Streptococcus suis is a pathogenic bacterium primarily found in pigs, where it causes sudden death and meningitis, but it is also capable of causing septic shock and meningitis in humans, being the most important cause of adult bacterial meningitis in Southeast Asia. As the host's innate immune system serves as the first line of defense against microbial invaders, it is crucial to understand the intricate relationship between the bacterium and this system. Despite an increasing number of studies performed in the last 20 years, the pathogenesis of S. suis infection is not fully understood, and there is still an absence of effective vaccines on the market. Recent population-genomic studies have further highlighted that pathogenic S. suis is not a single uniform entity but comprises multiple lineages with distinct genome content and disease associations, raising the possibility that innate immune evasion mechanisms may not be equivalent across lineage. In the current article, we conducted a comprehensive review of the literature, focusing on the innate response developed mainly by phagocytes against this Gram-positive bacterium. Our aim was to summarize the last findings and to identify the main gaps in knowledge to guide future research efforts toward areas that require further investigation.

Porcine reproductive and respiratory syndrome (PRRS), caused by the PRRS virus (PRRSV), remains one of the most economically significant infectious diseases affecting the global swine industry, resulting in annual losses exceeding US $1.2 billion in the USA alone. PRRSV infects porcine alveolar macrophages (PAMs) and induces profound mitochondrial dysfunction, leading to the release of mitochondrial DNA (mtDNA). However, the mechanisms by which PRRSV-induced mitochondrial damage acts as a damage-associated molecular pattern (DAMP) to trigger inflammatory responses have not been fully elucidated. Here, we report that highly pathogenic PRRSV (HP-PRRSV) infection upregulates interleukin-1β (IL-1β) messenger RNA (mRNA) expression and protein secretion in a dose- and time-dependent manner. Transmission electron microscopy revealed progressive mitochondrial swelling, cristae disorganization, and matrix loss during HP-PRRSV infection. Using RNAscope combined with MitoGreen staining, we discovered that mitochondrial double-stranded RNA (mtdsRNA), generated from bidirectional transcription of mitochondrial DNA, is released into the cytosol during PRRSV infection. In vitro, transcription-driven mtdsRNA or mtdsRNA isolated from PAMs directly activated the NLRP3 inflammasome, inducing caspase-1 cleavage and IL-1β secretion. Mechanistically, the PRRSV-encoded nonstructural protein 11 (nsp11) inhibited NLRP3-dependent inflammatory responses by suppressing the oligomerization of the apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD) (ASC), thereby constraining excessive inflammation and establishing a delicate balance between pro-inflammatory signaling and viral immune evasion. Collectively, our findings identify mtdsRNA as a previously unrecognized mitochondrial DAMP that links PRRSV-induced mitochondrial injury to NLRP3 inflammasome activation, while also revealing a counter-regulatory role for nsp11 in modulating inflammation.

Bovine coronavirus (BCoV), a primary etiological agent of calf diarrhea, exhibits dual tropism for the respiratory and enteric tracts. However, research on BCoV gene function and pathogenesis has been limited by the lack of convenient and flexible reverse genetics tools. Herein, we report a robust reverse genetics system for BCoV based on an optimized circular polymerase extension reaction (CPER) methodology. We successfully rescued recombinant BCoV (rBCoV) in HRT-18G cells and engineered recombinant BCoV expressing ZsGreen fluorescent protein (rBCoV/Zs-T2A-ns2). Phenotypic analysis demonstrated that both unmodified rBCoV and rBCoV/Zs-T2A-ns2 maintained growth kinetics comparable to the wild-type BCoV. Importantly, the reporter virus demonstrated remarkable genetic stability for over ten passages, identifying the ns2 locus as a suitable insertion site for stable foreign gene expression without compromising viral fitness or sequence integrity. As a proof-of-concept application, the rBCoV/Zs-T2A-ns2 was employed for antiviral compound evaluation, successfully identifying four compounds-camostat, nafamostat, niclosamide, and nelfinavir-capable of effectively inhibiting BCoV replication. Further time-of-addition assays revealed that nelfinavir and niclosamide targeted the BCoV replication stage, while camostat and nafamostat interfered with BCoV internalization. This versatile CPER-based reverse genetics system provides a critical platform for advanced BCoV pathogenesis research and accelerated development of novel vaccines and effective antiviral therapeutics, ultimately contributing to enhanced bovine health and sustainable livestock production.

