Infection and Immunity最新文献

Streptococcus gordonii is a commensal bacterium in the oral cavity and has many surface adhesins that have been well characterized. SspA/B belongs to the Antigen I/II-like family of proteins, which are well known for their multifunctional adherence capabilities. Most AgI/II-like proteins adhere to salivary agglutinin (also known as glycoprotein 340, Gp340). In an effort to identify the putative binding site on the AgI/II-like family of proteins, we conducted structural studies to determine the V-domain of SspB. In this paper, we report the structure of SspB's V-domain in complex with a TEV-peptide that was inserted to cleave the histidine tag at the C-terminus after purification. This peptide shared sequence and structural homology with a helical region on the scavenger receptor cysteine-rich (SRCR) domain of Gp340. Our studies with the synthetic peptide PepCD1^SRCR show that it inhibits the Streptococcus mutans biofilm formation in a dose-dependent manner. A comprehensive comparative analysis of this site with the corresponding sites in the homologous V-domains of S. mutans AgI/II and GbpC established that most of these interface residues were conserved. Based on the structural data, mutational analysis was initiated to study the effect of binding-interface residues on the ability of each of these V-domains from S. mutans and S. gordonii to adhere to salivary agglutinin. Here, we report for the first time the binding site for the V-regions that are distinct among oral streptococci, which provides potential opportunities for therapeutic intervention of pathogenic species.

Cryptosporidium is a protozoan parasite that causes cryptosporidiosis, an enteric infection associated with diarrhea, malnutrition, and impaired childhood development in low- and middle-income countries. Both humoral and cell-mediated immune responses have been implicated in protection, but the durability and quality of human immune responses in immunocompetent adults remain poorly defined. We investigated the development of immunity in two healthy U.S. adults following primary cryptosporidiosis acquired during travel to Bangladesh. Longitudinal plasma samples were analyzed for antibody responses to Cryptosporidium antigens Cp17 and Cp23 and for circulating cytokine profiles. Circulating antibody peaked at 3 weeks post-infection but declined rapidly thereafter, approaching baseline within 16 weeks. In contrast, antibody avidity increased steadily over time, consistent with ongoing affinity maturation in germinal centers. While affinity maturation occurred, the composition of memory B cells specific to Cryptosporidium antigens was skewed toward IgM+ cells across time points, suggesting extrafollicular responses dominated and germinal center-derived, class-switched memory was limited. Cytokine profiling revealed an acute Th1-skewed response, with elevations in CXCL9, CXCL10, IL-27, IFNγ, IL-12, and IL-18 during early infection. These signatures mirrored protective pathways identified in murine models, underscoring the importance of type I immunity in parasite clearance. Together, these findings highlight that while antibody responses to Cryptosporidium are short-lived, avidity maturation persists, and Th1-driven cytokine responses dominate during acute infection. This work provides rare longitudinal data on immune responses in naïve adults following natural cryptosporidiosis and offers insight into mechanisms that may inform vaccine development and strategies to mitigate recurrent infection in vulnerable populations.

Klebsiella pneumoniae is an opportunistic Gram-negative pathogen and a common cause of antibiotic-resistant infections including neonatal sepsis and hospital-acquired pneumonia. K. pneumoniae strains can be categorized into two pathotypes: classical K. pneumoniae (cKp), which often causes nosocomial infections, and hypervirulent K. pneumoniae (hvKp), which can cause severe disease in healthy hosts. New therapies are urgently needed for these infections, and caseinolytic proteins have emerged as promising therapeutic targets in other bacterial pathogens. ClpX and ClpP have been implicated in bacterial protein homeostasis, regulation of virulence, and antimicrobial susceptibility in other species, but their specific roles in K. pneumoniae pathogenesis have yet to be defined. Here, we investigate the contribution of K. pneumoniae ClpX and ClpP to lung infection, virulence factor regulation, and antibiotic susceptibility. In a murine pneumonia model, loss of ClpX impairs infection of both hvKp and cKp. Loss of ClpX results in decreased capsule production in hvKp and enhances type 1 pilus production in both pathotypes. In hvKp, loss of ClpX increases type 3 pili, while in cKp, increased type 3 piliation is observed with loss of ClpP. Across both pathotypes, loss of ClpX or ClpP increases susceptibility to a range of antibiotics. These data identify ClpX as critical to K. pneumoniae virulence and antimicrobial susceptibility. By connecting ClpX to capsule production, pili regulation, and in vivo virulence, this work highlights a conserved putative therapeutic target that may enable adjunctive strategies to enhance antibiotic efficacy or attenuate the severity of K. pneumoniae infection.IMPORTANCEKlebsiella pneumoniae is a leading cause of antibiotic-resistant and hospital-acquired infections. The emergence of highly virulent strains of K. pneumoniae capable of causing severe disease is of utmost concern. Here, we investigate two specific caseinolytic proteins, ClpX and ClpP, produced by both classical and hypervirulent strains of K. pneumoniae and their role in K. pneumoniae lung infection. We show that ClpX is a key regulator of virulence factors including bacterial pili and capsule; it is essential for murine pulmonary fitness across both classical and hypervirulent pathotypes. Furthermore, loss of ClpX increases susceptibility to multiple antibiotics, indicating a role in both protein homeostasis and pathogenicity. These findings suggest ClpX is a conserved virulence determinant in multiple strains of K. pneumoniae and highlight its potential as a therapeutic target to enhance antibiotic efficacy or mitigate disease severity.

