Investigation of Haemophilus parasuis from healthy pigs in China

Development of a Triplex qPCR Assay Based on the TaqMan Probe for the Detection of Haemophilus parasuis, Streptococcus suis Serotype 2 and Pasteurella multocida

Porcine respiratory disease is a significant economic problem for the global swine industry. Haemophilus parasuis (H. parasuis), Streptococcus suis (S. suis), and Pasteurella multocida (P. multocida) are three important pathogenic bacteria of the swine respiratory tract. Notably, the three pathogens not only frequently manifest as mixed infections, but their striking clinical similarities also present difficulties for pig populations in terms of disease prevention and treatment. Thus, we developed a triplex real-time quantitative polymerase chain reaction (qPCR) assay based on a TaqMan probe for the detection of H. parasuis, S. suis serotype 2, and P. multocida. Primers and probes were designed to target the conserved regions of the H. parasuis OmpP2 gene, the S. suis serotype 2 gdh gene, and the P. multocida Kmt1 gene. By optimizing the reaction system and conditions, a triplex qPCR method for simultaneous detection of H. parasuis, S. suis serotype 2, and P. multocida was successfully established. The amplification efficiencies of the standard curves for all three pathogens were found to be highly similar, with values of 102.105% for H. parasuis, 105.297% for S. suis serotype 2, and 104.829% for P. multocida, and all R2 values achieving 0.999. The specificity analysis results showed that the triplex qPCR method had a strong specificity. The sensitivity test results indicated that the limit of detection can reach 50 copies/μL for all three pathogens. Both intra- and inter-assay coefficients of variation for repeatability were below 1%. This triplex qPCR method was shown to have good specificity, sensitivity, and reproducibility. Finally, the triplex qPCR method established in this study was compared with the nested PCR as recommended by the Chinese national standard (GB/T34750-2017) for H. parasuis, the PCR as recommended by the Chinese national standard (GB/T 19915.9-2005) for S. suis serotype 2, and the PCR as recommended by the Chinese agricultural industry standard (NY/T 564-2016) for P. multocida by detecting the same clinical samples. Both methods are reasonably consistent, while the triplex qPCR assay was more sensitive. In summary, triplex qPCR serves not only as a rapid and accurate detection and early prevention method for these pathogens but also constitutes a robust tool for microbial quality control in specific pathogen-free pigs.

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.

Virulence and Antimicrobial Resistance Characterization of Glaesserella parasuis Isolates Recovered from Spanish Swine Farms

Glaesserella (Haemophilus) parasuis, the causative agent of Glässer's disease, is present in most pig farms as an early colonizer of the upper respiratory tract. It exhibits remarkable variability in virulence and antimicrobial resistance (AMR), with virulent strains capable of inducing respiratory or systemic disease. This study aimed to characterize the virulence and the AMR profiles in 65 G. parasuis isolates recovered from Spanish swine farms. Virulence was assessed using multiplex leader sequence (LS)-PCR targeting vtaA genes, with all isolates identified as clinical (presumed virulent). Pathotyping based on ten pangenome genes revealed the virulent HPS_22970 as the most frequent (83.1%). Diverse pathotype profiles were observed, with 29 unique gene combinations and two isolates carrying only potentially non-virulent pangenome genes. AMR phenotyping showed widespread resistance, with 63.3% classified as multidrug resistant, and high resistance to clindamycin (98.3%) and tylosin (93.3%). A very strong association was found between certain pathotype genes and AMR phenotypes, notably between the virulent HPS_22970 and tetracycline resistance (p < 0.001; Φ = 0.58). This study reveals the wide diversity and complexity of G. parasuis pathogenicity and AMR phenotype, emphasizing the need for the targeted characterization of clinical isolates to ensure appropriate antimicrobial treatments and the implementation of prophylactic measures against virulent strains.

