Biology and Life Sciences

Abstract: Maternal–fetal immune tolerance requires controlled immune quiescence toward the semi‑allogeneic fetus while preserving host defense. However, a static immunosuppression model does not fully explain key clinical phenomena, including heterogeneous pregnancy outcomes, abrupt onset of preeclampsia, and transient postpartum autoimmune activation. We propose a bistable dynamical framework in which maternal–fetal immunity operates between two attractor states: a tolerance state and an inflammation state. State transitions are governed by an integrated inflammatory burden (I), representing cumulative effects of hypoxia, tissue damage, infection, and mechanical stress. A forward threshold (T_f) triggers transition to inflammation, whereas a lower reverse threshold (T_r) governs recovery, generating hysteresis and a postpartum vulnerability window. Within this framework, recurrent miscarriage reflects elevated baseline inflammatory burden, preeclampsia results from acute threshold crossing, preterm birth from sustained inflammatory drive, and postpartum autoimmunity from delayed reverse transition. A composite peripheral immune index (PI = (Treg% × IL‑10)/(IL‑6 × sCD25)) is proposed as a potential translational readout pending validation.

Abstract:

Background. Multidrug resistance (MDR) has become a major global health threat, leading to the emergence of difficult-to-treat bacterial “superbugs” among both Gram-positive and Gram-negative species. In hospital settings, biofilm (BF)-producing staphylococci further aggravates this problem by markedly increasing tolerance to conventional antibiotics, thereby promoting chronic and potentially life-threatening infections. In the present study, 1,12-bis-triphenyl phosphonium dodecane bromide nanovesicles (BPPB, 45 nm), previously reported as bacteriostatic, but never investigated for their effects on formation of staphylococcal BF, were evaluated as a potential novel agent contrasting its development. Methods. A total of 12 highly BF-producing isolates from our collection, comprising 6 Staphylococcus aureus and 6 S. epidermidis strains, were selected and tested against BPPB to determine minimum inhibitory concentrations (MICs). Subsequently, BF inhibition activity was evaluated at ½ MIC, MIC, and 2× MIC concentrations. Vancomycin (V), used as reference antibiotic, was tested under the same experimental conditions. Results. BPPB exhibited MIC values ranging from 0.25 to 1.00 µg/mL, which were 1–4-fold lower than those of V. While V significantly inhibited BF formation only at concentrations 2 × MIC, and mainly against Bam and Aam isolates (96–97% inhibition), BPPB demonstrated potent and consistent inhibition activity against all strains, irrespective of species or resistance profile, determined by VITEK. BF inhibition values of 83–99%, 95–>99%, and 98–>99% were observed at ½ MIC, MIC, and 2 × MIC, respectively. Conclusions. Overall, the findings highlight both the strong BF-forming capability and MDR phenotype of the selected staphylococcal isolates, as well as the remarkable antibacterial and BF inhibition efficacy of BPPB nanovesicles, further confirming the superiority of nanomaterials (NMs) in exert biological effects. Importantly, the low cytotoxicity previously observed against eukaryotic Cos-7 and HepG2 cells resulting in high selectivity index (SI) values (23.0–90.5), supports BPPB as a promising candidate for the development of new NMs-based therapeutic strategies against MDR staphylococcal BF-associated infections.