Metabolic adaptation to the host environment is a key determinant of bacterial pathogenesis, enabling both colonization and invasive disease. This is particularly true for Neisseria gonorrhoeae (Gc), the causative agent of gonorrhea, which lacks effector-injecting secretion systems or toxins. Gc infection triggers a rapid influx of neutrophils (polymorphonuclear cells [PMNs) that typically kill bacteria through multiple mechanisms, including a potent oxidative burst. Despite this, Gc exhibits remarkable resistance to reactive oxygen species and readily replicates in the presence of PMNs, which is in part due to the consumption of PMN-derived lactate. Previous studies demonstrated that the lactate permease, LctP, is required for oxidative stress resistance in Gc and host colonization in a murine model of gonorrhea, suggesting that lactate utilization contributes to virulence. Gc encodes four lactate dehydrogenases (LDHs) with distinct regulation and mechanisms, including two L-LDHs, LldD and LutACB. Although either enzyme alone supports L-lactate utilization, we found that both are required for full fitness during co-colonization with PMNs, indicating some non-redundant roles. Furthermore, LldD enhances oxidative stress resistance and is required for Gc colonization in a murine model of gonorrhea, whereas LutACB is dispensable. These findings identify LldD as a key factor promoting oxidative stress resistance, survival during PMN challenge, and host colonization.

Group B Streptococcus (Streptococcus agalactiae, GBS) is a leading cause of invasive infections in neonates and adults. The adult gastrointestinal (GI) tract represents an understudied site of asymptomatic carriage with potential relevance for both transmission and disease. Here, we establish a murine model of GBS colonization in the adult GI tract, which provides a tractable system for probing host-microbe interactions within this niche. Using this model, we establish that GI carriage is generalizable to diverse GBS isolates and leverage transposon sequencing (Tn-Seq) to identify candidate GBS factors important for GI colonization. Informed by these Tn-Seq data, we identify GBS capsule as a critical colonization factor of the adult murine GI tract. Taken together, this work highlights the GI tract as a reservoir for GBS and introduces a new experimental framework for investigating the bacterial and host determinants of GBS GI carriage.

Staphylococcus aureus is a leading cause of prosthetic joint infection (PJI) typified by biofilm formation. Anti-inflammatory granulocytic myeloid-derived suppressor cells (G-MDSCs) represent the main leukocyte population in a mouse model of S. aureus PJI, followed by neutrophils (PMNs), and macrophages (Mφs), which is also seen during human PJI. Defining how each leukocyte population responds to S. aureus biofilm vs planktonic bacteria could have important implications for how S. aureus evades immune detection to facilitate biofilm persistence. This study compared the kinetics of leukocyte death and relationship to mitochondrial ROS (mtROS) production following exposure to planktonic S. aureus or biofilm. Mφs were exquisitely sensitive to S. aureus biofilm with toxicity observed within 15 min following biofilm co-culture, whereas G-MDSCs and PMNs were more resilient, with appreciable survival out to 6 h. In contrast, G-MDSC viability was significantly decreased after extended exposure to planktonic S. aureus compared to PMNs and Mφs. Although leukocyte death coincided with increased mtROS production across all leukocyte populations, inhibiting mtROS had no impact on leukocyte survival following biofilm co-culture, suggesting alternative cell death triggers. Caspase-1-dependent pyroptosis was observed in PMNs, whereas Mφs and G-MDSCs were targeted by necrosis since an inhibitor of H₂O₂-induced necrosis improved cell survival of both populations, whereas programmed cell death inhibitors had no effect. These findings may account, in part, for the abundance of G-MDSCs and PMNs, but not Mφs, during PJI based on differential susceptibility to biofilm-induced cytotoxicity.

