Search Results (920)

Bacillus anthracis displays susceptibility to penicillin despite harboring a β-lactamase gene, a phenotype governed by the anti-sigma factor RsiP. While RsiP represses σ^P-dependent β-lactamase expression, its broader roles in physiology and virulence remain unclear. This study aimed to define the global regulatory functions of RsiP beyond antibiotic resistance. Deletion of rsiP significantly upregulated the nprR gene, which is an important quorum-sensing (QS) system regulator and enhanced protease secretion. The ΔrsiP mutant caused higher mortality in cellular and Galleria mellonella models and triggered elevated inflammatory cytokines (IL-6, IL-1β, TNF-α, MIP-2) in macrophages models. Surprisingly, in DBA/2 mice models, ΔrsiP was attenuated, with increased host survival and reduced bacterial loads. Competitive indices (CI) confirmed fitness defects in mice (spleen CI = 0.39; liver CI = 0.42). These defects were not due to altered oxidative stress tolerance but were attributed to impaired macrophage internalization of ΔrsiP spores, reducing early colonization. Our findings indicate that RsiP not only modulates β-lactam resistance but also influences extracellular protease activity and host adaptation. Full article

Bacterial pathogens exploit host-derived nutrients to coordinate metabolism and virulence determinants to optimize fitness in vivo. In Pseudomonas aeruginosa, GlnK is a central regulator of nitrogen metabolism. It senses the intracellular nitrogen status by integrating 2-oxoglutarate (2-OG) and glutamine signals, which in turn triggers its uridylylation and conformational changes. This reversible post-translational modification modulates its interaction with target proteins, thereby precisely regulating carbon-nitrogen metabolic homeostasis and enabling adaptive nitrogen metabolism in response to host-derived nutrient cues. In this study, we found that glnK is upregulated during infection in a mouse pneumonia model. By growing bacteria in mouse bronchoalveolar lavage fluid (BALF), we demonstrated that the expression of glnK is activated by the NtrB-NtrC two-component regulatory system in response to the host nutrient environment. Mutation of glnK impairs bacterial virulence. Transcriptomic analysis revealed downregulation of the type III secretion system (T3SS) genes in the glnK mutant. Further studies revealed a role of GlnK in maintaining the homeostasis of the NtrB-NtrC system through a negative feedback mechanism, which is required for the expression of the T3SS genes. Collectively, these findings reveal a role of GlnK in interconnecting carbon–nitrogen balance and the T3SS in response to the host environment. Full article

Neospora caninum, the causative agent of abortion in cattle, has a major economic impact worldwide. This review aims to provide an overview of key advances over the last 10 years in understanding host−pathogen interactions, molecular mechanisms, and emerging control strategies and puts them into a context with previously published important findings. More recently, novel diagnostic tools with improved sensitivity and specificity have been developed. These have supplemented the already existing methods to detect infection in clinical cases and are essential for investigations on parasite distribution, disease incidence and prevalence, and transmission of N. caninum. Epidemiological studies have revealed the influence of environmental, genetic, and ecological factors on parasite transmission dynamics, and emphasized the importance of integrated “One Health” strategies. Characteristics of different Neospora strains have been elucidated through animal models and molecular tools such as clustered regularly interspaced short palindromic repeats/CRISPR associated protein 9 (CRISPR/Cas9)-based gene editing, high-throughput sequencing, and advanced proteomics, aiming to shed light on stage-specific gene regulation and virulence factors, contributing to the development of interventions against neosporosis. Insights into immune modulation, immune evasion, and parasite persistence contributed to the efforts towards vaccine development. In terms of therapeutics, both repurposed drugs and more targeted inhibitors have shown promising efficacy in reducing parasite burden and mitigating vertical transmission in laboratory models. Here, more recent innovations in nanoparticle-based drug delivery systems and immunomodulatory strategies are prone to enhancing therapeutic outcomes. However, a significant challenge remains the integration of molecular and immunological insights into practical applications. Full article