Abstract: Background: Acinetobacter baumannii is a critical priority pathogen characterized by extensive multidrug resistance, leading to increased reliance on last-line polymyxins and widespread use of cationic disinfectants in healthcare settings. However, shared membrane-targeting mechanisms raise concerns regarding potential cross-resistance between disinfectants, polymyxins, and cationic antimicrobial peptides. Methods: A diverse panel of clinical A. baumannii isolates from Australia, Pakistan, and Switzerland, including polymyxin-resistant strains, was used to evaluate their antimicrobial resistance profiles. Minimum inhibitory concentrations (MICs) of polymyxin B, colistin, three cationic disinfectants (polyquaternium-1; PQ-1), polyhexamethylene biguanide (PHMB), and chlorhexidine (CHX)), and four AMPs (LL-37, melimine, Mel4, and lactoferricin) were determined using broth microdilution. Correlations between MICs were assessed using Spearman analysis, and differences between polymyxin-resistant and susceptible isolates were analysed statistically. Results: Most isolates were susceptible to polymyxins, although selected strains (12.9%) displayed high-level resistance. PQ-1 exhibited the greatest antibacterial activity among disinfectants, while LL-37 showed the lowest and most consistent MICs among AMPs; lactoferricin was largely inactive. Polymyxin-resistant isolates demonstrated significantly lower MICs to PQ-1 and PHMB, indicating collateral susceptibility. Correlation analysis revealed significant negative correlations between polymyxin susceptibility and disinfectant MICs (r=-0.48 to -11 and p= 0.005), whereas no consistent correlation was observed between polymyxins and AMPs, including LL-37. A moderate positive correlation was identified between colistin and Mel4 activity (r =0.45 and p =0.05). Conclusions: These findings demonstrate divergent susceptibility patterns of A. baumannii to cationic antimicrobials. Resistance to polymyxins was not associated with resistance to disinfectants or most AMPs and instead was linked to increased susceptibility to certain disinfectants. Importantly, the absence of cross-resistance with LL-37 suggests that host defense peptides and AMP-based therapeutics may remain effective against polymyxin-resistant strains. This study highlights the complexity of membrane-targeting antimicrobial resistance and underscores the need for further mechanistic investigations into cross-resistance and collateral susceptibility.

Abstract: Chronic obstructive pulmonary disease (COPD) is characterized by systemic inflammation, immune dysregulation, and increased susceptibility to infections. Obesity may influence these processes and has been proposed as a potential contributor to the so-called “obesity paradox”, although its effects on immune competence, viral burden, and survival are not yet fully understood. Seventy patients with severe to very severe COPD (GOLD stage 3–4) were stratified according to BMI (<30 vs. ≥30 kg/m²). Clinical and functional parameters were assessed together with biomarkers of oxidative stress, DNA damage, systemic inflammation, and T-cell subsets. A comprehensive viral panel, including Torque Teno virus (TTV), was also analyzed. Five-year survival was evaluated using Kaplan–Meier curves and Cox regression models. Patients with BMI ≥30 showed higher lymphocyte counts and increased CD4⁺ and CD8⁺ T-cell levels, accompanied by lower systemic inflammatory indices. No significant differences were observed in oxidative stress or DNA damage markers. In addition, TTV viremia (>4 log₁₀ copies/mL) was more frequently observed among patients with lower BMI. Despite these differences, five-year survival did not significantly differ between the two groups. These findings suggest that BMI alone may have limited value as a predictor of outcomes in patients with advanced COPD. Conversely, immune-inflammatory indices and viral burden, particularly TTV viremia, could provide complementary information for risk assessment and may deserve further investigation as potential tools for personalized patient stratification.

Abstract: Tumor progression emerges from a dynamic interaction between malignant cells and the immune system. The classical cancer immunoediting framework (elimination–equilibrium–escape) does not explicitly address three aspects: the foundational role of innate immunity in early surveillance, the dynamic evolution of immune tolerance, and the temporal heterogeneity of immune escape. Here, we propose a conceptual systems-immunology model in which tumor evolution is governed by two kinetic inequalities: (i) during progression, the effective neoantigen generation rate (r_Ag^eff) exceeds immune clearance capacity (r_clear); (ii) during escape, the tumor mutation rate (r_mut) exceeds the rate of effective immune response establishment (r_resp). We further hypothesize that chronic tumor evolution is shaped by a dynamic balance between T cell progenitor exhaustion (Tpex) accumulation and the strengthening of suppressive immune networks. Based on this framework, we propose a five-phase tumor–immune game model: baseline immune surveillance, acute immune clearance, immune tolerance, immune clearance transition, and immune escape. Transition from tolerance to clearance is modeled as a condition in which d(Tpex)/dt exceeds the growth rate of suppressive network potency for a sufficient duration (τ). If this condition is not met due to insufficient host survival time or dominant tumor growth/mutation dynamics, the system transitions directly into immune escape. This framework provides a phase-matched interpretation of immunotherapy and suggests two therapeutic axes: reducing antigenic evolution and enhancing immune recognition and clearance. All parameters are theoretical constructs and are not intended for clinical application.