Klebsiella pneumoniae bacteremia is a significant public health burden with a 26% mortality rate, which increases when the infecting isolate is multidrug resistant. An important virulence factor of K. pneumoniae is its capsule, the protective polysaccharide coat that surrounds the outer membrane and is made up of individual capsular polysaccharide (CPS) chains. The capsule can differ in composition, abundance, surface attachment, and length of the individual CPS chains. Long, uniform CPS chains are associated with a high level of mucoidy. Typically, mucoidy is produced by the hypervirulent K. pneumoniae (hvKp) pathotype, which is associated with invasive community-acquired infections. In contrast, the classical K. pneumoniae (cKp) pathotype tends to be less mucoid or non-mucoid and is associated with nosocomial infections and multidrug resistance. There are over 80 serotypes of K. pneumoniae capsule. Capsule swap experiments have begun to reveal the effect of serotype on virulence and immune interactions. Clinically, the K2 capsule serotype is a common serotype associated with neonatal bloodstream infections. Both cKp and hvKp can produce K2 capsule, but how K2-encoding cKp and hvKp strains differ in a bloodstream infection remains unknown. To fill this gap in knowledge, we characterized the surface properties of K2 serotype cKp and hvKp bloodstream infection isolates then tested the fitness of these strains in bloodstream infection-related in vitro and in vivo assays. Understanding how K2 cKp and hvKp strains differ in pathogenic potential provides further insights into how K. pneumoniae capsule properties influence bloodstream infection pathogenesis.

Non-receptor tyrosine kinase c-Abl is critical for host defense against bacterial and viral infections, yet its role in antifungal immunity remains elusive. Here, we report that inhibition of c-Abl with flumatinib mesylate significantly impairs the survival rate and exacerbates fungal burden in mice infected with Candida albicans. Our findings reveal that c-Abl inhibition reduces production of TNF-α, IL-10, and IL-12 in bone marrow-derived dendritic cells (BMDCs) after stimulation with fungal β-glucan or α-mannan. Mechanistically, c-Abl inhibition significantly blocks p38 and extracellular signal-regulated kinases 1/2 (ERK1/2) activation in BMDCs after α-mannan stimulation in a c-Cbl dependent manner. Collectively, our study uncovers a c-Abl/c-Cbl/MAPK signaling axis in dendritic cells that governs antifungal innate immunity, highlighting c-Cbl as a critical downstream mediator linking c-Abl to host defense against C. albicans. Our findings provide a mechanistic basis for fungal risk assessment in cancer patients treated with c-Abl inhibitors.

Key bacterial vaginosis (BV)-associated bacteria implicated in biofilm formation include Gardnerella species, Prevotella bivia, and Fannyhessea vaginae. We investigated their spatial organization in the BV biofilm over time from longitudinal vaginal specimens obtained from women with incident BV (iBV) using peptide nucleic acid-fluorescence in situ hybridization (PNA-FISH). Heterosexual women with optimal vaginal microbiota self-collected vaginal specimens twice daily for 60 days or until iBV development (Nugent score 7-10 on ≥4 consecutive specimens). Women who developed iBV were matched to healthy controls by age, race, and contraceptive method. Gardnerella spp., P. bivia, and F. vaginae were quantified using PNA-FISH 2 days pre-iBV, the day of iBV, and 2 days post-iBV across five optical layers (z, z + 2, z + 4, z + 6, and z + 8 μm). Total counts of all three bacterial species were significantly higher on the day of iBV compared to 2 days pre-iBV (P = 0.011) and remained elevated 2 days post-iBV. Across most layers and time points, pooled mean Gardnerella spp. counts were significantly higher than F. vaginae counts (P ≤ 0.022-0.0003). On the day of iBV and 2 days post-iBV, pooled mean counts of Gardnerella spp. and F. vaginae progressively increased across most biofilm layers (P ≤ 0.043-0.0012). Controls had significantly lower counts of Gardnerella spp. and F. vaginae. P. bivia had low counts in all specimens. During the critical time period surrounding iBV, Gardnerella spp. are abundant throughout the developing biofilm and facilitate F. vaginae incorporation at later time points and higher biofilm layers. Additional research, including other Prevotella spp., is needed.IMPORTANCEBacterial vaginosis (BV) is the most common vaginal infection in reproductive-age women worldwide with a global prevalence of 30%. Recurrence rates can be up to 60% within 1 year of treatment. While BV is characterized as a polymicrobial biofilm infection, the exact etiology remains unknown. The BV biofilm may persist after antibiotic treatment, possibly due to incomplete eradication by current antimicrobial therapies, contributing to recurrent infection. Data are limited in evaluating the spatial formation of the BV biofilm around the time of incident BV. Providing a better understanding of this critical time period in incident BV pathogenesis is necessary to inform the development of prevention methods aimed at inhibiting biofilm formation and improving long-term treatment outcomes.