organs including the liver and the spleen. In conclusion, our preclinical placebo-controlled intervention study provides convincing evidence that oral carvacrol pretreatment constitutes a promising option to mitigate acute campylobacteriosis and in turn, to reduce the risk for post-infectious complications.

Nitric oxide signaling through three receptors regulates virulence, biofilm formation, and phenotypic heterogeneity of Legionella pneumophila

The causative agent of Legionnaires' disease, Legionella pneumophila, is an environmental bacterium, that replicates in macrophages, parasitizes amoeba, and forms biofilms. L. pneumophila employs the Legionella quorum sensing (Lqs) system and the transcription factor LvbR to control various bacterial traits, including virulence and biofilm architecture. LvbR negatively regulates the nitric oxide (NO) receptor Hnox1, linking quorum sensing to NO signaling. Here, we assessed the response of L. pneumophila to NO and investigated bacterial receptors underlying this process. Chemical NO donors, such as dipropylenetriamine (DPTA) NONOate and sodium nitroprusside (SNP), delayed and reduced the expression of the promoters for flagellin (PflaA) and the 6S small regulatory RNA (P6SRNA). Marker-less L. pneumophila mutant strains lacking individual (Hnox1, Hnox2, or NosP) or all three NO receptors (triple knockout, TKO) grew like the parental strain in media. However, in the TKO strain, the reduction of PflaA expression by DPTA NONOate was less pronounced, suggesting that the NO receptors are implicated in NO signaling. In the ΔnosP mutant, the lvbR promoter was upregulated, indicating that NosP negatively regulates LvbR. The single and triple NO receptor mutant strains were impaired for growth in phagocytes, and phenotypic heterogeneity of non-growing/growing bacteria in amoebae was regulated by the NO receptors. The single NO receptor and TKO mutant strains showed altered biofilm architecture and lack of response of biofilms to NO. In summary, we provide evidence that L. pneumophila regulates virulence, intracellular phenotypic heterogeneity, and biofilm formation through NO and three functionally non-redundant NO receptors, Hnox1, Hnox2, and NosP.

IMPORTANCE

The highly reactive diatomic gas molecule nitric oxide (NO) is produced by eukaryotes and bacteria to promote short-range and transient signaling within and between neighboring cells. Despite its importance as an inter-kingdom and intra-bacterial signaling molecule, the bacterial response and the underlying components of the signaling pathways are poorly characterized. The environmental bacterium Legionella pneumophila forms biofilms and replicates in protozoan and mammalian phagocytes. L. pneumophila harbors three putative NO receptors, one of which crosstalks with the Legionella quorum sensing (Lqs)-LvbR network to regulate various bacterial traits, including virulence and biofilm architecture. In this study, we used pharmacological, genetic, and cell biological approaches to assess the response of L. pneumophila to NO and to demonstrate that the putative NO receptors are implicated in NO detection, bacterial replication in phagocytes, intracellular phenotypic heterogeneity, and biofilm formation.

An active learning card game to teach microbial pathogenesis to undergraduate biology majors

Interactive classroom activities are an effective way to reinforce knowledge and promote student engagement. In this paper, we introduce the Pathogenesis Card Game (PCG), an innovative card game that engages students in a battle between microbial pathogens and the host immune system. Each student is given a set of cards that consist of either common host defenses or common pathogen evasion strategies. In pairs, students play a host defense card versus a pathogenesis card. Host defense cards include neutralize (antibody production), eat (phagocytosis), and destroy (degranulation). Pathogenesis cards present evasive strategies including mimic (molecular mimicry), escape (hemolysin production), hide (polysaccharide capsule), block (antioxidant defense), cut (protease secretion), and disguise (antigenic variation). Students develop a mastery of microbial pathogenesis through active gameplay by deliberating the outcome of each unique host-pathogen interaction. Furthermore, they learn the role of cells in the immune system and how pathogens can evade these immune defenses. PCG was piloted in a 300-level introductory microbiology course for 22 undergraduate students, comprising primarily biology and nursing majors. Both quantitative and qualitative student evaluations of the activity strongly suggest that PCG is an engaging, effective, and useful way to teach microbial pathogenesis. This activity provides a 60-minute lesson plan and corresponding materials that can be used to facilitate the introduction of pathogenesis to a typical undergraduate microbiology course. PCG offers instructors a framework to teach microbial pathogenesis and gives students the opportunity to construct their own knowledge about pathogen immune evasion in an engaging and interactive way.

Proximity labeling of host factor ANXA3 in HCV infection reveals a novel LARP1 function in viral entry

Hepatitis C virus (HCV) infection is tightly connected to the lipid metabolism with lipid droplets (LDs) serving as assembly sites for progeny virions. A previous LD proteome analysis identified annexin A3 (ANXA3) as an important HCV host factor that is enriched at LDs in infected cells and required for HCV morphogenesis. To further characterize ANXA3 function in HCV, we performed proximity labeling using ANXA3-BioID2 as bait in HCV-infected cells. Two of the top proteins identified proximal to ANXA3 during HCV infection were the La-related protein 1 (LARP1) and the ADP ribosylation factor-like protein 8B (ARL8B), both of which have been previously described to act in HCV particle production. In follow-up experiments, ARL8B functioned as a pro-viral HCV host factor without localizing to LDs and thus likely independent of ANXA3. In contrast, LARP1 interacts with HCV core protein in an RNA-dependent manner and is translocated to LDs by core protein. Knockdown of LARP1 decreased HCV spreading without altering HCV RNA replication or viral titers. Unexpectedly, entry of HCV particles and E1/E2-pseudotyped lentiviral particles was reduced by LARP1 depletion, whereas particle production was not altered. Using a recombinant vesicular stomatitis virus (VSV)ΔG entry assay, we showed that LARP1 depletion also decreased entry of VSV with VSV, MERS, and CHIKV glycoproteins. Therefore, our data expand the role of LARP1 as an HCV host factor that is most prominently involved in the early steps of infection, likely contributing to endocytosis of viral particles through the pleiotropic effect LARP1 has on the cellular translatome.

Deciphering protein prenylation in endocytic trafficking in Toxoplasma gondii

Toxoplasma gondii is a widespread intracellular protozoan pathogen infecting virtually all warm-blooded animals. This parasite acquires host-derived resources to support its replication inside a membrane-bound parasitophorous vacuole within infected host cells. Previous research has discovered that Toxoplasma actively endocytoses host proteins and transports them to a lysosome-equivalent structure for digestion. However, few molecular determinants required for trafficking of host-derived material within the parasite were known. A recent study (Q.-Q. Wang, M. Sun, T. Tang, D.-H. Lai, et al., mBio 14:e01309-23, 2023, https://doi.org/10.1128/mbio.01309-23) identified a critical role for membrane anchoring of proteins via prenylation in the trafficking of endocytosed host proteins by Toxoplasma, including an essential Toxoplasma ortholog of Rab1B. The authors also found that TgRab1 is crucial for protein trafficking of the rhoptry secretory organelles, indicating a dual role in endocytic and exocytic protein trafficking. This study sets the stage for further dissecting endomembrane trafficking in Toxoplasma, along with potentially exploiting protein prenylation as a target for therapeutic development.