HbpA from Glaesserella parasuis induces an inflammatory response in 3D4/21 cells by activating the MAPK and NF-κB signalling pathways and protects mice against G. parasuis when used as an immunogen

Glaesserella parasuis is usually a benign swine commensal in the upper respiratory tract, but virulent strains can cause systemic infection characterized by pneumonia, meningitis, and fibrinous polyserositis. The intensive pulmonary inflammatory response following G. parasuis infection is the main cause of lung injury and death in pigs. Vaccination has failed to control the disease due to the lack of extended cross-protection. Accumulating evidence indicates that the heme-binding protein A (HbpA) is a potential virulence determinant and a promising antigen candidate for the development of a broader range of vaccines. However, it is not yet known whether HbpA contributes to G. parasuis virulence or has any potential immune protective effects against G. parasuis. Here, we show that HbpA can induce the transcription and secretion of proinflammatory cytokines (IL-6, TNF-α, and MCP-1) in porcine alveolar macrophages (PAM, 3D4/31). The HbpA protein is recognized by Toll-like receptors 2 and 4 on 3D4/21 macrophages, resulting in the activation of MAP kinase and NF-κB signalling cascades and the transcription and secretion of proinflammatory cytokines. HbpA contributes to virulence and bacterial pulmonary colonization in C57BL/6 mice and plays a role in adhesion to host cells and evasion of the bactericidal effect of pulmonary macrophages. In addition, mice immunized with HbpA were partially protected against challenge by G. parasuis SC1401. The results suggest that HbpA plays an important role in the pathogenesis of disease caused by G. parasuis and lay a foundation for the development of a subunit or chimeric anti-G. parasuis vaccine.

Detection and differentiation of seven porcine respiratory pathogens using a multiplex ligation-dependent probe amplification assay

Respiratory diseases due to viral or bacterial agents, either alone or in combination, cause substantial economic burdens to the swine industry worldwide. Rapid and reliable detection of causal pathogens is crucial for effective epidemiological surveillance and disease management. This research aimed to employ the multiplex ligation-dependent probe amplification (MLPA) assay for simultaneous detection of seven distinct pathogens causing respiratory problems in swine, porcine reproductive and respiratory syndrome virus (PRRSV), swine influenza virus (SIV), porcine respiratory coronavirus (PRCV), porcine circovirus type 2 (PCV2), Pasteurella multocida, Actinobacillus pleuropneumoniae, and Glässerella parasuis. The results indicated no probe cross-reactivity among the seven target agents with other swine pathogens. The detection limits ranged from 5 to 34 copies per assay for the target organisms. The MLPA assay was evaluated with 88 samples and compared to real-time or multiplex PCR for the target pathogens. The MLPA assay demonstrated high relative test sensitivities (100 %) and reasonable to good relative specificities at 62.5 %, 95.1 %, 86.8 %, and 97.6 % for PRRSV, P. multocida, G. parasuis, and PCV2, respectively, relative to comparator PCR assays. In 71 samples where MLPA and comparator PCR assays matched exactly, infections were detected in 64 samples (90.1 %), with PRRSV being the most commonly found virus and 50.7 % of the samples showing co-infection with two to five of the pathogens. This approach serves as a valuable tool for conducting differential diagnoses and epidemiological investigations of pathogen prevalence within swine populations.

A physiologically based pharmacokinetic model to optimize the dosage regimen and withdrawal time of cefquinome in pigs

Cefquinome is widely used to treat respiratory tract diseases of swine. While extra-label dosages of cefquinome could improve clinical efficacy, they might lead to excessively high residues in animal-derived food. In this study, a physiologically based pharmacokinetic (PBPK) model was calibrated based on the published data and a microdialysis experiment to assess the dosage efficiency and food safety. For the microdialysis experiment, in vitro/in vivo relative recovery and concentration-time curves of cefquinome in the lung interstitium were investigated. This PBPK model is available to predict the drug concentrations in the muscle, kidney, liver, plasma, and lung interstitial fluid. Concentration-time curves of 1000 virtual animals in different tissues were simulated by applying sensitivity and Monte Carlo analyses. By integrating pharmacokinetic/pharmacodynamic target parameters, cefquinome delivered at 3-5 mg/kg twice daily is advised for the effective control of respiratory tract infections of nursery pig, which the bodyweight is around 25 kg. Based on the predicted cefquinome concentrations in edible tissues, the withdrawal interval is 2 and 3 days for label and the extra-label doses, respectively. This study provides a useful tool to optimize the dosage regimen of cefquinome against respiratory tract infections and predicts the concentration of cefquinome residues in edible tissues. This information would be helpful to improve the food safety and guide rational drug usage.