Abstract: Mucosal surfaces constitute the principal immunological interface between mammals and their environments, continuously integrating dietary antigens, the commensal microbiota, and exposure to pathogens. These barrier sites are organized into compartmentalized immune networks that coordinate epithelial surveillance, antigen sampling, immunoglobulin A (IgA) diversification, and tissue-resident immune responses. However, prevailing paradigms in mucosal immunology are derived predominantly from murine and human systems and often assume broad conservation of mucosal immune organization across mammals. Emerging comparative evidence challenges this assumption as ruminants, monogastrics, carnivores, and reservoir wildlife species exhibit substantial divergence in mucosal architecture, Peyer’s patch ontogeny, epithelial sensing pathways, and immune–microbiota interactions, reflecting adaptation to distinct ecological and dietary pressures We propose that mucosal immunity serves as an ecological filter shaping microbial persistence, pathogen shedding, and zoonotic transmission at barrier sites where pathogen emergence initiates. Failure to account for species-specific mucosal immune organization may limit cross-species extrapolation of vaccine responses, microbiome-targeted therapeutics, and zoonotic risk prediction. We further argue that variation in mucosal compartmentalization contributes directly to reservoir competence by influencing immune tolerance, microbial filtering, IgA repertoire diversification, and pathogen persistence within host populations. Finally, we identify major unresolved questions and highlight the need for comparative spatial immunology and integrated mucosal multi-omics to develop predictive models of host–pathogen interaction within a One Health framework.

Abstract: Autoimmune diseases (AIDs) are characterized by recurrent flare–remission cycles, yet a unifying explanation for these dynamics remains lacking. Here, we propose a conceptual framework in which peripheral tolerance is maintained through dynamic interactions between regulatory T cells (Treg) and stem‑like autoreactive T cells (here termed Tpex‑like cells). In this model, clinical flares arise as dual‑threshold phase transitions, occurring when regulatory stability falls below a critical threshold and immune effector activity exceeds local tissue repair capacity. The framework integrates several common but incompletely connected observations across autoimmune diseases, including age‑dependent disease onset, benign autoantibody positivity, seronegative phenotypes, and fluctuating disease activity. We further propose that long‑term persistence of autoreactive immune reservoirs may contribute to disease susceptibility and recurrence, while age‑related immune remodeling may influence the timing of transition to clinically overt disease. By linking immune regulation, tissue resilience, and autoreactive cell dynamics within a unified conceptual model, the framework provides a potential explanation for heterogeneous clinical trajectories across pediatric‑, adult‑, and late‑onset autoimmune diseases. Importantly, all mechanistic interpretations and therapeutic implications remain theoretical and require experimental validation. The model generates testable predictions regarding autoreactive T‑cell dynamics, immune oscillations, and determinants of disease susceptibility and relapse.

Abstract: Background: Trimeric envelope-proximal domains in viral class I fusion proteins are conserved targets of broadly neutralizing antibodies (bNAbs), but it has proven difficult to develop vaccines against those targets. The HIV-1 gp41 membrane-proximal external region (MPER) is one such target. Induction of a neutralizing response likely depends on the immunogen having a close-to-native structure. Methods: Native sequence MPER was displayed on genome-reduced bacteria as a coiled-coil homotrimer using a Haemophilus influenzae Hia trimeric autotransporter. Vaccine designs incorporated additional features, including trimerization domains to stabilize MPER, tandem MPER repeats to increase antigen valency, and immunomodulatory elements. Antigen exposure was assessed by flow cytometry, antibody responses were evaluated by ELISA, and functional activity was measured using HIV-1 pseudovirus neutralization assays. Results: Trimer stabilization improved MPER exposure, but immunogen visibility alone did not predict neutralization. After three immunizations, neutralizing activity was detected only in the most extensively engineered vaccine, which neutralized tier 2 virus CNE55. After five immunizations, the same vaccine also neutralized the tier 2 virus 25710-2.43. A further design modification that included an extended Hia-derived spacer increased MPER exposure and antibody binding, with neutralization detected against MN.3, X1632_S2_B10, and 25710-2.43 viruses in subsets of animals. Conclusions: Native-sequence MPER can induce detectable, virus-dependent HIV-1 neutralizing activity when displayed in a carefully controlled trimeric bacterial surface-display platform. The results show that MPER vaccine performance depends not only on antigen exposure, but also on multimeric organization, immunomodulatory context, and antigen-scaffold geometry. Analogous coiled-coil trimeric bacterial surface display immunogens may inform vaccine development for stem/stalk regions of other Class I fusion protein viruses.