Ceramide-1-phosphate is a regulator of Golgi structure and is co-opted by the obligate intracellular bacterial pathogen Anaplasma phagocytophilum

Many intracellular pathogens structurally disrupt the Golgi apparatus as an evolutionarily conserved promicrobial strategy. Yet, the host factors and signaling processes involved are often poorly understood, particularly for Anaplasma phagocytophilum, the agent of human granulocytic anaplasmosis. We found that A. phagocytophilum elevated cellular levels of the bioactive sphingolipid, ceramide-1-phosphate (C1P), to promote Golgi fragmentation that enables bacterial proliferation, conversion from its non-infectious to infectious form, and productive infection. A. phagocytophilum poorly infected mice deficient in ceramide kinase, the Golgi-localized enzyme responsible for C1P biosynthesis. C1P regulated Golgi morphology via activation of a PKCα/Cdc42/JNK signaling axis that culminates in phosphorylation of Golgi structural proteins, GRASP55 and GRASP65. siRNA-mediated depletion of Cdc42 blocked A. phagocytophilum from altering Golgi morphology, which impaired anterograde trafficking of trans-Golgi vesicles into and maturation of the pathogen-occupied vacuole. Cells overexpressing phosphorylation-resistant versions of GRASP55 and GRASP65 presented with suppressed C1P- and A. phagocytophilum-induced Golgi fragmentation and poorly supported infection by the bacterium. By studying A. phagocytophilum, we identify C1P as a regulator of Golgi structure and a host factor that is relevant to disease progression associated with Golgi fragmentation.IMPORTANCECeramide-1-phosphate (C1P), a bioactive sphingolipid that regulates diverse processes vital to mammalian physiology, is linked to disease states such as cancer, inflammation, and wound healing. By studying the obligate intracellular bacterium Anaplasma phagocytophilum, we discovered that C1P is a major regulator of Golgi morphology. A. phagocytophilum elevated C1P levels to induce signaling events that promote Golgi fragmentation and increase vesicular traffic into the pathogen-occupied vacuole that the bacterium parasitizes. As several intracellular microbial pathogens destabilize the Golgi to drive their infection cycles and changes in Golgi morphology is also linked to cancer and neurodegenerative disorder progression, this study identifies C1P as a potential broad-spectrum therapeutic target for infectious and non-infectious diseases.

A genome-wide CRISPR screen identified host genes essential for intracellular Brucella survival

Brucella is a zoonotic intracellular bacterium that poses threats to human health and economic security. Intracellular infection is a hallmark of the agent Brucella and a primary cause of distress, through which the bacterium regulates the host intracellular environment to promote its own colonization and replication, evading host immunity and pharmaceutical killing. Current studies of Brucella intracellular processes are typically premised on bacterial phenotype such as intracellular bacterial survival, followed by biochemical or molecular biological approaches to reveal detailed mechanisms. While such processes can deepen the understanding of Brucella-host interaction, the insights into host alterations in infection would be easily restricted to known pathways. In the current study, we applied CRISPR Cas9 screen to identify host genes that are most affected by Brucella infection on cell viability at the genomic level. As a result of CRISPR screening, we firstly identified that knockout of the negatively selected genes GOLGA6L6, DEFB103B, OR4F29, and ERCC6 attenuate the viability of both the host cells and intracellular Brucella, suggesting these genes to be potential therapeutic targets for Brucella control. In particular, knockout of DEFB103B diminished Brucella intracellular survival by altering host cell autophagy. Conversely, knockout of positive screening genes promoted intracellular proliferation of Brucella. In summary, we screened host genes at the genomic level throughout Brucella infection, identified host genes that are previously not recognized to be involved in Brucella infection, and provided targets for intracellular infection control.IMPORTANCEBrucella is a Gram-negative bacterium that infects common mammals causing arthritis, myalgia, neuritis, orchitis, or miscarriage and is difficult to cure with antibiotics due to its intracellular parasitism. Therefore, unraveling the mechanism of Brucella-host interactions will help controlling Brucella infections. CRISPR-Cas9 is a gene editing technology that directs knockout of individual target genes by guided RNA, from which genome-wide gene-knockout cell libraries can be constructed. Upon infection with Brucella, the cell library would show differences in viability as a result of the knockout and specific genes could be revealed by genomic DNA sequencing. As a result, genes affecting cell viability during Brucella infection were identified. Further testing of gene function may reveal the mechanisms of Brucella-host interactions, thereby contributing to clinical therapy.

Interaction between host G3BP and viral nucleocapsid protein regulates SARS-CoV-2 replication and pathogenicity

G3BP1/2 are paralogous proteins that promote stress granule formation in response to cellular stresses, including viral infection. The nucleocapsid (N) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) inhibits stress granule assembly and interacts with G3BP1/2 via an ITFG motif, including residue F17, in the N protein. Prior studies examining the impact of the G3PB1-N interaction on SARS-CoV-2 replication have produced inconsistent findings, and the role of this interaction in pathogenesis is unknown. Here, we use structural and biochemical analyses to define the residues required for G3BP1-N interaction and structure-guided mutagenesis to selectively disrupt this interaction. We find that N-F17A mutation causes highly specific loss of interaction with G3BP1/2. SARS-CoV-2 N-F17A fails to inhibit stress granule assembly in cells, has decreased viral replication, and causes decreased pathology in vivo. Further mechanistic studies indicate that the N-F17-mediated G3BP1-N interaction promotes infection by limiting sequestration of viral genomic RNA (gRNA) into stress granules.

Uncovering the diversity of pathogenic invaders: insights into protozoa, fungi, and worm infections

Post COVID-19, there has been renewed interest in understanding the pathogens challenging the human health and evaluate our preparedness towards dealing with health challenges in future. In this endeavour, it is not only the bacteria and the viruses, but a greater community of pathogens. Such pathogenic microorganisms, include protozoa, fungi and worms, which establish a distinct variety of disease-causing agents with the capability to impact the host's well-being as well as the equity of ecosystem. This review summarises the peculiar characteristics and pathogenic mechanisms utilized by these disease-causing organisms. It features their role in causing infection in the concerned host and emphasizes the need for further research. Understanding the layers of pathogenesis encompassing the concerned infectious microbes will help expand targeted inferences with relation to the cause of the infection. This would strengthen and augment benefit to the host's health along with the maintenance of ecosystem network, exhibiting host-pathogen interaction cycle. This would be key to discover the layers underlying differential disease severities in response to similar/same pathogen infection.

Protective potential of outer membrane vesicles derived from a virulent strain of Francisella tularensis

Francisella tularensis secretes tubular outer membrane vesicles (OMVs) that contain a number of immunoreactive proteins as well as virulence factors. We have reported previously that isolated Francisella OMVs enter macrophages, cumulate inside, and induce a strong pro-inflammatory response. In the current article, we present that OMVs treatment of macrophages also enhances phagocytosis of the bacteria and suppresses their intracellular replication. On the other hand, the subsequent infection with Francisella is able to revert to some extent the strong pro-inflammatory effect induced by OMVs in macrophages. Being derived from the bacterial surface, isolated OMVs may be considered a "non-viable mixture of Francisella antigens" and as such, they present a promising protective material. Immunization of mice with OMVs isolated from a virulent F. tularensis subsp. holarctica strain FSC200 prolonged the survival time but did not fully protect against the infection with a lethal dose of the parent strain. However, the sera of the immunized animals revealed unambiguous cytokine and antibody responses and proved to recognize a set of well-known Francisella immunoreactive proteins. For these reasons, Francisella OMVs present an interesting material for future protective studies.

Corrigendum: Inflammatory response against Staphylococcus aureus via intracellular sensing of nucleic acids in keratinocytes

[This corrects the article DOI: 10.3389/fimmu.2022.828626.].

Scs system links copper and redox homeostasis in bacterial pathogens

The bacterial envelope is an essential compartment involved in metabolism and metabolites transport, virulence, and stress defense. Its roles become more evident when homeostasis is challenged during host-pathogen interactions. In particular, the presence of free radical groups and excess copper in the periplasm causes noxious reactions, such as sulfhydryl group oxidation leading to enzymatic inactivation and protein denaturation. In response to this, canonical and accessory oxidoreductase systems are induced, performing quality control of thiol groups, and therefore contributing to restoring homeostasis and preserving survival under these conditions. Here, we examine recent advances in the characterization of the Dsb-like, Salmonella-specific Scs system. This system includes the ScsC/ScsB pair of Cu+-binding proteins with thiol-oxidoreductase activity, an alternative ScsB-partner, the membrane-linked ScsD, and a likely associated protein, ScsA, with a role in peroxide resistance. We discuss the acquisition of the scsABCD locus and its integration into a global regulatory pathway directing envelope response to Cu stress during the evolution of pathogens that also harbor the canonical Dsb systems. The evidence suggests that the canonical Dsb systems cannot satisfy the extra demands that the host-pathogen interface imposes to preserve functional thiol groups. This resulted in the acquisition of the Scs system by Salmonella. We propose that the ScsABCD complex evolved to connect Cu and redox stress responses in this pathogen as well as in other bacterial pathogens.

The bacterial pathogen Pseudomonas plecoglossicida, its epidemiology, virulence factors, vaccine development, and host-pathogen interactions

OBJECTIVE

Pseudomoans plecoglossicida has been identified as a fish pathogen since 2000 and has caused serious infections in cultured Large Yellow Croakers Larimiththys crocea in coastal eastern China during recent years.

