Transcriptome analysis reveals a new virulence-associated trimeric autotransporter responsible for Glaesserella parasuis autoagglutination.

Capsular polysaccharide is an important virulence factor of Glaesserella parasuis. An acapsular mutant displays multiple phenotype variations, while the underlying mechanism for these variations is unknown. In this study, we created an acapsular mutant by deleting the wza gene in the capsule locus. We then used transcriptome analysis to compare the gene expression profiles of the wza deletion mutant with those of the parental strain to understand the possible reasons for the phenotypic differences. The mutant Δwza, which has a deleted wza gene, secreted less polysaccharide and lost its capsule structure. The Δwza exhibited increased autoagglutination, biofilm formation and adherence to eukaryotic cells, while the complementary strain C-Δwza partially restored the phenotype. Transcriptome analysis revealed several differentially expressed genes (DEGs) in Δwza, including up-regulated outer membrane proteins and proteins involved in peptidoglycan biosynthesis, suggesting that wza deletion affects the cell wall homeostasis of G. parasuis. Transcriptome analysis revealed the contribution of non-coding RNAs in the regulation of DEGs. Moreover, a new virulence-associated trimeric autotransporter, VtaA31 is upregulated in Δwza. It is responsible for enhanced autoagglutination but not for enhanced biofilm formation and adherence to eukaryotic cells in Δwza. In conclusion, these data indicate that wza affects the expression of multiple genes, especially those related to cell wall synthesis. Furthermore, they provide evidence that vtaA31 is involved in the autoagglutination of G. parasuis.

Research progress into the principles and methods underlying capsular typing of Glaesserella parasuis.

Glaesserella parasuis (GPS) is an important bacterial pathogen of swine. Serotype identification has presented a bottleneck in GPS research since it was first identified as the pathogen causing Glässer's disease in pigs in 1910. This paper presents a systematic review of the history of the development and application of gel immunodiffusion (GID), indirect hemagglutination assay (IHA), and polymerase chain reaction (PCR) typing methods for GPS, and the discovery of their shared antigenic basis. It provides a systematic theoretical overview of the immunology and principles underlying the three typing methods and offers new ideas for research into the prevention and control of Glässer's disease. In 1992, GPS was first classified into serotypes 1-15 using GID based on GPS heat-stable antigens, but about 25% of the strains were found to be non-typeable, and the composition of their antigens for serotyping was unclear. In 2003, the IHA method was established based on saline-extracted antigens of GPS, whose sensitivity and typing rate were higher than for GID, although about 15% of strains were still found to be non-typeable. The results of IHA and GID typing are roughly consistent, since they share the same GPS surface polysaccharide serotyping antigens, although whether these are capsular polysaccharides, lipopolysaccharides, or other polysaccharides, remains to be determined. In 2013, the Capsular polysaccharide (CPS) synthetic gene clusters from GPS serotypes 1-15 were successfully analyzed, confirming that CPS is essential for the formation of antigens for serotyping. In 2015, primers were designed based on the specific target genes of GPS capsules to establish a PCR typing method (H-PCR) for GPS, which, however, could not identify serotypes 5 and 12. In 2017, a new PCR typing method (J-PCR) was established based on the specific target genes of GPS capsules, which could identify serotypes 5 and 12. A combination of the two PCR typing methods enables the typing of almost all GPS strains, and the consistency with GID and IHA was verified using molecular biological methods. The antigenic basis of the three typing methods was shown to involve the GPS capsule. PCR typing methods are characterized by simple operation, fast speed, and low cost, and can successfully solve many problems in GID and IHA serotyping, and so have become widely adopted.

A marker-free genetic manipulation method for Glaesserella parasuis strains developed by alternately culturing transformants at 37°C and 30°C.