Abstract: HBV infection exhibits striking age-dependent outcomes: perinatal infection progresses to chronicity in ~90% of cases, whereas >95% of immunocompetent adults spontaneously clear infection. Conventional explanations invoking immune immaturity or tolerance fail to account for prolonged disease courses, intermittent ALT flares, heterogeneous antigen trajectories, or delayed functional cure. We synthesize emerging evidence from developmental immunology, T-cell exhaustion biology, and longitudinal clinical observations into an integrated conceptual framework for understanding age-dependent HBV outcomes. Longitudinal clinical observations—including non‑monotonic HBsAg decline, dynamic sIL‑2R fluctuations, and intermittent biochemical activity—suggest that chronic HBV immunity remains dynamically active rather than statically quiescent. The framework proposes that early regulatory dominance favors viral persistence, whereas gradual Tpex enrichment and functional reorganization intermittently shift immune balance toward effector activation. Recurrent cycles of partial activation, contraction, and replenishment may contribute to long‑term antigen reduction, phase transitions, and occasional functional cure. HBV's limited immune evasion allows host developmental immune states to dominate, explaining its uniquely strong age dependence compared with other hepatotropic or chronic pathogens. Rather than viewing chronic HBV infection as a static state of immune tolerance, this framework conceptualizes HBV persistence as a slowly evolving immunodynamic process characterized by recurrent regulatory–effector rebalancing. The model generates experimentally testable predictions and provides a conceptual foundation for future longitudinal and systems‑immunology studies.

Abstract: Salmonella is a globally significant foodborne intracellular pathogen, and invasive salmonellosis poses a major global public health threat. The NLR family CARD domain-containing protein 4 (NLRC4) inflammasome, a pivotal cytosolic innate immune sensor, specifically recognizes Salmonella flagellin and type III secretion system (T3SS) components via the NAIP (NLR family apoptosis inhibitory protein) family. Upon activation, it triggers pyroptosis, pro-inflammatory cytokine release, and infected intestinal epithelial cell extrusion, serving as a central pathway for host defense against Salmonella colonization and systemic spread. In this review, we systematically summarize the structural composition, activation mechanisms, post-translational modifications, and regulatory protein network of the NLRC4 inflammasome. This review highlights the molecular mechanisms by which Salmonella evades NLRC4 surveillance through multiple strategies: transcriptional downregulation of immunogenic ligands, structural modification of T3SS components, secretion of effector proteins, and chemotaxis-virulence synergy. This review comprehensively presents the co-evolutionary arms race between Salmonella and the NLRC4 inflammasome, providing a theoretical basis for elucidating bacterial immune evasion mechanisms and developing novel anti-infective targets.

Abstract: Immune checkpoint inhibitors (ICIs) are now being introduced into perioperative treatment for several solid tumors. This strategy is usually explained by tumor reduction before surgery or by the elimination of minimal residual disease (MRD) after surgery. However, these explanations may not be sufficient to understand why the timing of ICI treatment, especially before lymph node (LN) removal, is important. In this review, we discuss tumor-draining lymph nodes (tdLNs) from two different aspects. tdLNs are anatomical routes for regional and distant metastasis, but they are also sites where tumor antigens are presented and tumor-specific T cell responses are generated. In particular, tdLNs may maintain stem-like or progenitor-exhausted CD8⁺ T cells, which can respond to PD-1 blockade and give rise to more differentiated exhausted T cells in the tumor. From this viewpoint, neoadjuvant ICI may be effective because the primary tumor, antigen flow, dendritic cell migration, and tdLN-based T cell priming are preserved. We also discuss the possible role of adjuvant ICI in controlling MRD, micrometastases, and metastatic-site draining LNs, and consider future implications for LN surgery and postoperative immune surveillance.