METHODS

Published literatures of this pathogen have been reviewed.

RESULT

Several strains with high genomic similarity have been isolated and identified; the bacteria induce natural infection at lower water temperatures (12.0-25.5°C) and induce numerous granulomas and nodules in the visceral organs of croakers. Researchers have investigated the epidemiology of P. plecoglossicida infection, identified major virulence factors, searched for pathogenic genes, analyzed host-pathogen interactions, and endeavored to develop efficient vaccines.

CONCLUSION

This paper provides an overview of these research advances to elucidate the virulence mechanisms of the pathogen and to promote vaccine development against infection.

Oral infectivity through carnivorism in murine model of Trypanosoma cruzi infection

Introduction

Oral transmission of T. cruzi is probably the most frequent transmission mechanism in wild animals. This observation led to the hypothesis that consuming raw or undercooked meat from animals infected with T. cruzi may be responsible for transmitting the infection. Therefore, the general objective of this study was to investigate host-pathogen interactions between the parasite and gastric mucosa and the role of meat consumption from infected animals in the oral transmission of T. cruzi.

Methods

Cell infectivity assays were performed on AGS cells in the presence or absence of mucin, and the roles of pepsin and acidic pH were determined. Moreover, groups of five female Balb/c mice were fed with muscle tissue obtained from mice in the acute phase of infection by the clone H510 C8C3hvir of T. cruzi, and the infection of the fed mice was monitored by a parasitemia curve. Similarly, we assessed the infective capacity of T. cruzi trypomastigotes and amastigotes by infecting groups of five mice Balb/c females, which were infected orally using a nasogastric probe, and the infection was monitored by a parasitemia curve. Finally, different trypomastigote and amastigote inoculums were used to determine their infective capacities. Adhesion assays of T. cruzi proteins to AGS stomach cells were performed, and the adhered proteins were detected by western blotting using monoclonal or polyclonal antibodies and by LC-MS/MS and bioinformatics analysis.

Results

Trypomastigote migration in the presence of mucin was reduced by approximately 30%, whereas in the presence of mucin and pepsin at pH 3.5, only a small proportion of parasites were able to migrate (∼6%). Similarly, the ability of TCTs to infect AGS cells in the presence of mucin is reduced by approximately 20%. In all cases, 60-100% of the animals were fed meat from mice infected in the acute phase or infected with trypomastigotes or amastigotes developed high parasitemia, and 80% died around day 40 post-infection. The adhesion assay showed that cruzipain is a molecule of trypomastigotes and amastigotes that binds to AGS cells. LC-MS/MS and bioinformatics analysis, also confirmed that transialidase, cysteine proteinases, and gp63 may be involved in TCTs attachment or invasion of human stomach cells because they can potentially interact with different proteins in the human stomach mucosa. In addition, several human gastric mucins have cysteine protease cleavage sites.

Discussion

Then, under our experimental conditions, consuming meat from infected animals in the acute phase allows the T. cruzi infection. Similarly, trypomastigotes and amastigotes could infect mice when administered orally, whereas cysteinyl proteinases and trans-sialidase appear to be relevant molecules in this infective process.

Unraveling the transcriptional features and gene expression networks of pathogenic and saprotrophic Ophiostoma species during the infection of Ulmus americana

American elm (Ulmus americana), highly prized for its ornamental value, has suffered two successive outbreaks of Dutch elm disease (DED) caused by ascomycete fungi belonging to the genus Ophiostoma. To identify the genes linked to the pathogenicity of different species and lineages of Ophiostoma, we inoculated 2-year-old U. americana saplings with six strains representing three species of DED fungi, and one strain of the saprotroph Ophiostoma quercus. Differential expression analyses were performed following RNA sequencing of fungal transcripts recovered at 3- and 10-days post-infection. Based on a total of 8,640 Ophiostoma genes, we observed a difference in fungal gene expression depending on the strain inoculated and the time of incubation in host tissue. Some genes overexpressed in the more virulent strains of Ophiostoma encode hydrolases that possibly act synergistically. A mutant of Ophiostoma novo-ulmi in which the gene encoding the ogf1 transcription factor had been deleted did not produce transcripts for the gene encoding the hydrophobin cerato-ulmin and was less virulent. Weighted gene correlation network analyses identified several candidate pathogenicity genes distributed among 13 modules of interconnected genes.IMPORTANCEOphiostoma is a genus of cosmopolitan fungi that belongs to the family Ophiostomataceae and includes the pathogens responsible for two devastating pandemics of Dutch elm disease (DED). As the mechanisms of action of DED agents remain unclear, we carried out the first comparative transcriptomic study including representative strains of the three Ophiostoma species causing DED, along with the phylogenetically close saprotrophic species Ophiostoma quercus. Statistical analyses of the fungal transcriptomes recovered at 3 and 10 days following infection of Ulmus americana saplings highlighted several candidate genes associated with virulence and host-pathogen interactions wherein each strain showed a distinct transcriptome. The results of this research underscore the importance of investigating the transcriptional behavior of different fungal taxa to understand their pathogenicity and virulence in relation to the timeline of infection.

Varying conjunctival immune response adaptations of house finch populations to a rapidly evolving bacterial pathogen

Pathogen adaptations during host-pathogen co-evolution can cause the host balance between immunity and immunopathology to rapidly shift. However, little is known in natural disease systems about the immunological pathways optimised through the trade-off between immunity and self-damage. The evolutionary interaction between the conjunctival bacterial infection Mycoplasma gallisepticum (MG) and its avian host, the house finch (Haemorhous mexicanus), can provide insights into such adaptations in immune regulation. Here we use experimental infections to reveal immune variation in conjunctival tissue for house finches captured from four distinct populations differing in the length of their co-evolutionary histories with MG and their disease tolerance (defined as disease severity per pathogen load) in controlled infection studies. To differentiate contributions of host versus pathogen evolution, we compared house finch responses to one of two MG isolates: the original VA1994 isolate and a more evolutionarily derived one, VA2013. To identify differential gene expression involved in initiation of the immune response to MG, we performed 3'-end transcriptomic sequencing (QuantSeq) of samples from the infection site, conjunctiva, collected 3-days post-infection. In response to MG, we observed an increase in general pro-inflammatory signalling, as well as T-cell activation and IL17 pathway differentiation, associated with a decrease in the IL12/IL23 pathway signalling. The immune response was stronger in response to the evolutionarily derived MG isolate compared to the original one, consistent with known increases in MG virulence over time. The host populations differed namely in pre-activation immune gene expression, suggesting population-specific adaptations. Compared to other populations, finches from Virginia, which have the longest co-evolutionary history with MG, showed significantly higher expression of anti-inflammatory genes and Th1 mediators. This may explain the evolution of disease tolerance to MG infection in VA birds. We also show a potential modulating role of BCL10, a positive B- and T-cell regulator activating the NFKB signalling. Our results illuminate potential mechanisms of house finch adaptation to MG-induced immunopathology, contributing to understanding of the host evolutionary responses to pathogen-driven shifts in immunity-immunopathology trade-offs.

The Pseudomonas aeruginosa lectin LecB modulates intracellular reactive oxygen species production in human neutrophils

Pseudomonas aeruginosa is a Gram-negative bacterium and an opportunistic pathogen ubiquitously present throughout nature. LecB, a fucose-, and mannose-binding lectin, is a prominent virulence factor of P. aeruginosa, which can be expressed on the bacterial surface but also be secreted. However, the LecB interaction with human immune cells remains to be characterized. Neutrophils comprise the first line of defense against infections and their production of reactive oxygen species (ROS) and release of extracellular traps (NETs) are critical antimicrobial mechanisms. When profiling the neutrophil glycome we found several glycoconjugates on granule and plasma membranes that could potentially act as LecB receptors. In line with this, we here show that soluble LecB can activate primed neutrophils to produce high levels of intracellular ROS (icROS), an effect that was inhibited by methyl fucoside. On the other hand, soluble LecB inhibits P. aeruginosa-induced icROS production. In support of that, during phagocytosis of wild-type and LecB-deficient P. aeruginosa, bacteria with LecB induced less icROS production as compared with bacteria lacking the lectin. Hence, LecB can either induce or inhibit icROS production in neutrophils depending on the circumstances, demonstrating a novel and potential role for LecB as an immunomodulator of neutrophil functional responses.