BACKGROUND: Glaesserella parasuis (G. parasuis) is the causative agent of Glässer's disease, which causes significant economic losses in the swine industry. However, research on the pathogenesis of G. parasuis has been hampered by the lack of a simple and efficient marker-free knockout system. RESULTS: In this study, a marker-free knockout system was developed for G. parasuis using a temperature-sensitive vector. By alternating the incubation of transformants at 30°C and 37°C, we optimized the screening process for this system. The system was successfully applied to knockout the KanR cassette from JS0135ΔnanH::KanR, achieving a knockout efficiency of 90% in the final round of screening. To confirm that temperature variation was a key factor, we proceeded with knocking out the nanH and apd genes in the CF7066 strain. The knockout efficiency reached up to 100%, with the shortest screening time being only four days. The knockout of the nanH gene resulted in a significant reduction in the growth vitality of the strains, while the knockout of the apd gene led to an approximate 56% improvement in the adhesion rate. Additionally, we observed that the expression of recombinant genes in transformants was higher at 30℃ than at 37℃, with the recC gene being upregulated approximately 7-fold. In contrast, there was almost no difference in the expression of recombinant genes between 30℃ and 37℃ in the wild-type strains. This discrepancy was likely due to an elevated copy number of target plasmids at 30℃, which may have resulted in the enhanced expression of recombinant genes. CONCLUSIONS: In conclusion, this newly developed gene knockout system for G. parasuis presents a valuable tool for advancing research on this organism.

Genomic insight into the diversity of Glaesserella parasuis isolates from 19 countries.

Glaesserella parasuis is a commensal bacterial organism found in the upper respiratory tract of healthy pigs and the etiological agent of Glässer's disease, which causes severe economic losses in the swine industry. This study aimed to better understand the epidemiological characteristics of this opportunistic pathogen. We investigated the prevalence and distribution of sequence types (STs), serovars, antimicrobial resistance genes (ARGs), and potential virulence factors (VFs) in 764 G. parasuis isolates collected from diseased and healthy pigs from 19 countries, including China. Multilocus sequence typing showed a high degree of variation with 334 STs, of which 93 were not previously recognized. Phylogenetic analysis revealed two major clades distinguished by isolation year, source, country, and serovar. The dominant serovars of G. parasuis were serovars 4 (19.50%), 7 (15.97%), 5/12 (13.87%), and 13 (12.30%). Serovar 7 gradually became one of the dominant serovars in G. parasuis with more VFs and fewer ARGs. Serovars 4 and 5/12 were the most frequent serovars in diseased pigs, whereas serovars 2, 8, and 11 were predominant in healthy pigs. Serovars 7 and 13 possessed more VFs than the other serovars. This study provides novel insights into the global prevalence and epidemiology of G. parasuis and valuable clues for further investigation into the pathogenicity of G. parasuis, which will facilitate the development of effective vaccines.IMPORTANCEGlaesserella parasuis is a clinically important gram-negative opportunistic pathogen, which causes serious financial losses in swine industry on a global scale. No vaccine is known that provides cross-protection against all 15 serovars; furthermore, the correlation between serovar and virulence is largely unknown. This study provides a large number of sequenced strains in 19 countries and compares the genomic diversity of G. parasuis between diseased and healthy pigs. We found a slight change in the dominant serovar of G. parasuis in the world, with serovar 7 gradually emerging as one of the predominant serovars. The observed higher average number of VFs in this particular serovar strain challenges the previously held notion that serovar 7 is non-virulent, indicating a more complex virulence landscape than previously understood. Our analysis indicating that six ARGs [tet(B), sul2, aph(3')-Ia, aph (6)-Id, blaROB-1, and aph(3'')-Ib] are likely to be transmitted horizontally in their entirety. By analyzing VFs, we provided an improved understanding of the virulence of G. parasuis, and these key findings suggest that vaccine development will be challenging.

Transcriptome Analysis Reveals Novel Inflammatory Signalings to Glaesserella parasuis Infection.

