Infection and Immunity最新文献

Coxiella burnetii is an obligate intracellular bacterial pathogen that causes the zoonotic disease Q fever. Coxiella extensively subverts host vesicle traffic and replicates within lysosome-derived, spacious vacuoles by secreting a suite of effectors through the type IVB secretion system (T4BSS). This study investigates the regulation and role of a fundamental lysosomal process, exocytosis, in the prolonged maintenance of Coxiella vacuolar niche. Biochemical, microscopic, and proteomic approaches indicate that infection promotes release of extracellular vesicles (EVs). Increase in extracellular levels of endolysosomal proteins and surface localization of LAMP1 were identified in both phagocytic and non-phagocytic cells, during later stages of infection. Interestingly, infection-induced exocytosis was dependent on the activity of the bacterial T4BSS. On one hand, knockdown of the lysosomal master transcriptional regulator TFEB significantly reduces basal exocytosis and enhances intracellular Coxiella replication, while deficiency of the exocytosis-associated SNARE, Syntaxin 11, does not reduce basal exocytosis and yet, increases Coxiella replication, suggesting that host exocytosis is not the sole or a dominant determinant of the infection process. On the other hand, modulating the activity of a key host exocytosis regulator- the calcium channel TRPML1, decreases intracellular Coxiella replication suggesting a tightly regulated role of TRPML1. Infection was also associated with the extracellular detection of LAMP1-associated Coxiella, suggesting an encased egress mechanism. Together, this study demonstrates that Coxiella infection activates exocytosis in a temporal, host-, and bacterial factor-dependent manner.

Enteric viruses are major causes of gastrointestinal disease worldwide and are primarily transmitted through the fecal-oral route. Upon entering the gastrointestinal tract, these viruses encounter the dense and diverse population of intestinal microbiota, leading to frequent interactions with commensal bacteria. Over the past decade, numerous studies have demonstrated that bacteria can enhance enteric viral replication, stability, and overall pathogenesis. Although direct binding interactions between enteric viruses and bacteria have been observed, the molecular determinants governing these interactions remain poorly understood. Defining the viral and bacterial factors that mediate binding is, therefore, critical for understanding how bacteria can influence viral infection, transmission, and disease. Here, in this minireview, we summarize the current findings on enteric viral-bacterial interactions, with a focus on the mechanisms of viral binding to bacteria and the implications of these interactions on enteric virus pathogenesis and transmission.

Iron and oxygen availability fluctuate spatially across mammalian tissues as well as temporally during bacterial infection. The [2Fe-2S] cluster-coordinating transcription factor IscR senses changes in iron and oxygen levels and plays a pivotal role in how Yersinia, Salmonella, and Vibrio regulate critical virulence genes, like the type III secretion system (T3SS). We previously showed that clusterless apo-IscR promotes expression of the Yersinia pseudotuberculosis T3SS master regulator LcrF by binding a type 2 IscR-binding motif in the lcrF promoter, thereby facilitating T3SS expression and disseminated infection. Here, we sought to address how IscR ligation of its [2Fe-2S] cluster impacts LcrF expression and bacterial virulence. We engineered a Y. pseudotuberculosis mutant strain with its native type 2 IscR-binding motif swapped with a type 1 motif that binds [2Fe-2S]-IscR but not apo-IscR. This lcrF^pType1 mutant hyperexpressed LcrF and T3SS-associated proteins in iron-replete anaerobic conditions that favor [2Fe-2S]-IscR. To understand the consequence of this dysregulated expression, we used barcoded Y. pseudotuberculosis libraries to probe infection dynamics of the WT and lcrF ^pType1 mutant strains following oral infection of mice. The lcrF^pType1 mutant experienced altered colonization bottleneck and dissemination patterns compared to WT Yersinia, suggesting that expressing LcrF and T3SS genes in response to [2Fe-2S]-IscR rather than apo-IscR may alter infection dynamics.