Prophylactic Oral Application of Activated Charcoal Mitigates Acute Campylobacteriosis in Human Gut Microbiota-Associated IL-10-/- Mice

The incidence of human Campylobacter jejuni infections is increasing worldwide. It is highly desirable to prevent campylobacteriosis in individuals at risk for severe disease with antibiotics-independent non-toxic compounds. Activated charcoal (AC) has long been used as an anti-diarrheal remedy. Here, we tested the disease-mitigating effects of oral AC versus placebo in human gut microbiota-associated (hma) IL-10-/- mice starting a week prior to C. jejuni infection. On day 6 post-infection, the gastrointestinal C. jejuni loads were comparable in both infected cohorts, whereas campylobacteriosis symptoms such as wasting and bloody diarrhea were mitigated upon AC prophylaxis. Furthermore, AC application resulted in less pronounced C. jejuni-induced colonic epithelial cell apoptosis and in dampened innate and adaptive immune cell responses in the colon that were accompanied by basal concentrations of pro-inflammatory mediators including IL-6, TNF-α, IFN-γ, and nitric oxide measured in colonic explants from AC treated mice on day 6 post-infection. Furthermore, C. jejuni infection resulted in distinct fecal microbiota shift towards higher enterobacterial numbers and lower loads of obligate anaerobic species in hma mice that were AC-independent. In conclusion, our pre-clinical placebo-controlled intervention study provides evidence that prophylactic oral AC application mitigates acute murine campylobacteriosis.

Recent advances in infectious disease research using cryo-electron tomography

With the increasing spread of infectious diseases worldwide, there is an urgent need for novel strategies to combat them. Cryogenic sample electron microscopy (cryo-EM) techniques, particularly electron tomography (cryo-ET), have revolutionized the field of infectious disease research by enabling multiscale observation of biological structures in a near-native state. This review highlights the recent advances in infectious disease research using cryo-ET and discusses the potential of this structural biology technique to help discover mechanisms of infection in native environments and guiding in the right direction for future drug discovery.

Klebsiella pneumoniae OmpR facilitates lung infection through transcriptional regulation of key virulence factors

IMPORTANCE

Bacteria use two-component regulatory systems (TCSs) to adapt to changes in their environment by changing their gene expression. In this study, we show that the EnvZ/OmpR TCS of the clinically relevant opportunistic pathogen Klebsiella pneumoniae plays an important role in successfully establishing lung infection and virulence. In addition, we elucidate the K. pneumoniae OmpR regulon within the host. This work suggests that K. pneumoniae OmpR might be a promising target for innovative anti-infectives.

Toxoplasma gondii mitochondrial association factor 1b interactome reveals novel binding partners including Ral GTPase accelerating protein α1

The intracellular parasite, Toxoplasma gondii, has developed sophisticated molecular strategies to subvert host processes and promote growth and survival. During infection, T. gondii replicates in a parasitophorous vacuole (PV) and modulates host functions through a network of secreted proteins. Of these, Mitochondrial Association Factor 1b (MAF1b) recruits host mitochondria to the PV, a process that confers an in vivo growth advantage, though the precise mechanisms remain enigmatic. To address this knowledge gap, we mapped the MAF1b interactome in human fibroblasts using a commercial Yeast-2-hybrid (Y2H) screen, which revealed several previously unidentified binding partners including the GAP domain of Ral GTPase Accelerating Protein α1 (RalGAPα1(GAP)). Recombinantly produced MAF1b and RalGAPα1(GAP) formed as a stable binary complex as shown by size exclusion chromatography with a Kd of 334 nM as measured by isothermal titration calorimetry (ITC). Notably, no binding was detected between RalGAPα1(GAP) and the structurally conserved MAF1b homolog, MAF1a, which does not recruit host mitochondria. Next, we used hydrogen deuterium exchange mass spectrometry (HDX-MS) to map the RalGAPα1(GAP)-MAF1b interface, which led to identification of the "GAP-binding loop" on MAF1b that was confirmed by mutagenesis and ITC to be necessary for complex formation. A high-confidence Alphafold model predicts the GAP-binding loop to lie at the RalGAPα1(GAP)-MAF1b interface further supporting the HDX-MS data. Mechanistic implications of a RalGAPα1(GAP)-MAF1b complex are discussed in the context of T. gondii infection and indicates that MAF1b may have evolved multiple independent functions to increase T. gondii fitness.

The same boat, different storm: stress volatile emissions in response to biotrophic fungal infections in primary and alternate hosts

Rust infection results in stress volatile emissions, but due to the complexity of host-pathogen interaction and variations in innate defense and capacity to induce defense, biochemical responses can vary among host species. Fungal-dependent modifications in volatile emissions have been well documented in numerous host species, but how emission responses vary among host species is poorly understood. Our recent experiments demonstrated that the obligate biotrophic crown rust fungus (P. coronata) differently activated primary and secondary metabolic pathways in its primary host Avena sativa and alternate host Rhamnus frangula. In A. sativa, emissions of methyl jasmonate, short-chained lipoxygenase products, long-chained saturated fatty acid derivatives, mono- and sesquiterpenes, carotenoid breakdown products, and benzenoids were initially elicited in an infection severity-dependent manner, but the emissions decreased under severe infection and photosynthesis was almost completely inhibited. In R. frangula, infection resulted in low-level induction of stress volatile emissions, but surprisingly, in enhanced constitutive isoprene emissions, and even severely-infected leaves maintained a certain photosynthesis rate. Thus, the same pathogen elicited a much stronger response in the primary than in the alternate host. We argue that future work should focus on resolving mechanisms of different fungal tolerance and resilience among primary and secondary hosts.

Chlamydial YAP activation in host endocervical epithelial cells mediates pro-fibrotic paracrine stimulation of fibroblasts

IMPORTANCE

Chronic or repeated infection of the female upper genital tract by C. trachomatis can lead to severe fibrotic sequelae, including tubal factor infertility and ectopic pregnancy. However, the molecular mechanisms underlying this effect are unclear. In this report, we define a transcriptional program specific to C. trachomatis infection of the upper genital tract, identifying tissue-specific induction of host YAP-a pro-fibrotic transcriptional cofactor-as a potential driver of infection-mediated fibrotic gene expression. Furthermore, we show that infected endocervical epithelial cells stimulate collagen production by fibroblasts and implicate chlamydial induction of YAP in this effect. Our results define a mechanism by which infection mediates tissue-level fibrotic pathology via paracrine signaling and identify YAP as a potential therapeutic target for the prevention of Chlamydia-associated scarring of the female genital tract.

Prophylactic oral application of resveratrol to alleviate acute campylobacteriosis in human gut microbiota associated IL-10-/- mice

Human infections with the food-borne zoonotic enteropathogen Campylobacter jejuni are increasing globally. Since multi-drug resistant bacterial strains are further on the rise, antibiotic-independent measures are needed to fight campylobacteriosis. Given its anti-microbial and anti-inflammatory properties the polyphenolic compound resveratrol constitutes such a promising candidate molecule. In our present placebo-controlled intervention trial, synthetic resveratrol was applied perorally to human gut microbiota-associated (hma) IL-10-/- mice starting a week before oral C. jejuni infection. Our analyses revealed that the resveratrol prophylaxis did not interfere with the establishment of C. jejuni within the murine gastrointestinal tract on day 6 post-infection, but alleviated clinical signs of campylobacteriosis and resulted in less distinct colonic epithelial apoptosis. Furthermore, oral resveratrol dampened C. jejuni-induced colonic T and B cell responses as well as intestinal secretion of pro-inflammatory mediators including nitric oxide, IL-6, TNF-α, and IFN-γ to basal levels. Moreover, resveratrol application was not accompanied by significant shifts in the colonic commensal microbiota composition during campylobacteriosis in hma IL-10-/- mice. In conclusion, our placebo-controlled intervention study provides evidence that prophylactic oral application of resveratrol constitutes a promising strategy to alleviate acute campylobacteriosis and in consequence, to reduce the risk for post-infectious autoimmune sequelae.