Abstract: Polyamines such as putrescine, spermidine, and spermine are small, positively charged organic cations that interact with negatively charged molecules, notably nucleic acids. These molecules play a vital role in cell proliferation, differentiation, and growth. Their involvement in wound healing has attracted considerable research interest, as they are key regulators of keratinocyte and fibroblast proliferation—two cell types essential for re-epithelialization and tissue regeneration. Polyamines also influence gene expression and protein synthesis, facilitating the transition of cells from a quiescent to an active state during the healing process. Enzymes such as Adenosylmethionine Decarboxylase 1 (AMD1), which are involved in polyamine biosynthesis, are upregulated during wound healing and contribute to gene regulation at multiple levels. In parasitic protozoa—including Plasmodium falciparum (malaria), Trypanosoma spp. (sleeping sickness), and Leishmania spp. (leishmaniasis)—polyamines are crucial for DNA stabilization, protein synthesis, and cellular proliferation. These parasites depend on both endogenous polyamine synthesis and host-derived polyamines to sustain their metabolic functions. Notably, Plasmodium falciparum, the causative agent of malaria, possesses a bifunctional enzyme complex linking S-Adenosylmethionine decarboxylase (AdoMetDC) and ornithine decarboxylase (ODC), unlike the human form, where these enzymes are separate. This structural distinction makes the parasite’s AdoMetDC/ODC complex a promising target for drug development. In Mycobacterium tuberculosis (Mtb), polyamine metabolites have been shown to influence DNA methylation patterns, thereby affecting gene expression and bacterial adaptation. A 2025 study revealed that altered polyamine levels in the blood of patients with multidrug-resistant TB were associated with changes in Mtb DNA methylation, suggesting a potential role in resistance mechanisms. This chapter explores the multifaceted roles of polyamines in wound healing, parasitic infections, and tuberculosis-related bacteria. It also considers emerging technologies for wound treatment and highlights parasite-specific targets that may inform novel therapeutic strategies against TB.

Abstract: With further research on the relationship between gut microbiota and human health, discussions on various gut-X axis have been increasingly prevalent. Evidence indicates that microbiota dysbiosis is closely linked to the onset and progression of audiovestibular disorders and the gut-ear axis has gradually been recognized as a vital systemic regulatory pathway. This article systematically reviewed the interaction mechanisms between microbiota dysbiosis and audiovestibular diseases, intervention strategies, research limitations and future perspectives. This axis functions mainly through immune-mediated barrier damage, metabolic disorder and neurotransmitter crosstalk. Modulation of the gut microbiota can alleviate symptoms of certain audiovestibular disorders. This review aims to provide novel insights for the pathogenesis, intervention and clinical management of audiovestibular disorders.

Abstract: Background: Despite circulation of evolutionarily related cold-causing coronaviruses (CCCs) in the pre-COVID era, most individuals lacked pre-existing serum IgG and/or class-switched memory B cell (B_mem) reactivity for the SARS-CoV-2 Spike (S) glycoprotein expressed by the ancestral Wuhan-Hu-1 (WH1) strain. Subsequent priming of the immune system through natural infection or prophylactic COVID-19 mRNA vaccination successfully generated robust B_mem responses against the WH1-S antigen, along with eliciting cross-reactivity for the future Omicron (BA.1) variant responsible for breakthrough infections (BTIs). However, to what extent immunological imprinting of B_mem towards the WH1-S antigen detrimentally constrains elicitation of variant-specific antibody responses following subsequent booster vaccinations or BTIs—a phenomena referred to as “original antigenic sin”—remains an unresolved and open question. Methods: Using ImmunoSpot^® we evaluated peripheral blood mononuclear cells (PBMCs) from defined human cohorts for IgG⁺ ASC reactivity against Spike proteins representing CCCs and SARS-CoV-2. Additionally, we developed a novel dual-label inverted FluoroSpot assay to distinguish between strain-specific and cross-reactive IgG⁺ ASCs recognizing epitopes in the receptor binding domain (RBD) of SARS-CoV-2 Omicron variants. Results: Our data demonstrate a lack of appreciable back-boosting of IgG⁺ B_mem recognizing structurally conserved epitopes shared between CCCs and SARS-CoV-2. Moreover, we found evidence for immunological imprinting and preferential expansion of B_mem recognizing cross-reactive epitopes in the RBD following BTI. Nevertheless, Omicron strain-specific B_mem were detected in PBMC donors collected in 2025. Conclusions: Our novel inverted dual-label FluoroSpot methodology provides a highly flexible, easily implementable technique for distinguishing between strain-specific and cross-reactive B cell responses in translational vaccine research.