Glaesserella parasuis (GPS) can cause severe systemic inflammation in pigs, resulting in huge economic losses to the pig industry. At present, no effective method is available for the prevention and control of GPS infection. Molecular breeding for disease resistance is imminent, but disease-resistance genes have not been identified. To study the mechanism of systemic acute inflammation caused by GPS, we established three in vitro infection models (3D4/21 cells, PK15 cells, and PAVEC cells) according to its infection path. There was no significant difference in apoptosis among the three kinds of cells after 12 h of continuous GPS stimulation, while inflammatory factors were significantly upregulated. Subsequent transcriptome analysis revealed 1969, 1207, and 3564 differentially expressed genes (DEGs) in 3D4/21 cells, PK15 cells, and PAVEC cells, respectively, after GPS infection. Many of the DEGs were predicted to be associated with inflammatory responses (C3, CD44, etc.); cell proliferation, growth and apoptosis; gene expression; and protein phosphorylation. Key signaling pathways, including S100 family signaling, bacteria and virus recognition, and pathogen-induced cytokine storm signaling, were enriched based on Ingenuity Pathway Analysis (IPA). Furthermore, a total of three putative transmembrane receptors and two putative G-protein-coupled receptors, namely F3, ICAM1, PLAUR, ACKR3, and GPRC5A, were identified by IPA among the three types of cells. ACKR3 and GPRC5A play pivotal roles in bacterial adhesion, invasion, host immune response and inflammatory response through the S100 family signaling pathway. Our findings provide new insights into the pathological mechanisms underlying systemic inflammation caused by GPS infection in pigs, and they lay a foundation for further research on disease-resistance breeding to GPS.

Histidine Kinase QseC in Glaesserella parasuis Enhances the Secretion of Proinflammatory Cytokines by Macrophages via the p38 and NF-κB Signaling Pathways.

The qseC gene is a two-component system that encodes a histidine protein kinase and is highly conserved among different Glaesserella parasuis strains. In this study, we used qRT-PCR and enzyme-linked immunosorbent assay to confirm that Toll-like receptor 4 (TLR4) plays a role in the expression of proinflammatory cytokines interleukin (IL)-1ß and IL-6 by stimulating RAW 264.7 macrophages with QseC. Furthermore, we revealed that blocking the p38 and NF-κB pathways that regulate signaling can significantly reduce the production of proinflammatory cytokines induced by QseC. In summary, our data suggest that QseC is a novel proinflammatory mediator that induces TLR4-dependent proinflammatory activity in RAW 264.7 macrophages through the p38 and NF-κB pathways.

The role of cytolethal distending toxin in Glaesserella parasuis JS0135 strain infection: Cytotoxicity, phagocytic resistance and pathogenicity.

Glaesserella parasuis is an important porcine pathogen that commonly colonizes the upper respiratory tract of pigs and is prone to causing Glässer's disease under complex conditions. As yet, the disease has led to serious economic losses to the swine industry worldwide. Studies so far have found that several virulence factors are associated with the pathogenicity of G. parasuis, but the pathogenic mechanism is still not fully understood. Cytolethal distending toxin (CDT), a potential virulence factor in G. parasuis, is involved in cytotoxicity, serum resistance, adherence to and invasion of host cells in vitro. Here, to further investigate the pathogenic role of CDT during G. parasuis infection in vitro and in vivo, a double cdt1 and cdt2 deletion mutant (Δcdt1Δcdt2) without selectable marker was first generated in G. parasuis JS0135 strain by continuous natural transformations and replica plating. Morphological observation and lactate dehydrogenase assay showed that the Δcdt1Δcdt2 mutant was defective in cytotoxicity. Additionally, the Δcdt1Δcdt2 mutant was more susceptible to phagocytosis caused by 3D4/2 macrophages compared to the wild-type JS0135 strain. Moreover, by focusing on clinical signs, necropsy, bacterial recovery and pathological observation, we found that the deletion of cdt1 and cdt2 genes led to a significant attenuation of virulence in G. parasuis. Taken together, these findings suggest that as an important virulence factor, CDT can significantly affect the pathogenicity of G. parasuis.