Secondary Highly Pathogenic Porcine Reproductive and Respiratory Syndrome Virus (HP-PRRSV2) Infection Augments Inflammatory Responses, Clinical Outcomes, and Pathogen Load in Glaesserella-parasuis-Infected Piglets

Glaesserella parasuis (Gps), Gram-negative bacteria, are a universal respiratory-disease-causing pathogen in swine that colonize the upper respiratory tract. Highly Pathogenic Porcine Reproductive and Respiratory Syndrome Virus (HP-PRRSV2HP-PRRSV2) and Gps coinfections are epidemics in China, but little is known about the influence of concurrent coinfection on disease severity and inflammatory responses. Herein, we studied the effects of secondary HP-PRRS infection on clinical symptoms, pathological changes, pathogen load, and inflammatory response of Gps coinfection in the upper respiratory tract of piglets. All coinfected piglets (HP-PRRSV2 + Gps) displayed fever and severe lesions in the lungs, while fever was present in only a few animals with a single infection (HP-PRRSV2 or Gps). Additionally, HP-PRRSV2 and Gps loading in nasal swabs and blood and lung tissue samples was significantly increased in the coinfected group. Necropsy data showed that coinfected piglets suffered from severe lung damage and had significantly higher antibody titers of HP-PRRSV2 or Gps than single-infected piglets. Moreover, the serum and lung concentrations of inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-8) were also significantly higher in coinfected piglets than in those infected with HP-PRRSV2 or Gps alone. In conclusion, our results show that HP-PRRSV2 promotes the shedding and replication of Gps, and their coinfection in the upper respiratory tract aggravates the clinical symptoms and inflammatory responses, causing lung damage. Therefore, in the unavoidable situation of Gps infection in piglets, necessary measures must be made to prevent and control secondary infection with HP-PRRSV2, which can save huge economic losses to the pork industry.

Upregulation of TLR4-Dependent ATP Production Is Critical for Glaesserella parasuis LPS-Mediated Inflammation

Glaesserella parasuis (G. parasuis), an important pathogenic bacterium, cause Glässer's disease, and has resulted in tremendous economic losses to the global swine industry. G. parasuis infection causes typical acute systemic inflammation. However, the molecular details of how the host modulates the acute inflammatory response induced by G. parasuis are largely unknown. In this study, we found that G. parasuis LZ and LPS both enhanced the mortality of PAM cells, and at the same time, the level of ATP was enhanced. LPS treatment significantly increased the expressions of IL-1β, P2X7R, NLRP3, NF-κB, p-NF-κB, and GSDMD, leading to pyroptosis. Furthermore, these proteins' expression was enhanced following extracellular ATP further stimulation. When reduced the production of P2X7R, NF-κB-NLRP3-GSDMS inflammasome signaling pathway was inhibited, and the mortality of cells was reduced. MCC950 treatment repressed the formation of inflammasome and reduced mortality. Further exploration found that the knockdown of TLR4 significantly reduced ATP content and cell mortality, and inhibited the expression of p-NF-κB and NLRP3. These findings suggested upregulation of TLR4-dependent ATP production is critical for G. parasuis LPS-mediated inflammation, provided new insights into the molecular pathways underlying the inflammatory response induced by G. parasuis, and offered a fresh perspective on therapeutic strategies.