For all pathogenic microbes, metabolic processes are essential for growth, development, and survival during infection. However, host niches are dynamic environments where nutrient availability can vary, and host defense mechanisms often restrict access to host-derived nutrients. Therefore, microbes must adapt to these microenvironments by regulating nutrient acquisition and metabolism, and by employing mechanisms such as virulence factors that release host-derived nutrients. This metabolic plasticity is a key feature that enables certain microbes to thrive during host-microbe interactions. Hence, metabolism is essential for fungal virulence; however, the mechanisms by which carbon and nitrogen sources directly modulate virulence remain underexplored. Moreover, much remains to be learned about fungal species and host species specificity. In this review, we discuss the links between carbon and nitrogen metabolism and fungal virulence in human-pathogenic fungi, highlighting the roles of different nutrient types within the host and their influence on fungal virulence. Understanding fungal physiology could help to develop new strategies to control fungal disease.

It is well established that within a bacterial species, genotypic and phenotypic variation leads to differences in virulence, antibiotic susceptibility, and metabolism. However, there is also increasing evidence that often multiple variants of the same species co-inhabit the same site in the human body, both during health and disease. This within-host microdiversity can develop over time for pathogens in chronic infections and has been observed for many members of the microbiota, for instance in the gut and on the skin. Research is just beginning to uncover how this within-host intra-species diversity develops and why it matters. Intra-species diversity is largely stable over time, with occasional selective sweeps of new genotypes, and the overall level of diversity is modulated by both microbe-microbe and microbe-host interactions. Furthermore, data indicate that within-host microdiversity can impact the stability of bacterial communities, their antimicrobial resistance, and the efficacy of probiotics and microbiota transplants. Here, we describe the evolutionary and ecological processes that promote high or low within-host microdiversity and the extent of this diversity in the human microbiota and in infections. In addition, we consider how microdiversity within individuals shapes the functional role of the human microbiota and the progression of disease. Together, within-host microdiversity is a newly developing way to think about the diversity of human-associated microbes, with implications in how we treat chronic infections and manipulate our microbiota to promote health.

Urinary tract infections (UTIs) are a significant public health burden that impact millions of people every year and are highly prevalent among hospital-acquired infections. Klebsiella pneumoniae is globally the second most common cause of UTIs after uropathogenic Escherichia coli (UPEC). Thus far, the molecular mechanisms underlying pathogenesis are better understood in UPEC than in K. pneumoniae. UPEC is known to have virulence phenotypes such as fimbrial adhesion and evasion of complement-mediated killing. In other infection types, K. pneumoniae fitness has been associated with mucoidy and diverse capsular serotypes. To establish K. pneumoniae virulence phenotypes contributing to UTI, we examined how environmental cues regulate urovirulence-associated phenotypes in clinical K. pneumoniae UTI strains. These phenotypes included capsular polysaccharide properties, hemagglutination, serum resistance, adherence to bladder epithelial cells, and in vivo fitness. We found that clinical K. pneumoniae UTI isolates' phenotypes are highly heterogeneous and can change in response to human urine. Despite K. pneumoniae clinical isolates presenting heterogeneous fitness properties, all similarly colonize the urinary tract. These results suggest that additional fitness factors contribute to K. pneumoniae uropathogenesis. Identifying these shared fitness factors will provide mechanistic insights into Klebsiella uropathogenesis and reveal candidate therapeutic targets.