Expression profiles of miRNAs in the lung tissue of piglets infected with Glaesserella parasuis and the roles of ssc-miR-135 and ssc-miR-155-3p in the regulation of inflammation.

MicroRNAs (miRNAs) have been shown to play an important regulatory role in the process of pathogenic infection. However, the miRNAs that regulate the pathogenic process of G. parasuis and their functions are still unknown. Here, high-throughput sequencing was used to quantify the expression of miRNA in piglet lung tissue after G. parasuis XX0306 strain infection. A total of 25 differentially expressed microRNAs (DEmiRNAs) were identified. GO and KEGG pathway enrichment analysis showed that many of the functions of genes that may be regulated by DEmiRNA are related to inflammatory response and immune regulation. Further studies found that ssc-miR-135 may promote the expression of inflammatory factors through NF-κB signaling pathway. Whereas, ssc-miR-155-3p inhibited the inflammatory response induced by G. parasuis, and its regulatory mechanism remains to be further investigated. This study provides a valuable reference for revealing the regulatory effects of miRNAs on the pathogenesis of G. parasuis. DATA AVAILABILITY: The datasets generated during the current study are not publicly available due to this study is currently in the ongoing research stage, and some of the data cannot be made public sooner yet, but are available from the corresponding author on reasonable request.

Activation of the NLRP3-CASP-1 inflammasome is restrained by controlling autophagy during Glaesserella parasuis infection.

Infection with Glaesserella parasuis, the primary pathogen behind Glässer's disease, is often associated with diverse clinical symptoms, including serofibrinous polyserositis, arthritis, and meningitis. Autophagy plays a dual role in bacterial infections, exerting either antagonistic or synergistic effects depending on the nature of the pathogen. Our previous studies have demonstrated that autophagy serves as a defense mechanism, combating inflammation and invasion caused by infection of highly virulent G. parasuis. However, the precise mechanisms remain to be elucidated. Pathogens exhibit distinct interactions with inflammasomes and autophagy processes. Herein, we explored the effect of autophagy on inflammasomes during G. parasuis infection. We found that G. parasuis infection triggers NLRP3-dependent pro-CASP-1-IL-18/IL-1ß processing and maturation pathway, resulting in increased release of IL-1ß and IL-18. Inhibition of autophagy enhances NLRP3 inflammasome activity, whereas stimulation of autophagy restricts it during G. parasuis infection. Furthermore, assembled NLRP3 inflammasomes undergo ubiquitination and recruit the autophagic adaptor, p62, facilitating their sequestration into autophagosomes during G. parasuis infection. These results suggest that the induction of autophagy mitigates inflammation by eliminating overactive NLRP3 inflammasomes during G. parasuis infection. Our research uncovers a mechanism whereby G. parasuis infection initiates inflammatory responses by promoting the assembly of the NLRP3 inflammasomes and activating NLRP3-CASP-1, both of which processes are downregulated by autophagy. This suggests that pharmacological manipulation of autophagy could be a promising approach to modulate G. parasuis-induced inflammatory responses.

Evaluation of immunoregulation and immunoprotective efficacy of Glaesserella parasuis histidine kinase QseC.

QseC is a membrane sensor kinase that enables bacteria to perceive autoinducers -3, adrenaline, and norepinephrine to initiate downstream gene transcription. In this study, we found that the QseC protein of Glaesserella parasuis can serve as an effective antigen to activate the host's immune response. Therefore, we investigated the immunogenicity and host protective effect of this protein. ELISA and indirect immunofluorescence results showed that QseC protein can induce high titer levels of humoral immunity in mice and regularly generate specific serum antibodies. We used MTS reagents to detect lymphocyte proliferation levels and found that QseC protein can cause splenic lymphocyte proliferation with memory and specificity. Further immunological analysis of the spleen cell supernatant revealed significant upregulation of levels of IL-1ß, IL-4 and IFN-γ in the QseC + adjuvant group. In the mouse challenge experiment, it was found that QseC + adjuvant can provide effective protection. The results of this study demonstrate that QseC protein provides effective protection in a mouse model and has the potential to serve as a candidate antigen for a novel subunit vaccine for further research.

