Infection and Immunity最新文献

Hospital-acquired infections (HAIs) represent a major global health burden, leading to increased patient morbidity, mortality, and healthcare costs. These infections frequently occur following patient contact with microbial pathogens persisting on indwelling devices and other abiotic surfaces in the hospital environment. A key driver of this persistence is the ability to survive the total loss of water, a phenomenon known as desiccation tolerance. While desiccation tolerance has been studied across various kingdoms of life, comparatively little is known about the molecular mechanisms that enable bacterial pathogens to tolerate extreme water loss. In this review, we will examine the consequences of desiccation stress in bacteria and highlight conserved mechanisms by which bacterial cells tolerate drying, including spore formation, capsule synthesis, osmolyte accumulation, expression of intrinsically disordered proteins, and other protective mechanisms. We will also examine the mechanisms and consequences of desiccation tolerance in several clinically significant nosocomial pathogens and review emerging evidence that desiccation stress responses may influence other bacterial traits, such as antimicrobial resistance, polymicrobial community interactions, and virulence. Understanding the mechanisms by which nosocomial pathogens tolerate desiccation may reveal novel strategies to disrupt pathogen reservoirs and reduce future HAI transmission.

The serine/threonine protein kinase F (PknF) of Mycobacterium tuberculosis (Mtb) has poorly defined targets and functions but is involved in limiting NLRP3 inflammasome activation in murine macrophages and dendritic cells in vitro. The importance of PknF for the virulence of Mtb in vivo is not known. Here, we demonstrate that the Mtb CDC1551 deletion mutant of pknF (∆pknF) expresses significantly increased levels of the lipid pthiocerol dimycoserosate (PDIM), a polyketide lipid with pro-virulence properties. The ∆pknF mutant strain compared with the Mtb and complemented strains showed a 100-fold increase in growth at day 28 and about a 10-fold increase in growth at days 90-98 in the lungs of mice. The increase in pulmonary bacterial loads after infection with the ∆pknF strain was conserved even in Nlrp3-deficient mice, arguing that PknF modulates Mtb virulence independently of NLRP3-inflammasome activation in mice. Staining of lung sections revealed increased inflammation in the lungs of ∆pknF strain-infected mice when compared with Mtb and the complemented mutant strain. Highly susceptible B6.Sst1^S mice displayed decreased host resistance, with significantly decreased survival when infected with the ∆pknF strain compared to the complemented strain or Mtb. In conclusion, our data suggest that expression of PknF, as a modulator of multiple downstream effector proteins, restricts the virulence of Mtb in the lungs of mice through an NLRP3 inflammasome-independent mechanism, but potentially via suppressing production of the virulence lipid, PDIM.

Cryptococcal meningoencephalitis is among the most prevalent invasive fungal diseases, posing a threat to immunocompromised individuals and representing a growing global health concern. The mechanisms of cryptococcal trafficking of virulence factors during disease are incompletely understood. Adaptor protein (AP) complexes play crucial roles in intracellular trafficking by orchestrating the sorting of macromolecular cargo and serving as essential components of the endocytic and secretory pathways. In a recent study, we demonstrated that Cryptococcus neoformans cells lacking the AP-1 complex subunits exhibit impaired elaboration of virulence factors and fail to survive in the harsh conditions of the macrophage phagolysosome. Although we characterized the phenotypes of AP-1 deficient cells in vitro, the contribution of this complex to pathogenesis remains unexplored. In this study, we show that mutants deficient in AP-1 complex subunits are either avirulent or exhibit attenuated virulence in a murine inhalational model. Loss of the small subunit resulted in the formation of granuloma-like lesions in mouse lungs with early containment of infection but eventual mortality, whereas mutants lacking the large subunits were rapidly cleared by mice. The delayed onset of disease in mice caused by mutants lacking the small subunit was marked by delayed weight loss and increased respiration rate, yet the mutant exhibited enhanced dissemination during late-stage infection, coinciding with waning immune responses and elevated collagen deposition. These findings demonstrate that deficiencies in the AP-1 complex impair C. neoformans virulence, reveal distinct roles for individual subunits, and identify the complex as a potential target for therapeutic intervention in cryptococcosis.