Enterococcus spp. from food animals represent important reservoirs of antimicrobial resistance; however, the mechanisms underlying tigecycline resistance remain poorly understood. In this study, we investigated the genetic basis and evolutionary dynamics of tigecycline resistance in Enterococcus hirae. Among 118 Enterococcus isolates recovered from 150 swine-derived samples, E. hirae was the predominant species (68/118, 57.63%). Tigecycline resistance was identified in ten isolates (10/118, 8.47%), all belonging to a single E. hirae clone. Whole-genome sequencing of a representative isolate, EG2361, revealed three plasmids, among which pEG2361-2 harbored an IS1216E-associated multidrug resistance region capable of generating two circular translocatable units (TUs). TU1, carrying the promoter-variant tet(L) locus together with tet(M) and poxtA, underwent tandem amplification, leading to plasmid structural heterogeneity. Functional analyses demonstrated that tet(L) reduced tigecycline susceptibility, whereas enhanced resistance mainly associated with variation in the upstream promoter region rather than Tet(L) amino acid substitutions. Experimental evolution revealed a dynamic resistance trajectory. The initial increase in tigecycline resistance was associated with TU1 amplification and marked upregulation of tet(L) expression. Subsequently, tet(L) expression declined, whereas tigecycline minimum inhibitory concentrations (MICs) remained elevated and stable. Recurrent rpsJ mutations emerged independently across evolved lineages and were associated with high-level resistance. Together, these findings support a stepwise evolutionary model in which insertion sequence (IS)1216E-mediated amplification of the promoter-variant tet(L) locus drives rapid early adaptation, followed by the emergence of chromosomal rpsJ mutations associated with stable high-level resistance. This study expands current understanding of tigecycline resistance evolution in enterococci and highlights the interplay among mobile genetic elements, transcriptional regulation, and chromosomal adaptation in shaping antimicrobial resistance.

Bovine digital dermatitis (BDD) is a globally distributed infectious hoof disease that negatively impacts the wellbeing and productivity of the affected animal. Treponema species and in particular Treponema phagedenis are the microbes strongly associated with the disease. Recently, it has been reported that Bos indicus cattle are more resistant to BDD and to the colonization by Treponema phagedenis in contrast to many Bos taurus breeds. This study investigated whether Bos indicus mount a different immune response to Treponema phagedenis compared with Bos taurus cattle, to better understand the different disease outcome in the two subspecies. Therefore, we exposed freshly isolated primary bovine blood cells to Treponema phagedenis and dissected subsequent bovine immune responses. The comparison between the two subspecies revealed significant different immune responses to Treponema phagedenis. We observed a stronger Th1/proinflammatory cytokine induction in Bos taurus animals mainly driven by CD4[+] T and CD21[low] B cells in secreting IFN-γ. We assume that these distinct initial immune responses are linked to the control of Treponema phagedenis and the outcome of BDD. Additionally, we observed significant higher levels in the expression of the matrix metalloproteinase-9 by peripheral blood mononuclear cells in Bos indicus cattle, which likely benefits the host response to Treponema phagedenis.

Between 14 October 2024 and 24 March 2025, 43 cases of clade 2.3.4.4b highly pathogenic avian influenza (HPAI) type A (H5N1) infections in wild birds and 1 case in a leopard cat were detected through the national HPAI surveillance program. We performed whole-genome sequencing of 51 isolates and investigated their phylogenetic relationships. Phylogenetic analyses identified nine distinct genotypes, designated Kor24-25A to Kor24-25I. The most commonly detected genotype, Kor24-25A (n = 24), was frequently detected in Pelecaniformes and was most prevalent between December 2024 and January 2025. Bayesian continuous and discrete trait phylodynamic analyses using HA gene sequences identified the three most probable routes of viral introduction via Gyeonggi, Jeju, and the southern coastal areas of the Korean Peninsula and suggested that wild ducks served as the primary reservoirs facilitating viral transmission in the wild bird population. During the 2024-2025 season, great egrets (Ardea alba) appeared to be more frequently affected than other wild bird species, suggesting possible seasonal differences in species-specific disease outcomes among wild birds. This study provides valuable insights into the phylodynamics, host associations, and transmission patterns of HPAI H5N1 viruses. It emphasizes the importance of enhanced surveillance programs targeting key avian hosts and high-risk geographic areas.