AMPK signaling pathway regulated the expression of the ApoA1 gene via the transcription factor Egr1 during G. parasuis stimulation.

Glaesserella parasuis (G. parasuis) is the causative agent of porcine Glässer's disease, resulting in high mortality rates in pigs due to excessive inflammation-induced tissue damage. Previous studies investigating the protective effects of G. parasuis vaccination indicated a possible role of ApoA1 in reflecting disease progression following G. parasuis infection. However, the mechanisms of ApoA1 expression and its role in these infections are not well understood. In this investigation, newborn porcine tracheal (NPTr) epithelial cells infected with G. parasuis were used to elucidate the molecular mechanism and role of ApoA1. The study revealed that the AMPK pathway activation inhibited ApoA1 expression in NPTr cells infected with G. parasuis for the first time. Furthermore, Egr1 was identified as a core transcription factor regulating ApoA1 expression using a CRISPR/Cas9-based system. Importantly, it was discovered that APOA1 protein significantly reduced apoptosis, pyroptosis, necroptosis, and inflammatory factors induced by G. parasuis in vivo. These findings not only enhance our understanding of ApoA1 in response to bacterial infections but also highlight its potential in mitigating tissue damage caused by G. parasuis infection.

Glaesserella parasuis serotype 5 induces pyroptosis via the RIG-I/MAVS/NLRP3 pathway in swine tracheal epithelial cells.

Glaesserella parasuis (G. parasuis) is a common Gram-negative commensal bacterium in the upper respiratory tract of swine that can cause Glässer's disease under stress conditions. Pyroptosis is an important immune defence mechanism of the body that plays a crucial role in clearing pathogen infections and endogenous danger signals. This study aimed to investigate the mechanism of G. parasuis serotype 5 SQ (GPS5-SQ)-induced pyroptosis in swine tracheal epithelial cells (STECs). The results of the present study demonstrated that GPS5-SQ infection induces pyroptosis in STECs by enhancing the protein level of the N-terminal domain of gasdermin D (GSDMD-N) and activating the NOD-like receptor protein 3 (NLRP3) inflammasome. Furthermore, the levels of pyroptosis-related proteins, including GSDMD-N and cleaved caspase-1 were considerably decreased in STECs after the knockdown of retinoic acid inducible gene-I (RIG-I) and mitochondrial antiviral signaling protein (MAVS). These results indicated that GPS5-SQ might trigger pyroptosis through the activation of the RIG-I/MAVS/NLRP3 signaling pathway. More importantly, the reactive oxygen species (ROS) scavenger N-acetylcysteine (NAC) repressed the activation of the RIG-I/MAVS/NLRP3 signaling and rescued the decrease in Occludin and zonula occludens-1 (ZO-1) after GPS5-SQ infection. Overall, our findings show that GPS5-SQ can activate RIG-I/MAVS/NLRP3 signaling and destroy the integrity of the epithelial barrier by inducing ROS generation in STECs, shedding new light on G. parasuis pathogenesis.

EspP2 Regulates the Adhesion of Glaesserella parasuis via Rap1 Signaling Pathway.

Different levels of EspP2 expression are seen in strains of Glaesserella parasuis with high and low pathogenicity. As a potential virulence factor for G. parasuis, the pathogenic mechanism of EspP2 in infection of host cells is not clear. To begin to elucidate the effect of EspP2 on virulence, we used G. parasuis SC1401 in its wild-type form and SC1401, which was made EspP2-deficient. We demonstrated that EspP2 causes up-regulation of claudin-1 and occludin expression, thereby promoting the adhesion of G. parasuis to host cells; EspP2-deficiency resulted in significantly reduced adhesion of G. parasuis to cells. Transcriptome sequencing analysis of EspP2-treated PK15 cells revealed that the Rap1 signaling pathway is stimulated by EspP2. Blocking this pathway diminished occludin expression and adhesion. These results indicated that EspP2 regulates the adhesion of Glaesserella parasuis via Rap1 signaling pathway.