Immunogenicity and protection against Glaesserella parasuis serotype 13 infection after vaccination with recombinant protein LolA in mice

Glaesserella parasuis is a pathogen causing Glässer's disease characterized by fibrinous polyserositis, polyarthritis, and meningitis. Owing to the low cross-immunogenicity of different bacterial antigens in commercial vaccines, finding and identifying effective immunoprotective antigens will facilitate the development of novel subunit vaccines. In this study, LolA, identified by bioinformatics approaches, was cloned and successfully expressed as a recombinant protein in Escherichia coli, and its immunogenicity and protection were evaluated in a mouse model. The results showed that the recombinant protein LolA can stimulate mice to produce high levels of IgG antibodies and confer 50% protection against challenge with the highly virulent G. parasuis CY1201 strain (serotype 13). By testing the cytokine levels of interleukin 4 (IL-4), IL-10, and interferon-γ (IFN-γ), it was found that the recombinant protein LolA can induce both Th1 and Th2 immune responses in mice. These results suggest that the recombinant protein LolA has the potential to serve as an alternative antigen for a novel vaccine to prevent G. parasuis infection.

Temporal Patterns of Phenotypic Antimicrobial Resistance and Coinfecting Pathogens in Glaesserella parasuis Strains Isolated from Diseased Swine in Germany from 2006 to 2021

Glaesserella parasuis (Gps) causes high economic losses in pig farms worldwide. So far no vaccine provides cross-protection for different serotypes, so antibiotic treatment is widely used to cope with this pathogen. In this study, routine diagnostic data from 2046 pigs with Gps related diseases sent for necropsy to a German laboratory in the time period 2006–2021 were analysed retrospectively. In the time period 2018–2021, the most frequent serotypes (ST) detected were ST4 (30%) and ST13 (22%). A comparison of the reference period 2006–2013 prior to obligatory routine recording of antimicrobial usage in livestock with the period 2014–2021 resulted in a statistically significant decrease of frequencies of resistant Gps isolates for ceftiofur, enrofloxacin, erythromycin, spectinomycin, tiamulin and tilmicosin. While in 2006–2013 all isolates were resistant for tetracyclin and cephalothin, frequencies of resistant isolates decreased in the second time period to 28% and 62%, respectively. Parallel to the reduction of antimicrobial usage, during recent years a reduction in resistant Gps isolates has been observed, so only a low risk of treatment failure exists. Most frequently, pigs positive for Gps were also positive for S.suis (25.4%), PRRSV-EU (25.1%) and influenza virus (23%). The viral pathogens may act as potential trigger factors.

Rational Use of Danofloxacin for Treatment of Mycoplasma gallisepticum in Chickens Based on the Clinical Breakpoint and Lung Microbiota Shift

The study was to explore the rational use of danofloxacin against Mycoplasma gallisepticum (MG) based on its clinical breakpoint (CBP) and the effect on lung microbiota. The CBP was established according to epidemiological cutoff value (ECV/CO_WT), pharmacokinetic–pharmacodynamic (PK–PD) cutoff value (CO_PD) and clinical cutoff value (CO_CL). The ECV was determined by the micro-broth dilution method and analyzed by ECOFFinder software. The CO_PD was determined according to PK–PD modeling of danofloxacin in infected lung tissue with Monte Carlo analysis. The CO_CL was performed based on the relationship between the minimum inhibitory concentration (MIC) and the possibility of cure (POC) from clinical trials. The CBP in infected lung tissue was 1 μg/mL according to CLSI M37-A3 decision tree. The 16S ribosomal RNA (rRNA) sequencing results showed that the lung microbiota, especially the phyla Firmicutes and Proteobacteria had changed significantly along with the process of cure regimen (the 24 h dosing interval of 16.60 mg/kg b.w for three consecutive days). Our study suggested that the rational use of danofloxacin for the treatment of MG infections should consider the MIC and effect of antibiotics on the respiratory microbiota.

Transcriptome profiling identifies immune response genes against porcine reproductive and respiratory syndrome virus and Haemophilus parasuis co-infection in the lungs of piglets

Background

Co-infections of the porcine reproductive and respiratory syndrome virus (PRRSV) and the Haemophilus parasuis (HPS) are severe in Chinese pigs, but the immune response genes against co-infected with 2 pathogens in the lungs have not been reported.

Objectives

To understand the effect of PRRSV and/or HPS infection on the genes expression associated with lung immune function.