Recently approved malaria pre-erythrocytic vaccines are important public health tools for the reduction of malaria morbidity and mortality. However, these vaccines have shown reduced protection in some of the most vulnerable age groups, require multiple dosing, and have the potential for parasite escape. These limitations have motivated the development of vaccines targeting multiple stages of the parasite life cycle. To ensure a robust pipeline, pre-clinical evaluation of additional malaria vaccine candidate antigens remains a key priority. The P. falciparum cysteine protease inhibitor falstatin can limit the cysteine protease activity of falcipains, controlling proteolysis at the site of merozoite entry on erythrocytes, thereby facilitating parasite invasion. Antibodies against falstatin have been shown to reduce the ability of merozoites to invade erythrocytes, raising the possibility that naturally acquired antibody responses could confer a similar advantage to the host. Here, IgG responses to full-length falstatin (falstatin_FL) and two smaller, conserved regions (falstatin_35-68 and falstatin_289-335) were determined at the pre-malaria season baseline in a prospective cohort study conducted in Kalifabougou, Mali. The presence of anti-falstatin IgG was not associated with reduced risk of clinical malaria overall. However, baseline falstatin seropositivity predicted a non-statistically significant reduction in risk of febrile malaria within the first 30 days after incident parasitemia (log-rank statistic 3.2, P = 0.072). Using in vitro growth inhibitory assays, neither affinity-purified anti-falstatin_289-335 IgG nor affinity-purified anti-falstatin_FL IgG consistently inhibited P. falciparum blood-stage parasites. Larger cohort studies would be needed to confirm whether pre-existing anti-falstatin antibodies can delay the progression of malaria symptoms after blood-stage infection.

Lipopolysaccharide (LPS) is a major outer membrane component of Gram-negative bacteria that can modulate host immune responses during infection. Extensive studies on the LPS of well-studied organisms, such as Escherichia coli and Salmonella spp., have elucidated many LPS pathways; however, knowledge of unique LPS structures of lesser-studied bacteria, such as Coxiella burnetii, remains limited. C. burnetii is an intracellular pathogen that is the cause of the zoonotic disease Q fever. The highly infectious nature of C. burnetii warrants designation as a select agent by the United States Federal Select Agent Program and must be contained in a Biosafety Level three facility. Contributing to the organism's biothreat potential, C. burnetii LPS is a critical virulence determinant that dictates bacterial survival and pathogenesis. Several reviews have extensively covered C. burnetii LPS structure and function prior to 2017, though recent findings regarding mechanisms of LPS biosynthesis, LPS-induced host immunity, and LPS elongation pose biosafety and regulatory questions that necessitate careful consideration. Here, we discuss recent (post-2017) findings related to C. burnetii LPS from scientific and biosafety perspectives that may be applicable across many fields of research. From the discovery of C. burnetii LPS phase variation by Fiset and Stoker in 1956 to the recent elucidation of specific genetic mechanisms underlying this process, the study of C. burnetii LPS is a reminder that what goes around comes around, even in research.

The high virulence and pathogenesis of Francisella tularensis (Ft), responsible for tularemia, made it a target for bioweapon development during the "Cold War." This prompted investigation of vaccines, starting with an older vaccine candidate denoted Ft live vaccine strain (LVS). LVS has limited efficacy against aerosol challenge with Ft subsp. Tularensis (Type A), the most virulent subtype. However, no vaccines, including LVS, have been licensed in the U.S. Animal studies indicate that Ft vaccines induce protective T-cell-mediated immune responses. In previous studies, analyses of leukocytes from vaccinated animals that were restimulated in vitro facilitated screening and selection of vaccines for more extensive in vivo evaluation. These studies demonstrated that a novel live attenuated vaccine strain derived from Type A Ft, denoted ΔclpB, was protective against aerosol challenge in animal models. In this study, we focused on evaluating immune responses immediately after vaccination of Fischer 344 rats with LVS and ΔclpB using multiple analytical approaches. While humoral immune responses were comparable between the two vaccines, we identified multiple differences in immune responses by analyses of peripheral blood leukocytes by flow cytometry and by relative gene expression. In particular, vaccination with LVS or ΔclpB resulted in differential expression of multiple genes at selected time points. Gene expression, in turn, predicted activation or inhibition of multiple biological pathways. These results suggest that immune responses shortly after primary vaccination may discriminate vaccines with different degrees of in vivo protection that could potentially be used as correlates of protection and extrapolate efficacy from animals to people.