KLF17 is an important regulatory component of the transcriptomic response of Atlantic salmon macrophages to Piscirickettsia salmonis infection

Piscirickettsia salmonis is the most important health problem facing Chilean Aquaculture. Previous reports suggest that P. salmonis can survive in salmonid macrophages by interfering with the host immune response. However, the relevant aspects of the molecular pathogenesis of P. salmonis have been poorly characterized. In this work, we evaluated the transcriptomic changes in macrophage-like cell line SHK-1 infected with P. salmonis at 24- and 48-hours post-infection (hpi) and generated network models of the macrophage response to the infection using co-expression analysis and regulatory transcription factor-target gene information. Transcriptomic analysis showed that 635 genes were differentially expressed after 24- and/or 48-hpi. The pattern of expression of these genes was analyzed by weighted co-expression network analysis (WGCNA), which classified genes into 4 modules of expression, comprising early responses to the bacterium. Induced genes included genes involved in metabolism and cell differentiation, intracellular transportation, and cytoskeleton reorganization, while repressed genes included genes involved in extracellular matrix organization and RNA metabolism. To understand how these expression changes are orchestrated and to pinpoint relevant transcription factors (TFs) controlling the response, we established a curated database of TF-target gene regulatory interactions in Salmo salar, SalSaDB. Using this resource, together with co-expression module data, we generated infection context-specific networks that were analyzed to determine highly connected TF nodes. We found that the most connected TF of the 24- and 48-hpi response networks is KLF17, an ortholog of the KLF4 TF involved in the polarization of macrophages to an M2-phenotype in mammals. Interestingly, while KLF17 is induced by P. salmonis infection, other TFs, such as NOTCH3 and NFATC1, whose orthologs in mammals are related to M1-like macrophages, are repressed. In sum, our results suggest the induction of early regulatory events associated with an M2-like phenotype of macrophages that drives effectors related to the lysosome, RNA metabolism, cytoskeleton organization, and extracellular matrix remodeling. Moreover, the M1-like response seems delayed in generating an effective response, suggesting a polarization towards M2-like macrophages that allows the survival of P. salmonis. This work also contributes to SalSaDB, a curated database of TF-target gene interactions that is freely available for the Atlantic salmon community.

Common scab disease: structural basis of elicitor recognition in pathogenic Streptomyces species

IMPORTANCE

Common scab is a disease caused by a few Streptomyces species that affects important root and tuber crops including potato, beet, radish, and parsnip, resulting in major economic losses worldwide. In this work, we unveiled the molecular basis of host recognition by these pathogens by solving the structure of the sugar-binding protein CebE of Streptomyces scabiei in complex with cellotriose, the main elicitor of the pathogenic lifestyle of these bacteria. We further revealed that the signaling pathway from CebE-mediated transport of cellotriose is conserved in all pathogenic species except Streptomyces ipomoeae, which causes soft rot disease in sweet potatoes. Our work also provides the structural basis of the uptake of cellobiose and cellotriose in saprophytic Streptomyces species, the first step activating the expression of the enzymatic system degrading the most abundant polysaccharide on earth, cellulose.

Fasciolosis: pathogenesis, host-parasite interactions, and implication in vaccine development

Fasciola hepatica is distributed worldwide, causing substantial economic losses in the animal husbandry industry. Human fasciolosis is an emerging zoonosis in Andean America, Asia, and Africa. The control of the disease, both in humans and animals, is based on using anthelmintic drugs, which has resulted in increased resistance to the most effective anthelmintics, such as triclabendazole, in many countries. This, together with the concerns about drug residues in food and the environment, has increased the interest in preventive measures such as a vaccine to help control the disease in endemic areas. Despite important efforts over the past two decades and the work carried out with numerous vaccine candidates, none of them has demonstrated consistent and reproducible protection in target species. This is at least in part due to the high immunomodulation capacity of the parasite, making ineffective the host response in susceptible species such as ruminants. It is widely accepted that a deeper knowledge of the host-parasite interactions is needed for a more rational design of vaccine candidates. In recent years, the use of emerging technologies has notably increased the amount of data about these interactions. In the present study, current knowledge of host-parasite interactions and their implication in Fasciola hepatica vaccine development is reviewed.

The Legionella autoinducer LAI-1 is delivered by outer membrane vesicles to promote interbacterial and interkingdom signaling

Legionella pneumophila is an environmental bacterium, which replicates in amoeba but also in macrophages, and causes a life-threatening pneumonia called Legionnaires' disease. The opportunistic pathogen employs the α-hydroxy-ketone compound Legionella autoinducer-1 (LAI-1) for intraspecies and interkingdom signaling. LAI-1 is produced by the autoinducer synthase Legionella quorum sensing A (LqsA), but it is not known, how LAI-1 is released by the pathogen. Here, we use a Vibrio cholerae luminescence reporter strain and liquid chromatography-tandem mass spectrometry to detect bacteria-produced and synthetic LAI-1. Ectopic production of LqsA in Escherichia coli generated LAI-1, which partitions to outer membrane vesicles (OMVs) and increases OMV size. These E. coli OMVs trigger luminescence of the V. cholerae reporter strain and inhibit the migration of Dictyostelium discoideum amoeba. Overexpression of lqsA in L.pneumophila under the control of strong stationary phase promoters (PflaA or P6SRNA), but not under control of its endogenous promoter (PlqsA), produces LAI-1, which is detected in purified OMVs. These L. pneumophila OMVs trigger luminescence of the Vibrio reporter strain and inhibit D. discoideum migration. L. pneumophila OMVs are smaller upon overexpression of lqsA or upon addition of LAI-1 to growing bacteria, and therefore, LqsA affects OMV production. The overexpression of lqsA but not a catalytically inactive mutant promotes intracellular replication of L. pneumophila in macrophages, indicating that intracellularly produced LA1-1 modulates the interaction in favor of the pathogen. Taken together, we provide evidence that L. pneumophila LAI-1 is secreted through OMVs and promotes interbacterial communication and interactions with eukaryotic host cells.

Comparative spatial proteomics of Plasmodium-infected erythrocytes

Plasmodium parasites contribute to one of the highest global infectious disease burdens. To achieve this success, the parasite has evolved a range of specialized subcellular compartments to extensively remodel the host cell for its survival. The information to fully understand these compartments is likely hidden in the so far poorly characterized Plasmodium species spatial proteome. To address this question, we determined the steady-state subcellular location of more than 12,000 parasite proteins across five different species by extensive subcellular fractionation of erythrocytes infected by Plasmodium falciparum, Plasmodium knowlesi, Plasmodium yoelii, Plasmodium berghei, and Plasmodium chabaudi. This comparison of the pan-species spatial proteomes and their expression patterns indicates increasing species-specific proteins associated with the more external compartments, supporting host adaptations and post-transcriptional regulation. The spatial proteome offers comprehensive insight into the different human, simian, and rodent Plasmodium species, establishing a powerful resource for understanding species-specific host adaptation processes in the parasite.

Oral application of carvacrol, butyrate, ellagic acid, and 2'-fucosyl-lactose to mice suffering from acute campylobacteriosis - Results from a preclinical placebo-controlled intervention study

Background

Acute campylobacteriosis caused by oral infections with the enteropathogen Campylobacter jejuni represent serious threats to global human health. Since novel treatment options with safe and antibiotics-independent compounds would be highly appreciable, we here investigated the anti-bacterial and disease-alleviating effects of carvacrol, butyrate, ellagic acid, and 2'-fucosyl-lactose in acute murine campylobacteriosis. To address this, secondary abiotic IL-10-/- mice were perorally infected with C. jejuni and treated with either compound alone or all four in combination via the drinking water starting two days post-infection.

Results

On day 6, the duodenal pathogen loads were lower in mice of the combination versus the vehicle treatment cohort. Importantly, mice treated with carvacrol and the combination presented with less distinct diarrheal symptoms, colonic histopathology, epithelial cell apoptosis, and immune cell responses when compared to vehicle counterparts on day 6 post-infection. Furthermore, the combination treatment did not only diminish colonic IFN-γ, TNF-α, and IL-6 secretion in C. jejuni infected mice, but also dampened extra-intestinal and even systemic pro-inflammatory cytokine concentrations to basal levels as measured in liver, kidneys, lungs, and serum samples.