Methods

The expression of the immune-related genes was analyzed using RNA-sequencing and bioinformatics. Differentially expressed genes (DEGs) were detected and identified by quantitative real-time polymerase chain reaction (qRT-PCR), immunohistochemistry (IHC) and western blotting assays.

Results

All experimental pigs showed clinical symptoms and lung lesions. RNA-seq analysis showed that 922 DEGs in co-challenged pigs were more than in the HPS group (709 DEGs) and the PRRSV group (676 DEGs). Eleven DEGs validated by qRT-PCR were consistent with the RNA sequencing results. Eleven common Kyoto Encyclopedia of Genes and Genomes pathways related to infection and immune were found in single-infected and co-challenged pigs, including autophagy, cytokine-cytokine receptor interaction, and antigen processing and presentation, involving different DEGs. A model of immune response to infection with PRRSV and HPS was predicted among the DEGs in the co-challenged pigs. Dual oxidase 1 (DUOX1) and interleukin-21 (IL21) were detected by IHC and western blot and showed significant differences between the co-challenged pigs and the controls.

Conclusions

These findings elucidated the transcriptome changes in the lungs after PRRSV and/or HPS infections, providing ideas for further study to inhibit ROS production and promote pulmonary fibrosis caused by co-challenging with PRRSV and HPS.

Investigation of morphological changes of HPS membrane caused by cecropin B through scanning electron microscopy and atomic force microscopy

Background

Antimicrobial peptides (AMPs) have been identified as promising compounds for consideration as novel antimicrobial agents.

Objectives

This study analyzed the efficacy of cecropin B against Haemophilus parasuis isolates through scanning electron microscopy (SEM) and atomic force microscopy (AFM) experiments.

Results

Cecropin B exhibited broad inhibition activity against 15 standard Haemophilus parasuis (HPS) strains and 5 of the clinical isolates had minimum inhibition concentrations (MICs) ranging from 2 to 16 μg/mL. Microelectrophoresis and hexadecane adsorption assays indicated that the more hydrophobic and the higher the isoelectric point (IEP) of the strain, the more sensitive it was to cecropin B. Through SEM, multiple blisters of various shapes and dents on the cell surface were observed. Protrusions and leakage were detected by AFM.

Conclusions

Based on the results, cecropin B could inhibit HPS via a pore-forming mechanism by interacting with the cytoplasmic membrane of bacteria. Moreover, as cecropin B concentration increased, the bacteria membrane was more seriously damaged. Thus, cecropin B could be developed as an effective anti-HPS agent for use in clinical applications.

Molecular characterization of Glaesserella parasuis strains isolated from North America, Europe and Asia by serotyping PCR and LS-PCR

Glaesserella parasuis strains were characterized by serotyping PCR, vtaA virulence marker Leader Sequence (LS)-PCR, clinical significance, and geographic region. Overall, the serovars 4, 5/12, 7, 1, and 13 were the most commonly detected. Serovars of greatest clinical relevance were systemic isolates that had a higher probability of being serovar 5/12, 13, or 7. In comparison, pulmonary isolates had a higher likelihood of being serovars 2, 4, 7, or 14. Serovars 5/12 and 13 have previously been considered disease-associated, but this study agrees with other recent studies showing that serovar 7 is indeed associated with systemic G. parasuis disease. Serovar 4 strains illustrated how isolates can have varying degrees of virulence and be obtained from pulmonary, systemic, or nasal sites. Serovars 8, 9, 15, and 10 were predominantly obtained from nasal samples, which indicates a limited clinical significance of these serovars. Additionally, most internal G. parasuis isolates were classified as virulent by LS-PCR and were disease-associated isolates, including serovars 1, 2, 4, 5/12, 7, 13, and 14. Isolates from the nasal cavity, including serovars 6, 9, 10, 11, and 15, were classified as non-virulent by LS-PCR. In conclusion, the distribution of G. parasuis serovars remains constant, with few serovars representing most of the strains isolated from affected pigs. Moreover, it was confirmed that the LS-PCR can be used for G. parasuis virulence prediction of field strains worldwide.