Carbapenem-resistant Klebsiella pneumoniae (CRKP) has become a major cause of bloodstream infections and poses serious challenges to clinical management because treatment options are limited. This study aimed to characterize antimicrobial resistance, virulence-associated features, and molecular epidemiology of CRKP bloodstream isolates using integrated phenotypic and genomic approaches. A total of 74 non-duplicate CRKP isolates were collected from bloodstream infections at three tertiary-care hospitals in Riyadh, Saudi Arabia, between 2022 and 2024. All isolates showed classical Klebsiella pneumoniae phenotypic characteristics, including intrinsic resistance to natural and aminopenicillins, and were classified as either multidrug-resistant (MDR) or extensively drug-resistant (XDR). Resistance to imipenem was universal, and resistance to other β-lactams and fluoroquinolones was high. Carbapenemase genes were detected in 96.0% of isolates using the GeneXpert^® Carba-R assay, with bla_OXA-48-like and bla_NDM being most common. Whole-genome sequencing demonstrated predominance of Ambler class D carbapenemases, particularly bla_OXA-232, with additional contributions from bla_NDM-1 and bla_NDM-5. Co-occurrence of carbapenemase genes was observed in a subset of isolates. Virulence analysis showed that 37.8% of isolates exhibited a hypermucoviscous phenotype, and more than half carried at least one virulence-associated determinant linked to capsule regulation or iron acquisition. In contrast, most isolates showed weak or no biofilm-forming capacity. Multilocus sequence typing revealed substantial genetic diversity but clear dominance of high-risk lineages, particularly ST147 and the emerging ST2096, both closely associated with bla_OXA-232 and bla_OXA-48-like genes. Capsular and O-antigen analysis showed a non-random distribution dominated by KL64 and O1/O2. Phylogenetic analysis was consistent with clonal expansion and suggested intra-hospital spread, with the intensive care unit serving as a key reservoir and dissemination to other wards. In conclusion, CRKP bloodstream infections in this setting are largely associated with a limited number of epidemic clones that combine extensive antimicrobial resistance with virulence-associated traits. These findings support the need for ongoing genome-based surveillance, strengthened infection control measures, and antimicrobial stewardship to limit the spread of high-risk K. pneumoniae lineages in healthcare settings. Full article

Salmonella Typhimurium is a major zoonotic pathogen, with pigs and chickens serving as key reservoirs for human infection, yet the genomic determinants of its host adaptation remain incompletely understood. This study integrated comparative genomics, genome-wide association studies (GWASs), and interpretable machine learning on 1654 high-quality genomes of swine- and chicken-origin S. Typhimurium isolates to identify host-associated genetic features. Phylogenetic analysis revealed host-preferred lineages and significantly lower genetic diversity within chicken-adapted subpopulations. Meta-analysis identified distinct host-associated profiles of antimicrobial resistance genes (e.g., higher prevalence of floR and bla_TEM-1 in swine) and virulence factors (e.g., enrichment of allB and the yersiniabactin system in chickens). GWASs pinpointed 1878 host-associated genes and multiple SNPs/indels, functionally enriched in metabolism, regulation, and cell processes. A two-stage Random Forest model, built using the most contributory features, accurately discriminated between swine and chicken origins (AUC = 0.974). These findings systematically revealed the genomic signatures of host adaptation in S. Typhimurium, providing a prioritized set of candidate markers for experimental validation. Full article

For 12 isolates of Ilyonectria mors-panacis and 4 isolates of Ilyonectria robusta, the number of genes in the secretome showed a negative correlation with growth rates in culture, especially for small secreted non-cysteine-rich and cysteine-rich proteins, and several proteases and lipases, while it was positively correlated with genes for six CAZyme classes/modules and other proteases and lipases. However, this significant correlation with growth rate was influenced by the I. robusta isolates mostly having faster growth rates than the I. mors-panacis isolates on PDA, indicating a species-level difference. The only significant relationship of gene number to virulence was a positive correlation with genes for secreted glycoside hydrolases in families 18 and 78, and this was related to differences between isolates, even if only I. mors-panacis isolates were examined, indicating a difference within species. Glycoside hydrolase family 18 includes chitinase-like proteins, endo-β-N-acetylglucosaminidases, lectins, and xylanase inhibitors, which could help suppress triggered immunity by the host and regulate fungal xylanase activity. Glycoside hydrolase family 78 contain α-L-rhamnosidases that can cleave flavonoid glycosides, saponins, and ginsenosides, which could degrade antimicrobial compounds produced as a host response during infection. These results indicate that the number of certain classes of secreted enzymes could be a factor in both growth rate in culture and virulence. Full article