Competition between organisms is a ubiquitous feature of life on Earth and a major driver of evolutionary innovation. As Earth's most diverse and abundant organisms, bacteria employ numerous strategies to inhibit the growth of competitors, ranging from the production of diffusible antibiotic metabolites to the secretion of sophisticated protein toxins. Although secreted antibacterial protein toxins have been extensively studied in gram-negative bacteria, analogous systems employed by gram-positive organisms remain comparatively poorly understood. Recent work has shed light on a widespread family of secreted protein toxins associated with co-secreted serine proteases that likely mediate interbacterial competition among gram-positive species. These systems, termed antibacterial protein (ABP) systems, consist of a secreted polymorphic toxin (AbpT), a co-secreted serine protease (AbpP), and a cytoplasmic immunity protein (AbpI). Following proteolytic processing, ABP toxins inhibit the growth of a remarkably diverse range of gram-positive bacteria spanning the phyla Bacillota and Actinomycetota. Existing evidence suggests that these proteins combine the properties of cationic antimicrobial peptides with those of classical polymorphic antibacterial toxins, potentially enabling toxin delivery into distantly related bacteria. In this review, we summarize the current understanding of the organization, mechanisms, and ecology of ABP systems; discuss major outstanding questions regarding toxin import and native biological function; and highlight opportunities for future mechanistic and biotechnological investigation in this emerging field.

The vaginal microbiome is an important aspect of female reproductive health. The dominant microbial species of this ecosystem, Lactobacillus, offers protection from vaginal infections by maintaining lower pH levels and reducing potential pathogen colonization. Dysbiosis, or imbalance of the vaginal microbial ecosystem, has been associated with both common infections, such as bacterial vaginosis (BV), vulvovaginal candidiasis (VVC), and urinary tract infections (UTIs), and obstetric complications, including gestational diabetes, preterm labor, and obstetric anemia. This review provides an overview of the composition and function of the vaginal microbiota, emphasizing the role of Lactobacillus and other beneficial microbes and their mechanisms of action, including lactic acid and hydrogen peroxide production, competitive adherence, and immune modulation. Evidence from clinical trials supports the efficacy of these strains in reducing recurrence of BV, VVC, and UTIs. Additionally, emerging research shows promise for probiotic use in managing reproductive conditions such as gestational diabetes mellitus, preterm labor, and obstetric anemia. The review also discusses safety considerations, particularly in immunocompromised individuals, and the expanding interest in non-Lactobacillus genera like Bifidobacterium and Bacillus. Targeted probiotic interventions have great potential for restoring and maintaining a healthy vaginal microbiome, preventing recurrent infections, and helping improve reproductive outcomes. However, in order to incorporate these approaches in clinical practice, probiotic strains, delivery method, and dosage all need standardization.

Porphyromonas gingivalis is an oral bacterium commonly associated with periodontitis. P. gingivalis synthesizes sphingolipids (SLs), and recently, we reported that P. gingivalis SLs packaged into outer membrane vesicles (OMVs) can regulate THP-1 macrophage inflammatory responses to P. gingivalis OMVs. The contribution that P. gingivalis SLs have on host-pathogen interactions remains poorly understood, especially in the context of OMVs. Here, we demonstrate that P. gingivalis SLs significantly reduce the uptake of OMVs isolated from SL-containing wild-type (WT) P. gingivalis compared to OMVs from an SL-null mutant P. gingivalis strain, and that the loss of SLs drives uptake of P. gingivalis OMVs via lipid rafts in THP-1 macrophages. Intriguingly, we found that the sensing of P. gingivalis OMVs via TLR2 and MyD88 is attenuated due to the presence of SLs. Lastly, transcriptomic analysis of THP-1 macrophages co-cultured with either WT or SL-null P. gingivalis OMVs for 2 h revealed an array of differentially expressed genes. Interestingly, at 2 h, WT P. gingivalis OMVs promoted an overall trend of gene downregulation in THP-1 macrophages when compared to unchallenged, whereas SL-null OMVs strongly promoted upregulated gene expression. These findings provide early-phase characterization of the role of SLs in initial host cellular responses to P. gingivalis OMVs and expand our knowledge of interactions between SL-containing P. gingivalis OMVs and the host.

The severity of Clostridioides difficile infection is dictated by a complex interplay of various host cell types and inflammatory mediators responding to the pathogen and surrounding microbiome. An effective immune response must carefully balance controlling C. difficile-mediated pathology and systemic dissemination of opportunistic bacteria while avoiding collateral immunopathology. In addition, a successful immune response must also promote restorative mechanisms to repair toxin-induced disruptions to the intestinal barrier. Here, we review the immune response to C. difficile infection with a specific focus on the role of innate immune-induced cytokines.