Biofilm characteristics and transcriptomic analysis of Haemophilus parasuis

Haemophilus parasuis (H. parasuis) is a conditional pathogen with the ability to form biofilms which can lead to ineffective drug treatment and severe chronic infections resulting in significant economic losses to the pig industry. Currently, knowledge of biofilm formation by H. parasuis is not well developed. The objective of this study was to investigate the three-dimensional morphology of biofilms and perform transcriptomic analysis on H. parasuis cells in biofilm versus planktonic forms. The results showed that proteins and DNA accounted for a large proportion of the H. parasuis biofilm extracellular matrix. Here, we have traced the entire biofilm formation process of H. parasuis from beginning to end for the first time. These biofilms grew rapidly in the first 48 h and became stable at 60 h. According to GO and KEGG analysis, the differentially expressed genes (DEG) artM, artQ, ssrS, pflA and HutX were implicated as being involved in bacterial colonisation and adhesion; these are the most likely genes to affect biofilm formation. Most functional gene enrichments were of those involved in metabolic pathways, biosynthesis of secondary metabolites, ATP-binding cassette (ABC) transporters, and starch and sucrose metabolism. Thus, in the present pilot study, the composition and characteristics of these biofilms were explored, and the genes related to biofilm formation were screened for. This research lays the foundation for further studies on mechanisms regulating biofilm formation, in order to find new drug targets and develop new therapeutic drugs against H. parasuis.

Sialidase of Glaesserella parasuis Augments Inflammatory Response via Desialylation and Abrogation of Negative Regulation of Siglec-5

Siglecs are sialic acid-binding immunoglobulin-like lectins that play an important role in tissue homeostasis, immune response, and pathogen infection. Bacterial sialidases act on natural ligands of Siglecs, interfering with the Siglec-mediated immune response. Glaesserella parasuis is a porcine bacterial pathogen that secretes sialidase. However, little is known about the sialidase of G. parasuis and its impact on immune regulation. Here, we used wild-type G. parasuis, a sialidase-deficient mutant, and complementary strains to investigate the role of sialidase in porcine alveolar macrophage infection. Sialidase induced the release of proinflammatory cytokines, such as interleukin-1α (IL-1α), IL-6, and tumor necrosis factor alpha, from porcine alveolar macrophages. Moreover, sialidase desialylated the surface of porcine alveolar macrophages and altered the expression of Siglecs (the expression of Siglec-5 was reduced). Furthermore, sialidase led to a reduction in endogenous SH2 domain-containing protein tyrosine phosphatase (SHP-2) recruitment to Siglec-5 and simultaneously activated the inflammatory response via the mitogen-activated protein kinase and nuclear factor kappa light chain enhancer of activated B cell signaling pathways. This desialylation occurred before the release of proinflammatory cytokines, suggesting that the sialidase-induced inflammatory response was followed by reduced recruitment of SHP-2 to Siglec-5. Thus, this study is the first to demonstrate the role of sialidase in the inflammatory response of G. parasuis. This role resulted from the abrogation of negative regulation of Siglec-5 on proinflammatory cytokine release. This study helps to understand the molecular mechanism underlying the inflammatory response induced by sialidase secreted by G. parasuis and the acute inflammation caused by G. parasuis.

Resident bacteria contribute to opportunistic infections of the respiratory tract

Opportunistic pathogens frequently cause volatile infections in hosts with compromised immune systems or a disrupted normal microbiota. The commensalism of diverse microorganisms contributes to colonization resistance, which prevents the expansion of opportunistic pathogens. Following microbiota disruption, pathogens promptly adapt to altered niches and obtain growth advantages. Nevertheless, whether and how resident bacteria modulate the growth dynamics of invasive pathogens and the eventual outcome of such infections are still unclear. Here, we utilized birds as a model animal and observed a resident bacterium exacerbating the invasion of Avibacterium paragallinarum (previously Haemophilus paragallinarum) in the respiratory tract. We first found that negligibly abundant Staphylococcus chromogenes, rather than Staphylococcus aureus, played a dominant role in Av. paragallinarum-associated infectious coryza in poultry based on epidemic investigations and in vitro analyses. Furthermore, we determined that S. chromogenes not only directly provides the necessary nutrition factor nicotinamide adenine dinucleotide (NAD⁺) but also accelerates its biosynthesis and release from host cells to promote the survival and growth of Av. paragallinarum. Last, we successfully intervened in Av. paragallinarum-associated infections in animal models using antibiotics that specifically target S. chromogenes. Our findings show that opportunistic pathogens can hijack commensal bacteria to initiate infection and expansion and suggest a new paradigm to ameliorate opportunistic infections by modulating the dynamics of resident bacteria.