Bovine viral diarrhea virus (BVDV) is an important infectious pathogen responsible for substantial economic losses in the global cattle industry. The structural protein E2 serves as a major protective antigen of BVDV and is the main target for host neutralizing immune responses. However, its antigenic structure and epitope distribution remain poorly understood. Here, five novel monoclonal antibodies (mAbs) against the E2 protein of BVDV-1 were generated using hybridoma technology, and their reactivity patterns, biological properties, and recognized epitopes were systematically characterized. As a result, one mAb, TBH033, specifically reacted with BVDV, while four mAbs, TBH002, TBH004, TBH008, and TBH009, exhibited broad-spectrum reactivity against different subgenotypes of classical swine fever virus (CSFV) and BVDV, as well as E2 proteins from eight pestivirus species (BVDV-1, BVDV-2, BVDV-3, CSFV, BDV, PPeV, GPeV, and ovIT PeV). All five mAbs exhibited high binding affinity to the E2 protein and potent cross-neutralizing activity against BVDV strains of different subgenotypes. Epitope mapping with chimeric recombinant and site-mutated E2 proteins revealed that TBH002, TBH004, TBH008, and TBH009 recognized a linear epitope in the DA domain, comprising [70]H, [72]R, [74]L and [76]T as critical residues; TBH033 targeted a BVDV-specific conformational epitope in the DB domain, defined by the conserved amino acid motifs [103]LCP[105], [123]GP[124]. These findings enrich our understanding of the antigenic structure of the E2 protein and may facilitate the design of E2-based diagnostic tools and vaccines.

Host defense peptides (HDPs) possess both direct bacteriocidal and immunomodulatory activities. In this study, chicken cathelicidin-1 (cCATH-1) and chicken cathelicidin-3 (cCATH-3) were selected based on their markedly different minimum inhibitory concentrations (MICs) against avian pathogenic Escherichia coli (APEC) strains, with MICs of cCATH-1 being 4- to 16-fold lower than those of cCATH-3. However, following intraperitoneal challenge with APEC strain E058 (4 × 10[6] CFU/mouse), 80% of cCATH-3 treated mice survived while 20% of cCATH-1 treated mice survived. Flow cytometry (FC) revealed significantly lower peripheral blood Ly6C[high] monocytes but higher peritoneal Ly6C[high] macrophages in cCATH-3-treated mice at 4 and 8 h post-treatment. Peritoneal CCL3 secretion was significantly upregulated in cCATH-3 treated mice at 8 h post-treatment. Upon knockout of macrophages, the protection of cCATH-3 in mice against APEC E058 challenge was markedly abolished. In vitro, peritoneal macrophages treated with cCATH-3 showed stronger bacteriocidal activity than those treated with cCATH-1. Mouse CCL-3 (mCCL3)-specific antibody neutralize the effect of mCCL3 on macrophages chemotaxis in vitro. mCCL3-specific antibody administration resulted in 0% survival in cCATH-3-treated mice versus 60% survival in cCATH-3-treated mice administered with mock antibody, while cCATH-1-treated mice showed 0% survival administered with either mCCL3-specific antibody or mock antibody after APEC E058 strain challenge. In summary, cCATH-3 provides robust protection against APEC infection compared with cCATH-1 in mice, partially through CCL3-mediated macrophage chemotaxis and enhanced bacteriocidal activity in activated macrophages, revealing a novel mechanism of avian cathelicidins and supporting HDPs as alternatives to antibiotics for controlling avian colibacillosis.