Abstract: Hantavirus pulmonary syndrome (HPS) is a severe disease first recognised in the United States in 1993, with a case fatality rate approaching 35–50%. Since the identification of Sin Nombre virus during the Four Corners outbreak, understanding the transmission dynamics and geographic distribution of hantaviruses has become critical for public health planning and prevention. This review synthesises evidence from ecological niche modelling, epidemiological surveillance, and environmental analyses to explain patterns of hantavirus occurrence in North America. The findings indicate that HPS risk is associated with dry climates, rural and peri-urban landscapes, rodent host ecology, and increased social vulnerability, with cases primarily concentrated in the western United States. We examine how environmental conditions, rodent ecology, human–rodent interactions, and socioeconomic factors interact to influence disease risk. This synthesis provides recommendations for reducing exposure in high-risk populations and regions.

Abstract: Cytokine storm syndromes arise from a systemic collapse of immune homeostasis due to dynamic imbalance between danger load (L) and immune buffer capacity (B). Existing linear “danger signal → inflammation” models cannot explain why high antigen loads sometimes produce only mild inflammation, why hyperinflammation and immunosuppression often co‑exist, or why similar danger signals lead to divergent clinical outcomes. Here we propose a systems immunology framework: L represents the total pro‑inflammatory pressure, while B is a network of promoting and suppressive forces analogous to acid–base or coagulation buffers. We introduce a dynamic S‑index (S_actual ≈ Treg/Teff functional ratio) as an “immunological pH” for the adaptive arm. Four equilibrium states are defined – high‑buffer, low‑buffer, promoting‑dominant, and suppressive‑dominant – each with distinct storm pathways (direct vs. indirect). Three dominant dynamic states are described: innate‑driven collapse (immune‑deficiency‑associated and massive necrosis types), adaptive dynamic mismatch (a four‑stage progression), and mixed oscillatory states. Differences between PAMP and DAMP are clarified, and diverse storm phenotypes are mapped onto a unified state space. The framework explains inter‑individual heterogeneity and temporal evolution, and it provides a rationale for individualized therapy. Several experimentally testable predictions are proposed. All quantitative descriptions are purely theoretical and await experimental validation.

Abstract: Metallo-β-lactamase (MBL)-producing multidrug-resistant (MDR) bacteria have emerged as one of the most critical threats to global public health. These zinc-dependent enzymes, particularly NDM, VIM, and IMP, hydrolyze carbapenems, the last-resort antibiotics for treating severe Gram-negative infections. Unlike serine-β-lactamases, MBLs evade all clinically approved β-lactamase inhibitors, leaving a profound therapeutic vacuum. This review synthesizes evidence from 204 peer-reviewed articles (1970–2026) to examine the molecular diversity, global burden, diagnostic approaches, risk factors, and future directions for MBL-producing pathogens, including Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii. MBL genes are predominantly disseminated via mobile genetic elements (plasmids and integrons) and high-risk clones, facilitating rapid cross-border spread. Geographic disparities are striking: Asia accounts for 80% of MBL-producing Acinetobacter reports, while the Eastern Mediterranean and Africa show the highest prevalence of carbapenem-resistant A. baumannii (42.1% and 36.1%, respectively). In contrast, Europe and the Americas report prevalence below 1%, though absolute case numbers remain substantial due to robust surveillance. Phenotypic detection methods (combined disc test, E-test, and modified Hodge test) are practical in resource-limited settings but suffer from poor specificity and subjective interpretation. Genotypic methods (PCR, whole-genome sequencing, and MALDI-TOF MS) offer definitive gene identification but require specialized infrastructure and expertise. Critical risk factors for MBL acquisition include prior carbapenem exposure, prolonged ICU stays, invasive devices, immunosuppression, and healthcare-associated transmission. The absence of Food and Drug Administration (FDA)-approved MBL inhibitors forces reliance on antibiotics that have limited efficacy, high toxicity, and emerging resistance. Addressing this crisis demands a coordinated, multi-pronged strategy: strengthening global genomic surveillance; deploying rapid molecular diagnostics at the point of care; accelerating the development of novel MBL inhibitors; enforcing antimicrobial stewardship to curb carbapenem overuse; and implementing rigorous infection prevention and control measures.