In polymicrobial infections, how the host recognizes and responds to pathogens influences which species will persist to cause chronic infections. The human respiratory tract is a common anatomical site for viral-bacterial co-infections, where primary viral infections predispose to secondary bacterial infections, leading to increased morbidity and mortality. Additionally, co-infections are disproportionately prevalent in people with chronic lung diseases, such as chronic obstructive pulmonary disease and cystic fibrosis. We previously reported that primary viral infections and antiviral interferon (IFN) signaling stimulate Pseudomonas aeruginosa biofilm formation on airway epithelial cells (AECs). IFN signaling induces aerobic glycolysis in AECs and generates lactate as a cellular byproduct. Given that innate immune systems play an integral role in co-infection dynamics, we investigated the role of host-secreted metabolites (i.e., lactate) on innate immune cell activity during respiratory co-infections. We found that exposure to the apical secretions from IFNβ-treated AECs significantly compromised macrophage antibacterial activity, with the soluble metabolite lactate playing an important role. Macrophages used monocarboxylate transporters (MCTs) and G-protein receptors to transport and/or sense lactate, respectively, and this exposure to lactate diminished their bacterial-killing activity in a time exposure-dependent manner. Lactate exposure particularly reprogrammed macrophage cellular metabolism toward a metabolically uncoupled state by increasing oxidative phosphorylation, fatty acid oxidation, and downregulating the proinflammatory antimicrobial functions. Collectively, these findings provide insights into metabolites as complex regulators of trans-kingdom interactions and epithelial-macrophage crosstalk during respiratory co-infections.

Mycoplasma gallisepticum (MG) causes chronic respiratory disease, which is thought to be contributed to by its capacity to evade the immune response of infected birds. It possesses multiple copies of the genes encoding the mycoplasma immunoglobulin binding-protease (MIB-MIP) system, which binds and cleaves avian immunoglobulins (Igs), but also encodes homologs of the Ig-binding Protein-M of M. genitalium and M. pneumoniae and the Ig-cleaving CysP of M. synoviae. However, the interactions between these homologs, their host-specificity, and their interplay with the MIB-MIP system have not been defined. Here, the putative Protein-M and CysP in MG were expressed as recombinant glutathione-S-transferase (GST)-fusion proteins, functionally characterized, and their interactions with different MIB-MIP system components, as well as their impact on antibody-dependent complement-mediated killing of MG, examined. GST-Protein-M bound avian and mammalian immunoglobulins, but did not interact with the MIP proteases. GST-CysP selectively cleaved free chicken IgY and IgY complexed with GST-MIB or GST-Protein-M. GST-Protein-M, GST-CysP, and GST-MIB-MIP proteins all bound ATP, but only GST-CysP had ATPase activity. Sera from MG-infected chickens contained antibodies against a subset of MIP proteins, but not antibodies against Protein-M or CysP. The capacity of rabbit anti-MG antibodies to enhance complement-mediated killing of MG was inhibited by GST-MIB-MIP and GST-Protein-M. GST-CysP could not cleave rabbit IgG and had no detectable effect in the antibody-dependent complement-mediated killing assays. Collectively, these findings establish that Protein-M and CysP function as additional Ig-targeting systems in M. gallisepticum alongside the MIB-MIP system through distinct but complementary mechanisms, enhancing immune evasion and persistence of this important pathogen.

Staphylococcus aureus deploys an arsenal of secreted proteases to remodel the host environment during infection. While traditional substrate-by-substrate characterization has revealed critical host proteins under protease modulation, these conventional strategies cannot reveal the full scope of proteolytic activity occurring at the host-pathogen interface. Degradomic and N-terminomic technologies have begun to bridge this gap by enabling an unbiased, global mapping of protease-generated neo-N-termini across complex host tissues and cell proteomes. Recent work applying these tools to define discrete S. aureus protease pathodegradomes has propelled the field toward a system-level understanding of proteolytic activity. In this minireview, we highlight how terminal amine isotopic labeling of substrates and a newer methodology, terminal amine guanidination of substrates-charge reversal, have captured a deeper understanding of the V8 protease and how this enzyme can dismantle host immune defenses and engender disease. These techniques offer a powerful framework for the future in characterizing the substrate repertoires of other S. aureus secreted proteases, such as aureolysin, staphopain A and B, and the Spls. Furthermore, these advances demonstrate the applicability of degradomic profiling to diverse infection niches, revealing previously unrecognized roles for proteolytic activity in varying host contexts. Finally, we consider how this comprehensive understanding of S. aureus protease activity can inform clinical applications such as protease inhibitor design, host-directed therapies, and pathodegradome-based diagnostics.