Conclusions

Our preclinical placebo-controlled intervention trial provides evidence that the combined oral application of carvacrol, butyrate, ellagic acid, and 2'-fucosyl-lactose alleviates acute campylobacteriosis in the vertebrate host.

Transcriptional Profiling of SARS-CoV-2-Infected Calu-3 Cells Reveals Immune-Related Signaling Pathways

The COVID-19 disease, caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), emerged in late 2019 and rapidly spread worldwide, becoming a pandemic that infected millions of people and caused significant deaths. COVID-19 continues to be a major threat, and there is a need to deepen our understanding of the virus and its mechanisms of infection. To study the cellular responses to SARS-CoV-2 infection, we performed an RNA sequencing of infected vs. uninfected Calu-3 cells. Total RNA was extracted from infected (0.5 MOI) and control Calu-3 cells and converted to cDNA. Sequencing was performed, and the obtained reads were quality-analyzed and pre-processed. Differential expression was assessed with the EdgeR package, and functional enrichment was performed in EnrichR for Gene Ontology, KEGG pathways, and WikiPathways. A total of 1040 differentially expressed genes were found in infected vs. uninfected Calu-3 cells, of which 695 were up-regulated and 345 were down-regulated. Functional enrichment analyses revealed the predominant up-regulation of genes related to innate immune response, response to virus, inflammation, cell proliferation, and apoptosis. These transcriptional changes following SARS-CoV-2 infection may reflect a cellular response to the infection and help to elucidate COVID-19 pathogenesis, in addition to revealing potential biomarkers and drug targets.

Immersion challenge of three salmonid species (family Salmonidae) with three multilocus sequence typing variants of Flavobacterium psychrophilum provides evidence of differential host specificity

Bacterial coldwater disease (BCWD), caused by Flavobacterium psychrophilum, results in significant losses among multiple salmonid (family Salmonidae) species. Molecular epidemiology and serotyping studies have suggested that some variants are host specific; however, these associations have not been evaluated by cross-challenging fish species with putatively host-associated F. psychrophilum isolates via more natural (i.e. immersion) exposure routes. To this end, F. psychrophilum isolates US19-COS, US62-ATS and US87-RBT, each originally recovered from diseased coho salmon (Oncorhynchus kisutch), Atlantic salmon (Salmo salar) or rainbow trout (O. mykiss), and belonging to a host-associated multilocus sequence typing clonal complex (e.g. CC-ST9, CC-ST232 or CC-ST10), were PCR-serotyped, evaluated for proteolytic activity, and used to challenge adipose fin-clipped 4-month old Atlantic salmon, coho salmon and rainbow trout via immersion. Findings showed US87-RBT caused disease and mortality only in rainbow trout (e.g. 56.7% survival probability). US19-COS and US62-ATS caused more mortality in coho salmon and Atlantic salmon but also caused disease in both other host species, albeit to a lesser extent. Observed survival differences may be due to variant antigenic/virulence determinants as differences in serotype and proteolytic activity were discovered. Collectively, results highlight the intricacies of F. psychrophilum-host interactions and provide further in vivo evidence that some F. psychrophilum MLST variants are host specific, which may have implications for the development of BCWD prevention and control strategies.

Influence of pathogens on host genome and epigenome in development of head and neck cancer

BACKGROUND

Head and neck cancer (HNSCC) is a heterogeneous group of cancers, affecting multiple regions such as oral cavity, pharynx, larynx, and nasal region, each showing a distinct molecular profile. HNSCC accounts for more than 6 million cases worldwide, soaring mainly in the developing countries.

RECENT FINDINGS

The aetiology of HNSCC is complex and multifactorial, involving both genetic and environmental factors. The critical role of microbiome, which includes bacteria, viruses, and fungi, is under spotlight due to the recent reports on their contribution in the development and progression of HNSCC. This review focuses on the effect of opportunistic pathogens on the host genome and epigenome, which contributes to the disease progression. Drawing parallels from the host-pathogen interactions observed in other tumour types arising from the epithelial tissue such as colorectal cancer, the review also calls attention to the potential explorations of the role of pathogens in HNSCC biology and discusses the clinical implications of microbiome research in detection and treatment of HNSCC.

CONCLUSION

Our understanding of the genomic effects of the microbes on the disease progression and the mechanistic insights of the host-pathogen interaction will pave way to novel treatment and preventive approaches in HNSCC.

Host genetic variation at a locus near CHD1L impacts HIV sequence diversity in a South African population

IMPORTANCE

It has been previously shown that genetic variants near CHD1L on chromosome 1 are associated with reduced HIV VL in African populations. However, the impact of these variants on viral diversity and how they restrict viral replication are unknown. We report on a regional association analysis in a South African population and show evidence of selective pressure by variants near CHD1L on HIV RT and gag. Our findings provide further insight into how genetic variability at this locus contributes to host control of HIV in a South African population.

Bacterial outer membrane vesicles bound to bacteriophages modulate neutrophil responses to bacterial infection

Pseudomonas aeruginosa is a major human pathogen, particularly effective at colonizing the airways of patients with cystic fibrosis. Bacteriophages are highly abundant at infection sites, but their impact on mammalian immunity remains unclear. We previously showed that Pf4, a temperate filamentous bacteriophage produced by P. aeruginosa, modifies the innate immune response to P. aeruginosa infections via TLR3 signaling, but the underlying mechanisms remained unclear. Notably, Pf4 is a single-stranded DNA and lysogenic phage, and its production does not typically result in lysis of its bacterial host. We identified previously that internalization of Pf4 by human or murine immune cells triggers maladaptive viral pattern recognition receptors and resulted in bacterial persistence based on the presence of phage RNA. We report now that Pf4 phage dampens inflammatory responses to bacterial endotoxin and that this is mediated in part via bacterial vesicles attached to phage particles. Outer membrane vesicles (OMVs) are produced by Gram-negative bacteria and play a key role in host pathogen interaction. Recently, evidence has emerged that OMVs differentially package small RNAs. In this study, we show that Pf4 are decorated with OMVs that remain affixed to Pf4 despite of purification steps. These phages are endocytosed by human cells and delivered to endosomal vesicles. We demonstrate that short RNAs within the OMVs form hairpin structures that trigger TLR3-dependent type I interferon production and antagonize production of antibacterial cytokines and chemokines. In particular, Pf4 phages inhibit CXCL5, preventing efficient neutrophil chemotaxis in response to endotoxin. Moreover, blocking IFNAR or TLR3 signaling abrogates the effect of Pf4 bound to OMVs on macrophage activation. In a murine acute pneumonia model, mice treated with Pf4 associated with OMVs show significantly less neutrophil infiltration in BAL fluid than mice treated with purified Pf4. These changes in macrophage phenotype are functionally relevant: conditioned media from cells exposed to Pf4 decorated with OMVs are significantly less effective at inducing neutrophil migration in vitro and in vivo. These results suggest that Pf4 phages alter innate immunity to bacterial endotoxin and OMVs, potentially dampening inflammation at sites of bacterial colonization or infection.

Research progress of single-cell sequencing in tuberculosis

Tuberculosis is a major infectious disease caused by Mycobacterium tuberculosis infection. The pathogenesis and immune mechanism of tuberculosis are not clear, and it is urgent to find new drugs, diagnosis, and treatment targets. A useful tool in the quest to reveal the enigmas related to Mycobacterium tuberculosis infection and disease is the single-cell sequencing technique. By clarifying cell heterogeneity, identifying pathogenic cell groups, and finding key gene targets, the map at the single cell level enables people to better understand the cell diversity of complex organisms and the immune state of hosts during infection. Here, we briefly reviewed the development of single-cell sequencing, and emphasized the different applications and limitations of various technologies. Single-cell sequencing has been widely used in the study of the pathogenesis and immune response of tuberculosis. We review these works summarizing the most influential findings. Combined with the multi-molecular level and multi-dimensional analysis, we aim to deeply understand the blank and potential future development of the research on Mycobacterium tuberculosis infection using single-cell sequencing technology.