Helicobacter pylori is a prevalent gastric pathogen that establishes chronic infection and contributes to gastritis, peptic ulcer disease, and gastric cancer. Its persistence depends on immune evasion strategies that promote sustained low-grade inflammation in the gastric mucosa. Nucleotide-binding oligomerization domain-like receptors (NLRs) are cytosolic pattern recognition receptors that play key roles in innate immune responses against H. pylori. Nod1 and Nod2 detect bacterial peptidoglycan delivered via the type IV secretion system or outer membrane vesicles, activating NF-κB, MAPK, and interferon signaling pathways that regulate inflammatory cytokine production, epithelial barrier function, autophagy, and antimicrobial defense. The NLRP3 inflammasome mediates the maturation of IL-1β and IL-18 primarily in myeloid cells, thereby shaping inflammatory and immunoregulatory responses during infection. In contrast, NLRC4 functions in a context-dependent manner in epithelial cells and is largely dispensable for myeloid IL-1β production. Emerging evidence also implicates noncanonical NLRs, including NLRP6, NLRP9, NLRP12, NLRX1, and NLRC5, in regulating inflammation, epithelial homeostasis, and gastric tumorigenesis. In addition, genetic polymorphisms in NLR genes influence host susceptibility to H. pylori-associated diseases. This review highlights the interplay between NLR signaling, bacterial virulence, and host immunity and identifies potential therapeutic targets. Full article

The aim of the study was to investigate the early response of apple fruit infected with Penicillium expansum (P. expansum) to blue light-emitting diode (LED) light (BLL) irradiation. To focus our study on the interaction between apple fruit, the pathogen, and BLL, the effect of BLL was also studied on apples without P. expansum and P. expansum grown on malt extract agar (MEA). Transcriptome analysis revealed that the most pronounced responses among biological processes were observed in inoculated apples under BLL. The upregulated processes included water transport, response to heat, and response to high light intensity. The defence response of apples was enhanced by the upregulation of thaumatin-like proteins and caffeic acid 3-O-methyltransferase, while the cellular response to phosphate deficiency and the regulation of multicellular organism development were downregulated. In P. expansum grown on apples under BLL, transcriptome analysis revealed downregulation of genes related to signalling, response to organic compounds, and regulation of metabolic and biosynthetic processes, while genes involved in the biosynthesis of secondary metabolites were upregulated. In addition, the expression of patulin cluster genes was predominantly downregulated in P. expansum. The significant upregulation of genes related to cryptochrome inhibition, defence response, and caffeic acid metabolism in apples under BLL, together with the reduced virulence of P. expansum, contributes to the inhibition of fungal growth. Full article

Zinc (Zn), a ubiquitous environmental transition metal primarily existing as Zinc ions (Zn²⁺), plays a critical role in various biological processes. Its extensive application in agriculture, industry, and healthcare has led to significant environmental contamination. However, the mechanistic contribution of Zn²⁺ to bacterial antibiotic resistance and virulence remains insufficiently understood. This review explores the sources, cycling, and environmental accumulation of Zn²⁺ in a One Health context, emphasizing their impact on bacterial antibiotic resistance and virulence. Zn²⁺ promote bacterial antibiotic resistance by regulating efflux pumps, biofilm formation, expression and transfer of antibiotic resistance genes, as well as synergistic effects with other heavy metals and antibiotics. Meanwhile, Zn²⁺ promote bacterial virulence by regulating quorum sensing, secretion and metal homeostasis systems, as well as oxidative stress response and virulence factor expression. Additionally, it highlights the potential of targeting Zn homeostasis as a strategy to combat environmental antibiotic resistance. Collectively, these findings provide key insights into the mechanisms by which Zn²⁺ regulate bacterial antibiotic resistance and pathogenicity, offering valuable guidance for developing strategies to mitigate the global threat of antibiotic resistance. Full article