Application of a rapid and sensitive RPA-CRISPR/Cas12a assay for naked-eye detection of Haemophilus parasuis.

BACKGROUND: Haemophilus parasuis (H. parasuis) is a gram-negative bacterial pathogen that causes severe infections in swine, resulting in substantial economic losses. Currently, the majority of H. parasuis detection methods are impractical for on-site application due to their reliance on large instruments or complex procedures. Thus, there is an urgent need to develop a rapid, visually detectable, and highly sensitive detection method, especially under resource-limited environments and field conditions. RESULTS: In this study, we established a naked eye assay for highly sensitive detection by combining recombinase polymerase amplification (RPA) with CRISPR/Cas12a technology. Positive samples exhibited a clear red color visible to the naked eye, while negative samples appeared blue. We achieved a remarkable sensitivity, detecting H. parasuis down to a single copy, with no cross-reactivity with other bacteria. In a mouse model, our assay detected H. parasuis infection nearly 8 h earlier than traditional PCR. Compared to qPCR, our detection results were 100 % accurate. To enhance point-of-care applicability and mitigate the risk of aerosol contamination from uncapping, we consolidated RPA and CRISPR/Cas12a cleavage into a single-tube reaction system. This integrated approach was validated with 20 clinical lung samples, yielding results consistent with those obtained from qPCR. The entire procedure, from DNA extraction to detection, was completed in 35 min. SIGNIFICANCE: We present an RPA-CRISPR/Cas12a assay suitable for the early and resource-efficient diagnosis of H. parasuis infections. Its simplicity and visual detection are advantageous for field diagnostics, representing a substantial develpoment in the diagnosis of H. parasuis.

Preliminary view of the distribution and spread of the plasmid-mediated resistance genes in Glaesserella parasuis.

Introduction. Various plasmid-mediated resistance genes have been reported in Glaesserella parasuis, but little is known about their global distribution features, evolution pattern and spread.Gap Statement. The potential mobilization mechanisms of resistance plasmids in G. parasuis have been poorly explored.Aim. The aim of the study was to investigate the prevalence and diversity of plasmid-mediated resistance genes among G. parasuis isolates, and focus on the analysis of the features of the resistance plasmids from G. parasuis.Method. The plasmids tested were sequenced using the Illumina HiSeq platform in conjunction with PCR and inverted PCR. The susceptibility of the host strains was determined by broth microdilution. The transfer of plasmids tested was conducted by electroporation. The sequence data were compared using bioinformatics tools and the data from our laboratory and the National Center for Biotechnology Information (NCBI) database.Results. Nineteen plasmids were identified from our laboratory and these resistance plasmids were functional and transferable. Moreover, we clustered five types of genetic backbones of plasmids from G. parasuis and revealed the global distribution features of the plasmid-mediated resistance genes.Conclusions. This is the first report of the coexistence of tet(H)-bearing type I plasmid and lnu(C)-bearing type II plasmid in one G. parasuis clinical isolate. In addition, this study provides the first view of the global distribution of plasmid-mediated resistance genes and classifies the plasmids in G. parasuis according to their backbone regions.

Upregulation of occludin by cytolethal distending toxin facilitates Glaesserella parasuis adhesion to respiratory tract cells.