Not only for Christmas: Prophylactic oral application of trans-cinnamaldehyde alleviates acute murine campylobacteriosis

The prevalence of Campylobacter jejuni infections is increasing worldwide and responsible for significant morbidities and socioeconomic expenses. The rise in antimicrobial resistance of C. jejuni underscores the urge for evaluating antibiotics-independent compounds as therapeutic and preventive treatment options of human campylobacteriosis. Given its well-known anti-microbial and immune-modulatory properties we here surveyed the disease-modifying effects of trans-cinnamaldehyde pretreatment in experimental campylobacteriosis. Therefore, secondary abiotic IL-10-/- mice were orally challenged with trans-cinnamaldehyde starting 7 days prior C. jejuni infection. Whereas gastrointestinal colonization properties of the enteropathogens remained unaffected, trans-cinnamaldehyde pretreatment did not only improve clinical signs in infected mice, but also alleviated colonic epithelial cell apoptosis on day 6 post-infection. Furthermore, trans-cinnamaldehyde application resulted in less pronounced T cell responses in the colon that were accompanied by dampened proinflammatory mediator secretion in distinct intestinal compartments. Notably, the immune-modulatory effects of trans-cinnamaldehyde were not restricted to the intestinal tract but could also be observed in extra-intestinal organs such as the liver and kidneys. In conclusion, our preclinical placebo-controlled intervention study provides first evidence that due to its immune-modulatory effects, trans-cinnamaldehyde constitutes a promising prophylactic option to alleviate campylobacteriosis.

Microbiota as key factors in inflammatory bowel disease

Inflammatory Bowel Disease (IBD) is characterized by prolonged inflammation of the gastrointestinal tract, which is thought to occur due to dysregulation of the immune system allowing the host's cells to attack the GI tract and cause chronic inflammation. IBD can be caused by numerous factors such as genetics, gut microbiota, and environmental influences. In recent years, emphasis on commensal bacteria as a critical player in IBD has been at the forefront of new research. Each individual harbors a unique bacterial community that is influenced by diet, environment, and sanitary conditions. Importantly, it has been shown that there is a complex relationship among the microbiome, activation of the immune system, and autoimmune disorders. Studies have shown that not only does the microbiome possess pathogenic roles in the progression of IBD, but it can also play a protective role in mediating tissue damage. Therefore, to improve current IBD treatments, understanding not only the role of harmful bacteria but also the beneficial bacteria could lead to attractive new drug targets. Due to the considerable diversity of the microbiome, it has been challenging to characterize how particular microorganisms interact with the host and other microbiota. Fortunately, with the emergence of next-generation sequencing and the increased prevalence of germ-free animal models there has been significant advancement in microbiome studies. By utilizing human IBD studies and IBD mouse models focused on intraepithelial lymphocytes and innate lymphoid cells, this review will explore the multifaceted roles the microbiota plays in influencing the immune system in IBD.

Cell-type-specific responses to fungal infection in plants revealed by single-cell transcriptomics

Pathogen infection is a dynamic process. Here, we employ single-cell transcriptomics to investigate plant response heterogeneity. By generating an Arabidopsis thaliana leaf atlas encompassing 95,040 cells during infection by a fungal pathogen, Colletotrichum higginsianum, we unveil cell-type-specific gene expression, notably an enrichment of intracellular immune receptors in vasculature cells. Trajectory inference identifies cells that had different interactions with the invading fungus. This analysis divulges transcriptional reprogramming of abscisic acid signaling specifically occurring in guard cells, which is consistent with a stomatal closure dependent on direct contact with the fungus. Furthermore, we investigate the transcriptional plasticity of genes involved in glucosinolate biosynthesis in cells at the fungal infection sites, emphasizing the contribution of the epidermis-expressed MYB122 to disease resistance. This work underscores spatially dynamic, cell-type-specific plant responses to a fungal pathogen and provides a valuable resource that supports in-depth investigations of plant-pathogen interactions.

Advances in understanding the mechanism of resistance to anthracnose and induced defence response in tea plants

The tea plant (Camellia sinensis) is susceptible to anthracnose disease that causes considerable crop loss and affects the yield and quality of tea. Multiple Colletotrichum spp. are the causative agents of this disease, which spreads quickly in warm and humid climates. During plant-pathogen interactions, resistant cultivars defend themselves against the hemibiotrophic pathogen by activating defence signalling pathways, whereas the pathogen suppresses plant defences in susceptible varieties. Various fungicides have been used to control this disease on susceptible plants, but these fungicide residues are dangerous to human health and cause fungicide resistance in pathogens. The problem-solving approaches to date are the development of resistant cultivars and ecofriendly biocontrol strategies to achieve sustainable tea cultivation and production. Understanding the infection stages of Colletotrichum, tea plant resistance mechanisms, and induced plant defence against Colletotrichum is essential to support sustainable disease management practices in the field. This review therefore summarizes the current knowledge of the identified causative agent of tea plant anthracnose, the infection strategies and pathogenicity of C. gloeosporioides, anthracnose disease resistance mechanisms, and the caffeine-induced defence response against Colletotrichum infection. The information reported in this review will advance our understanding of host-pathogen interactions and eventually help us to develop new disease control strategies.

One for all-human kidney Caki-1 cells are highly susceptible to infection with corona- and other respiratory viruses

In vitro investigations of host-virus interactions are reliant on suitable cell and tissue culture models. Results are only as good as the model they are generated in. However, choosing cell models for in vitro work often depends on availability and previous use alone. Despite the vast increase in coronavirus research over the past few years, scientists are still heavily reliant on: non-human, highly heterogeneous or not fully differentiated, or naturally unsusceptible cells requiring overexpression of receptors and other accessory factors. Complex primary or stem cell models are highly representative of human tissues but are expensive and time-consuming to develop and maintain with limited suitability for high-throughput experiments.Using tissue-specific expression patterns, we identified human kidney cells as an ideal target for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and broader coronavirus infection. We show the use of the well-characterized human kidney cell line Caki-1 for infection with three human coronaviruses (hCoVs): Betacoronaviruses SARS-CoV-2 and Middle Eastern respiratory syndrome coronavirus and Alphacoronavirus hCoV 229E. Caki-1 cells show equal or superior susceptibility to all three coronaviruses when compared to other commonly used cell lines for the cultivation of the respective virus. Antibody staining against SARS-CoV-2 N protein shows comparable replication rates. A panel of 26 custom antibodies shows the location of SARS-CoV-2 proteins during replication using immunocytochemistry. In addition, Caki-1 cells were found to be susceptible to two other human respiratory viruses, influenza A virus and respiratory syncytial virus, making them an ideal model for cross-comparison for a broad range of respiratory viruses. IMPORTANCE Cell lines remain the backbone of virus research, but results are only as good as their originating model. Despite increased research into human coronaviruses following the COVID-19 pandemic, researchers continue to rely on suboptimal cell line models of: non-human origin, incomplete differentiation, or lacking active interferon responses. We identified the human kidney Caki-1 cell line as a potential target for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). This cell line could be shown to be infectable with a wide range of coronaviruses including common cold virus hCoV-229E, epidemic virus MERS-CoV, and SARS-CoV-2 as well as other important respiratory viruses influenza A virus and respiratory syncytial virus. We could show the localization of 26 SARS-CoV-2 proteins in Caki-1 cells during natural replication and the cells are competent of forming a cellular immune response. Together, this makes Caki-1 cells a unique tool for cross-virus comparison in one cell line.

Extracellular vesicles biogenesis and uptake concepts: A comprehensive guide to studying host-pathogen communication

The study of host-pathogen interactions has increased considerably in recent decades. This intercellular communication has been mediated by extracellular vesicles (EVs) that play an important role during the interaction. EVs are particles of lipid bilayer and described in different types of cells, eukaryotic or prokaryotic. Depending on their biogenesis they are described as exosomes (derived from multivesicular bodies) and microvesicles (derived from the plasma membrane). The EVs carry biomolecules, including nucleic acids, lipids, and proteins that can be released or internalized by other cells in different pathways (endocytosis, macropinocytosis, phagocytosis, or membrane fusion) in the process described as uptake. The balance between biogenesis and uptake of EVs could modify physiological and pathophysiological processes of the cell. This review is focusing on the dynamic roles of release and capture of EVs during host-pathogen interaction. We also do a critical analysis of methodologies for obtaining and analyzing EVs. Finally, we draw attention to critical points to be considered in EV biogenesis and uptake studies.