Maize (Zea mays L.) is a major economic crop highly susceptible to Colletotrichum graminicola, the causal agent of anthracnose leaf blight, which causes substantial annual yield losses. This fungal pathogen employs numerous effectors to manipulate plant immunity, yet the functions of many secreted proteins during biphasic infection remain poorly characterized. In this study, we identified CgMas2, a candidate secreted protein in C. graminicola and a homolog of Magnaporthe oryzae MoMas2. Deletion of CgMAS2 in the wild-type strain CgM2 did not affect fungal vegetative growth or conidial morphology but significantly impaired virulence on maize leaves. Leaf sheath infection assays revealed that CgMas2 is required for biotrophic invasive hyphal growth, as the mutant showed defective spreading of invasive hyphae to adjacent cells. Subcellular localization analysis indicated that CgMas2 localizes to the cytoplasm of conidia and to the primary infection hyphae. Furthermore, DAB staining demonstrated that disrupt of CgMAS2 leads to host reactive oxygen species (ROS) accumulation. Comparative transcriptome analysis of maize infected with ΔCgmas2 versus CgM2 revealed enrichment of GO terms related to peroxisome and defense response, along with up-regulation of benzoxazinoid biosynthesis genes (benzoxazinone biosynthesis 3, 4 and 5) at 60 h post-inoculation (hpi). Conversely, six ethylene-responsive transcription factors (ERF2, ERF3, ERF56, ERF112, ERF115 and ERF118) involved in ethylene signaling pathways were down-regulated at 96 hpi. These expression patterns were validated by RT-qPCR. Collectively, our results demonstrate that CgMas2 not only promotes invasive hyphal growth during the biotrophic stage but may also modulate phytohormone signaling and defense compound biosynthesis during the necrotrophic phase of infection. Full article

RNA methyltransferases are key regulators of bacterial physiology, yet their specific roles in virulence remain poorly defined. In this study, we characterize PA3840, a putative RNA methyltransferase in Pseudomonas aeruginosa (P. aeruginosa). Deletion of PA3840 specifically impaired twitching motility without affecting bacterial growth, swimming, or swarming. Notably, PA3840 was found to suppress the expression of Type III Secretion System (T3SS) genes, thereby reducing cytotoxicity and host cell rounding. Consistent with these observations, PA3840 expression attenuated pro-inflammatory cytokine production in epithelial cells by inhibiting NF-κB activation. Mechanistic analysis revealed that PA3840 is translocated into host cells in a Type VI Secretion System (T6SS)-dependent manner. This translocation was reduced by hcp1 deletion and nearly abolished by a double deletion of pscF and hcp3, suggesting the involvement of multiple T6SS components and potential interplay with T3SS machinery. However, direct transfection of PA3840 into host cells failed to suppress cytokine expression, indicating that its immunomodulatory function is mediated by a bacterium-intrinsic mechanism rather than direct intracellular action. Collectively, these findings identify PA3840 as a translocated effector that modulates twitching motility and dampens host inflammation by repressing T3SS and NF-κB signaling, revealing a novel layer of post-transcriptional virulence regulation in P. aeruginosa. Full article

Antimicrobial resistance (AMR) is escalating worldwide, posing a serious threat to global public health by driving infections that are no longer treatable with conventional antibiotics. CRISPR–Cas technology offers a programmable and highly specific therapeutic alternative by directly targeting the genetic determinants responsible for resistance. Various CRISPR systems can restore antibiotic susceptibility and induce selective bactericidal effects by eliminating resistance genes, disrupting biofilm formation, and inhibiting virulence pathways. Moreover, CRISPR can suppress horizontal gene transfer (HGT) by removing mobile genetic elements such as plasmids, thereby limiting the ecological spread of AMR across humans, animals, and the environment. Advances in delivery platforms—including conjugative plasmids, phagemids, and nanoparticle-based carriers—are expanding the translational potential of CRISPR-based antimicrobial strategies. Concurrent progress in Cas protein engineering, spatiotemporal activity regulation, and AI-driven optimization is expected to overcome current technical barriers. Collectively, these developments position CRISPR-based antimicrobials as next-generation precision therapeutics capable of treating refractory bacterial infections while simultaneously suppressing the dissemination of antibiotic resistance. Full article