Virulent Glaesserella parasuis may engender systemic infection characterized by fibrinous polyserositis and pneumonia. G. parasuis causes systemic disease through upper respiratory tract infection, but the mechanism has not been fully characterized. Tight junction (TJ) proteins maintain the integrity and impermeability of the epithelial barriers. In this work, we applied the recombinant cytolethal distending toxin (CDT) holotoxin and cdt-deficient mutants to assess whether CDT interacted with TJ proteins of airway tract cells. Our results indicated that CDT induced the TJ occludin (OCLN) expression in newborn pig tracheal epithelial cells within the first 3 hours of bacterial infection, followed by a significant decrease. Overexpression of OCLN in target cells made them more susceptible to G. parasuis adhesion, whereas ablation of OCLN expression by CRISPR/Cas 9 gene editing technology in target cells decreased their susceptibility to bacterial adhesion. In addition, CDT treatment could upregulate the OCLN levels in the lung tissue of C57/BL6 mice. In summary, highly virulent G. parasuis strain SC1401 stimulated the tight junction expression, resulting in higher bacterial adhesion to respiratory tract cells, and this process is closely related to CDT. Our results may provide novel insights into G. parasuis infection and CDT-mediated pathogenesis.

Serotypes, virulence factors and multilocus sequence typing of Glaesserella parasuis from diseased pigs in Taiwan.

Background: Glaesserella parasuis (G. parasuis) belongs to the normal microbiota of the upper respiratory tract in the swine, but virulent strains can cause systemic infections commonly known as Glässer's disease that leads to significant economic loss in the swine industry. Fifteen serotypes of G. parasuis have been classified by gel immunodiffusion test while the molecular serotyping based on variation within the capsule loci have further improved the serotype determination of unidentified field strains. Serovar has been commonly used as an indicator of virulence; however, virulence can be significantly differ in the field isolates with the same serotype. To date, investigations of G. parasuis isolated in Taiwan regarding antimicrobial resistance, serotypes, genotypes and virulence factors remain unclear. Methods: A total of 276 G.parasuis field isolates were collected from 263 diseased pigs at the Animal Disease Diagnostic Center of National Chiayi University in Taiwan from January 2013 to July 2021. Putative virulence factors and serotypes of the isolates were identified by polymerase chain reaction (PCR) and antimicrobial susceptibility testing was performed by microbroth dilution assay. Additionally, the epidemiology of G. parasuis was characterized by multilocus sequence typing (MLST). Results: Serotype 4 (33.3%) and 5 (21.4%) were the most prevalent, followed by nontypable isolates (15.9%), serotype 13 (9.4%), 12 (6.5%), 14 (6.2%), 7 (3.3%), 1 (1.8%), 9 (1.1%), 11 (0.7%) and 6 (0.4%). Nine out of 10 putative virulence factors showed high positive rates, including group 1 vtaA (100%), fhuA (80.4%), hhdA (98.6%), hhdB (96.0%), sclB7 (99.6%), sclB11 (94.9%), nhaC (98.2%), HAPS_0254 (85.9%), and cirA (99.3%). According to the results of antimicrobial susceptibility testing, ceftiofur and florfenicol were highly susceptible (>90%). Notably, 68.8% isolates showed multidrug resistance. MLST revealed 16 new alleles and 67 new sequence types (STs). STs of these isolated G. parasuis strains were classified into three clonal complexes and 45 singletons by Based Upon Related Sequence Types (BURST) analysis. All the G. parasuis strains in PubMLST database, including strains from the diseased pigs in the study, were defined into two main clusters by Unweighted Pair Group Method with Arithmetic Mean (UPGMA). Most isolates in this study and virulent isolates from the database were mainly located in cluster 2, while cluster 1 included a high percentage of nasal isolates from asymptomatic carriers. In conclusion, this study provides current prevalence and antimicrobial susceptibility of G. parasuis in Taiwan, which can be used in clinical diagnosis and treatment of Glässer's disease.

Glaesserella parasuis QseBC two-component system senses epinephrine and regulates capD expression.