Airway epithelial cells mount an early response to mycobacterial infection

Lung epithelial cells represent the first line of host defence against foreign inhaled components, including respiratory pathogens. Their responses to these exposures may direct subsequent immune activation to these pathogens. The epithelial response to mycobacterial infections is not well characterized and may provide clues to why some mycobacterial infections are cleared, while others are persistent and pathogenic. We have utilized an air-liquid interface model of human primary bronchial epithelial cells (ALI-PBEC) to investigate the epithelial response to infection with a variety of mycobacteria: Mycobacterium tuberculosis (Mtb), M. bovis (BCG), M. avium, and M. smegmatis. Airway epithelial cells were found to be infected by all four species, albeit at low frequencies. The proportion of infected epithelial cells was lowest for Mtb and highest for M. avium. Differential gene expression analysis revealed a common epithelial host response to mycobacteria, including upregulation of BIRC3, S100A8 and DEFB4, and downregulation of BPIFB1 at 48 h post infection. Apical secretions contained predominantly pro-inflammatory cytokines, while basal secretions contained tissue growth factors and chemokines. Finally, we show that neutrophils were attracted to both apical and basal secretions of infected ALI-PBEC. Neutrophils were attracted in high numbers to apical secretions from PBEC infected with all mycobacteria, with the exception of secretions from M. avium-infected ALI-PBEC. Taken together, our results show that airway epithelial cells are differentially infected by mycobacteria, and react rapidly by upregulation of antimicrobials, and increased secretion of inflammatory cytokines and chemokines which directly attract neutrophils. Thus, the airway epithelium may be an important immunological component in controlling and regulating mycobacterial infections.

Role of Legionella pneumophila outer membrane vesicles in host-pathogen interaction

Legionella pneumophila is an opportunistic intracellular pathogen that inhabits artificial water systems and can be transmitted to human hosts by contaminated aerosols. Upon inhalation, it colonizes and grows inside the alveolar macrophages and causes Legionnaires' disease. To effectively control and manage Legionnaires' disease, a deep understanding of the host-pathogen interaction is crucial. Bacterial extracellular vesicles, particularly outer membrane vesicles (OMVs) have emerged as mediators of intercellular communication between bacteria and host cells. These OMVs carry a diverse cargo, including proteins, toxins, virulence factors, and nucleic acids. OMVs play a pivotal role in disease pathogenesis by helping bacteria in colonization, delivering virulence factors into host cells, and modulating host immune responses. This review highlights the role of OMVs in the context of host-pathogen interaction shedding light on the pathogenesis of L. pneumophila. Understanding the functions of OMVs and their cargo provides valuable insights into potential therapeutic targets and interventions for combating Legionnaires' disease.

Transcriptomic Analysis of Metarhizium anisopliae-Induced Immune-Related Long Non-Coding RNAs in Polymorphic Worker Castes of Solenopsis invicta

Long non-coding RNAs (lncRNAs) represent a class of RNA molecules that do not encode proteins. Generally studied for their regulatory potential in model insects, relatively little is known about their immunoregulatory functions in different castes of eusocial insects, including Solenopsis invicta, a notoriously invasive insect pest. In the current study, we used Metarhizium anisopliae, an entomopathogenic fungus, to infect the polymorphic worker castes (Major and Minor Workers) and subjected them to RNA sequencing at different intervals (6, 24, and 48 h post-infection (hpi)). Comprehensive bioinformatic analysis identified 5719 (1869 known and 3850 novel) lncRNAs in all libraries. Genomic characteristics analysis showed that S. invicta lncRNAs exhibited structural similarities with lncRNAs from other eusocial insects, including lower exon numbers, shorter intron and exon lengths, and a lower expression profile. A comparison of lncRNAs in major and minor worker ants revealed that several lncRNAs were exclusively expressed in one worker caste and remained absent in the other. LncRNAs such as MSTRG.12029.1, XR_005575440.1 (6 h), MSTRG.16728.1, XR_005575440.1 (24 h), MSTRG.20263.41, and MSTRG.11994.5 (48 h) were only present in major worker ants, while lncRNAs such as MSTRG.8896.1, XR_005574239.1 (6 h), MSTRG.20289.8, XR_005575051.1 (24 h), MSTRG.20289.8, and MSTRG.6682.1 (48 h) were only detected in minor workers. Additionally, we performed real-time quantitative PCR and experimentally validated these findings. Functional annotation of cis-acting lncRNAs in major worker ants showed that lncRNAs targeted genes such as serine protease, trypsin, melanization protease-1, spaetzle-3, etc. In contrast, apoptosis and autophagy-related genes were identified as targets of lncRNAs in minor ants. Lastly, we identified several lncRNAs as precursors of microRNAs (miRNAs), such as miR-8, miR-14, miR-210, miR-6038, etc., indicating a regulatory relationship between lncRNAs, miRNAs, and mRNAs in antifungal immunity. These findings will serve as a genetic resource for lncRNAs in polymorphic eusocial ants and provide a theoretical basis for exploring the function of lncRNAs from a unique and novel perspective.

Fungal co-expression network analyses identify pathogen gene modules associated with host insect invasion

The broad host range fungal insect pathogen, Beauveria bassiana, has been commercialized as an alternative to chemical insecticides for pest control worldwide. B. bassiana represents a unique model system with which to examine host-pathogen interactions, and a wide range of genes and processes have been studied. However, significant aspects of virulence, particularly on the genomic scale, remain poorly studied. Here, we have combined available transcriptomes with three newly generated data sets for a combined total analysis of 76 deep-sequenced samples covering growth, development, stress responses, and infection during the life cycle of B. bassiana. Co-expression network analyses resulted in the identification of gene modules enriched during two critical stages of the infection process, namely (i) cuticle penetration and (ii) in vivo hyphal body (dimorphic transition) growth capable of avoiding innate and humoral immune defenses. These analyses identify unique signatures of metabolism, signaling, secondary metabolite production, host defense suppression, membrane reorganization, effector production, and secretion for each stage, including genetic regulators and epigenetic patterns. These data provide a comprehensive framework for understanding and probing fungal adaptations to its pathogenic life cycle and expand the candidate repertoire for continued dissection of the host-pathogen interaction. IMPORTANCE Insect fungal pathogens have evolved unique strategies for overcoming host structural and immunological defenses that span from the sclerotized cuticle to innate and humoral cellular responses. Two critical stages of the infection process involve (i) cuticle penetration and (ii) immune evasion within the insect hemocoel. A set of 76 global transcriptomic data for B. bassiana that include the cuticle penetration and hemocoel growth stages were analyzed for patterns (gene modules) of expression, yielding unique insights into these different life stages. These analyses integrate gene networks involved in fungal development, stress response and pathogenesis to further the systematic understanding of the global processes integral to the unique adaptation employed by fungal pathogens of insects.

Unraveling the Role of the Zinc-Dependent Metalloproteinase/HTH-Xre Toxin/Antitoxin (TA) System of Brucella abortus in the Oxidative Stress Response: Insights into the Stress Response and Virulence

Toxin/antitoxin (TA) systems have been scarcely studied in Brucella abortus, the causative agent of brucellosis, which is one of the most prevalent zoonotic diseases worldwide. In this study, the roles of a putative type II TA system composed by a Zinc-dependent metalloproteinase (ZnMP) and a transcriptional regulator HTH-Xre were evaluated. The deletion of the open reading frame (ORF) BAB1_0270, coding for ZnMP, used to produce a mutant strain, allowed us to evaluate the survival and gene expression of B. abortus 2308 under oxidative conditions. Our results showed that the B. abortus mutant strain exhibited a significantly reduced capacity to survive under hydrogen peroxide-induced oxidative stress. Furthermore, this mutant strain showed a decreased expression of genes coding for catalase (katE), alkyl hydroperoxide reductase (ahpC) and transcriptional regulators (oxyR and oxyR-like), as well as genes involved in the general stress response, phyR and rpoE1, when compared to the wild-type strain. These findings suggest that this type II ZnMP/HTH-Xre TA system is required by B. abortus to resist oxidative stress. Additionally, previous evidence has demonstrated that this ZnMP also participates in the acidic stress resistance and virulence of B. abortus 2308. Therefore, we propose a hypothetical regulatory function for this ZnMP/HTH-Xre TA system, providing insight into the stress response and its potential roles in the pathogenesis of B. abortus.