Abstract: Staphylococcus aureus is a Gram-positive bacterium responsible for a broad spectrum of human infections. Staphyloxanthin (STX), a golden carotenoid pigment synthesized by the crtOPQMN operon, contributes to S. aureus virulence by enhancing resistance to oxidative stress and promoting immune evasion. STX functions as an antioxidant by scavenging free radicals and neutralizing reactive oxygen species, thereby helping S. aureus withstand neutrophil-mediated killing. In murine infection models, STX-producing strains form larger abscesses than pigment-deficient mutants, supporting a role for pigment production in bacterial survival and pathogenicity. Accordingly, targeting STX biosynthesis has emerged as a promising anti-virulence strategy. Several natural and synthetic compounds have been reported to inhibit STX production, reducing pigment synthesis without directly inhibiting bacterial growth and rendering bacteria more vulnerable to immune clearance. This review summarizes the genetic basis, regulation, and virulence-associated functions of STX and discusses recent advances in anti-virulence strategies that target pigment biosynthesis. These approaches may provide new therapeutic avenues for weakening antibiotic-resistant S. aureus strains while reducing direct selective pressure for resistance compared with conventional bactericidal antibiotics.

Abstract: Gopher tortoises (Gopherus polyphemus) are an environmentally threatened keystone species, whose burrows provide food and shelter for over 300 animal species. As part of an intensive field study of 11 wild gopher tortoise populations in Florida, we obtained clinical isolates (N=12) from the nares of tortoises. Based on 16S rRNA sequencing, one isolate was identified as Acholeplasma hippikon but the other 11 isolates grouped together and were distinct from other known Acholeplasma spp. The clinical isolates (N=11) from tortoises from 7 different geographical sites in north central Florida were characterized phenotypically and by 16S rRNA, whole genome sequence, and proteome phylogenies as a new species. Based on the isolation source history, phenotypic, and phylogenetic characteristics, we propose the name Acholeplasma testudinis sp. nov.; strain ORD1043 was chosen as the Type strain. To determine potential pathogenicity, tortoises were inoculated intranasally with either 108 CFU of A. testudinis ORD1043Ts (N=9, Infected) or sterile SP4 broth (N=7, Control). Tortoises were followed throughout the study for occurrence of clinical signs, necropsied at 91 days post infection, and histological lesions in the upper respiratory tract determined. Despite the high infectious dose used, mean clinical sign scores were very low and mild overall, and histopathological lesions were not consistently observed in the infected group. We therefore concluded that A. testudinis is not a significant pathogen but is a likely commensal that can colonize the tortoise but does not cause significant disease or tissue damage to the host.

Abstract: Shiga toxins (Stx), produced by Stx-producing Escherichia coli (STEC), are known to target Gb3-expressing cells, contributing to organ pathology such as kidney and brain. However, the sensitivity of human B-lymphoblastoid cell lines to Stx2 and their Gb3 expression profiles remain poorly understood. In this preliminary study, we assessed the susceptibility of human B-lymphoblastoid cell lines to Stx2 and identified distinct resistance and sensitivity patterns. Eight representative lines were further analyzed for Gb3 expression by mass spectrometry and flow cytometry. Susceptible cell lines (e.g., GM02473, GM07019) displayed significantly higher total and membrane-associated Gb3 levels, while resistant lines had lower or undetectable Gb3. Exosomal Gb3 quantification revealed similar expression trends, contradicting the hypothesis that Gb3-positive exosomes neutralize Stx2. Interestingly, partially resistant cell line GM17658 showed discordant total and exosomal Gb3 levels. Immunofluorescence microscopy and flow cytometry revealed heterogeneous Gb3 expression within cell lines, with susceptible lines having a higher proportion of Gb3-positive cells. These findings suggest that Stx2 susceptibility is associated with Gb3 expression frequency rather than intensity and raise the possibility that Gb3-positive exosomes might contribute to toxicity. Future studies need to validate the role of exosomal Stx2 transfer and the functional impact of variable levels of Gb3-positive versus Gb3-negative subpopulations in toxin response.