IMPORTANCE: The key bacterial pathogen Glaesserella parasuis, which can cause Glässer's disease, has caused significant financial losses to the swine industry worldwide. Capsular polysaccharide (CPS) is an important virulence factor for bacteria, providing the ability to avoid recognition and killing by the host immune system. Exploring the alteration of CPS synthesis in G. parasuis in response to epinephrine stimulation can lay the groundwork for revealing the pathogenic mechanism of G. parasuis as well as providing ideas for Glässer's disease control.

Molecular characterization of Glaesserella parasuis strains circulating in North American swine production systems.

BACKGROUND: Glaesserella parasuis is the causative agent of Glässer's disease in pigs. Serotyping is the most common method used to type G. parasuis isolates. However, the high number of non-typables (NT) and low discriminatory power make serotyping problematic. In this study, 218 field clinical isolates and 15 G. parasuis reference strains were whole-genome sequenced (WGS). Multilocus sequence types (MLST), serotypes, core-genome phylogeny, antimicrobial resistance (AMR) genes, and putative virulence gene information was extracted. RESULTS: In silico WGS serotyping identified 11 of 15 serotypes. The most frequently detected serotypes were 7, 13, 4, and 2. MLST identified 72 sequence types (STs), of which 66 were novel. The most predominant ST was ST454. Core-genome phylogeny depicted 3 primary lineages (LI, LII, and LIII), with LIIIA sublineage isolates lacking all vtaA genes, based on the structure of the phylogenetic tree and the number of virulence genes. At least one group 1 vtaA virulence genes were observed in most isolates (97.2%), except for serotype 8 (ST299 and ST406), 15 (ST408 and ST552) and NT (ST448). A few group 1 vtaA genes were significantly associated with certain serotypes or STs. The putative virulence gene lsgB, was detected in 8.3% of the isolates which were predominantly of serotype 5/12. While most isolates carried the bcr, ksgA, and bacA genes, the following antimicrobial resistant genes were detected in lower frequency;  blaZ (6.9%), tetM (3.7%), spc (3.7%), tetB (2.8%), bla-ROB-1 (1.8%), ermA (1.8%), strA (1.4%), qnrB (0.5%), and aph3''Ia (0.5%).   CONCLUSION: This study showed the use of WGS to type G. parasuis isolates and can be considered an alternative to the more labor-intensive and traditional serotyping and standard MLST. Core-genome phylogeny provided the best strain discrimination. These findings will lead to a better understanding of the molecular epidemiology and virulence in G. parasuis that can be applied to the future development of diagnostic tools, autogenous vaccines, evaluation of antibiotic use, prevention, and disease control.

Virulence assessment of four Glaesserella parasuis strains isolated in Liaoning province of China.

Glaesserella parasuis (G. parasuis) is a part of the normal upper respiratory microbiota of healthy swine. In many studies, the serovars 1, 4, 5, and 12 of G. parasuis are considered to be highly virulent and its serovars 3, 6, 7, 9, and 11 are considered to be non-virulent. Until now, researchers have found that non-virulent strains of G. parasuis cause an increasing number of diseases. However, little is known concerning why non-virulent strains cause disease with the virulence changes. In present study, four G. parasuis strains were evaluated for their cytotoxicity property, which aims to compare their virulence. The results showed that highly virulent strains XX0306 and CY1201, as well as, non-virulent strains HLD0115 and YK1603 caused a series of pathological changes, increased lactate dehydrogenase (LDH) release, and decreased cell activity. In addition, compared to the control group, both highly and non-virulent strains showed similar trends, demonstrating that the method of classifying the virulence of G. parasuis based on its serovar is worth further deliberation. Hence, we investigated the adhesion capacity and invasion rate of G. parasuis, the results indicated that XX0306 and HLD0115 had the strongest adhesion and invasion ability, which contradicts the classification of the virulence of G. parasuis based on its serovar. The apoptosis degree induced by highly virulent strains was more intensive than non-virulent strains, as measured by annexin V and propidium iodide (PI) double staining. Through testing the expression of apoptosis-related genes Bcl-2 and Bax, we found highly virulent strains induced apoptosis by inhibiting the expression of Bcl-2.