The greater amberjack (Seriola dumerili) is an economically important marine species that is prone to bacterial infections, resulting in high mortality rates and substantial economic losses. In this study, a virulent bacterial strain, Vh-2, was isolated from diseased greater amberjack and identified as Vibrio harveyi. Experimental infections caused high mortality and severe splenic damage characterized by tissue necrosis, abnormal pigment deposition, cellular disintegration, and extensive immune cell infiltration. A virulence gene analysis revealed that Vh-2 harbored multiple virulence-associated genes such as toxR, toxS, vhpA, vhpB, vhhA, vhhB, luxR, and pap6. Antibiotic susceptibility testing demonstrated ampicillin resistance but sensitivity to ceftriaxone, florfenicol, and meropenem. Transcriptomic profiling of infected spleens identified 396 differentially expressed genes (DEGs) compared to the control group, of which 293 were upregulated and 103 were downregulated. A functional enrichment analysis indicated that these genes were primarily involved in cell cycle regulation, DNA repair, metabolic processes, and immune-related pathways. These findings enhance our understanding of V. harveyi pathogenesis and immune responses of S. dumerili and provide new insights into the prevention and control of V. harveyi infections in marine fish. Full article

Cryptococcus neoformans is a pathogenic yeast and the leading cause of cryptococcosis in humans. The calcium-calcineurin signaling pathway plays a central role in stress adaptation and virulence. To identify the uncharacterized regulators of fungal adaptation, we utilized an integrative systems biology approach, combining differential gene expression and network analysis using transcriptomic data from three key components of the calcium-calcineurin pathway (Cna1, Crz1, and Pmc1). Our workflow identified the CNAG_00522 gene product, which we designated tricalbin 1 (TCB1) due to its conserved calcium and lipid-binding C2 domains. TCB1 expression was found to be regulated by both Cna1 and Pmc1. Network analyses positioned Tcb1 as a bottleneck linking general stress response and cellular processes. Further molecular characterization confirmed that TCB1 expression is temperature and calcium-responsive. Functional studies of the tcb1Δ mutant revealed an enlarged capsule, increased GXM shedding, and enhanced viability under host-mimicking conditions. However, phenotypic screening demonstrated that the tcb1Δ mutant does not display sensitivity to cell wall or osmotic stressors, and TCB1 deletion did not attenuate virulence in the Tenebrio larval model. These findings suggest that TCB1 functions as a specialized regulator of fungal growth at 37 °C, capsule size, and GXM shedding. This study validates our integrative approach for guiding the identification of these complex regulators. Full article

Protozoa use iron to grow, feed, and cause harm through elaborate mechanisms to obtain it from the host. In addition, expression of virulence genes is affected by iron. In Entamoeba histolytica, the parasite that causes amoebic dysentery and complications in human organs, our group have previously reported the presence of an IRE/IRP-like (Iron Responsive Element/Iron Regulatory Protein) mechanism. Giardia duodenalis is another parasite of medical interest that causes giardiasis, including nutrient malabsorption syndrome and dysbiosis, among other complications, such as anemia in children with giardiasis. Moreover, expression of many putative giardial virulence factors by free-iron levels has been reported. Recently, we have reported stem-loop structures in some mRNAs coding virulence proteins from both parasites. However, much remains to be studied about the role of iron in pathogenesis. In this review, we summarize several aspects of gene expression regulation by iron in these protozoa as well as an iron regulatory mechanism in E. histolytica and discuss the possibility of an iron regulatory IRE/IRP-like mechanism in G. duodenalis. Full article