There is an urgent need for novel intervention strategies and techniques to address the increasing dissemination of multidrug-resistant Gram-negative bacterial pathogens. More importantly, secondary bacterial infections are common in clinical practice, whereas the growth dynamics of each individual in such coinfections are still complicated and elusive. In the current study, we first identified Staphylococcus spp., especially negligibly abundant S. chromogenes, facilitating the pathogenesis of Av. paragallinarum, a Gram-negative bacterium responsible for severe and acute avian respiratory disease worldwide. Furthermore, we developed therapeutic strategies using specific antibiotics against Staphylococcus spp. to relieve clinical symptoms and reduce Av. paragallinarum-associated infections in chickens. These results show that implementation of a proper intervention strategy can prevent opportunistic infections by regulating the microbiota and elucidate the development of alternative approaches for treating Gram-negative pathogenic bacterial infections.

Deletion of Polyamine Transport Protein PotD Exacerbates Virulence in Glaesserella (Haemophilus) parasuis in the Form of Non-biofilm-generated Bacteria in a Murine Acute Infection Model

Polyamines are small, polycationic molecules with a hydrocarbon backbone and multiple amino groups required for optimal cell growth. The potD gene, belonging to the ABC (ATP-binding cassette) transport system potABCD, encodes the bacterial substrate-binding subunit of the polyamine transport system, playing a pivotal role in bacterial metabolism and growth. The swine pathogen Glaesserella parasuis possesses an intact pot operon, and the studies presented here mainly examined the involvement of PotD in Glaesserella pathogenesis. A potD-deficient mutant was constructed using a virulent G. parasuis strain SC1401 by natural transformation; immuno-electron microscopy was used to identify the subcellular location of native PotD protein; an electron microscope was adopted to inspect biofilm and bacterial morphology; immunofluorescence technique was employed to study cellular adhesion, the levels of inflammation and apoptosis. The TSA++-pre-cultured mutant strain showed a significantly reduced adhesion capacity to PK-15 and MLE-12 cells. Likewise, we also found attenuation in virulence using murine models focusing on the clinical sign, H&E, and IFA for inflammation and apoptosis. However, when the mutant was grown in TSB++, virulence recovered to normal levels, along with a high level of radical oxygen species formation in the host. The expression of PotD could actively stimulate the production of ROS in Raw 264.7. Our data suggested that PotD from G. parasuis has a high binding potential to polyamine, and is essential for the full bacterial virulence within mouse models. However, the virulence of the potD mutant is highly dependent on its TSA++ culture conditions rather than on biofilm-formation.

Serotyping and pathotyping of Glaesserella parasuis isolated 2012-2019 in Germany comparing different PCR-based methods

Glaesserella parasuis is an important pathogen in swine production. It acts as a primary pathogen in systemic Glässer´s disease and as a secondary pathogen in Porcine Respiratory Disease Complex. In this study, a collection of 308 isolates from carrier animals and individuals with respiratory or Glässer´s disease isolated 2012–2019 in Germany was analysed. Isolates were characterized for serovar implementing two different PCR methods. Additionally, two different PCR methods for pathotyping isolates were applied to the collection and results compared. Serovar 6 (p < 0.0001) and 9 (p = 0.0007) were correlated with carrier isolates and serovar 4 was associated with isolates from animals with respiratory disease (p = 0.015). In systemic isolates, serovar 13 was most frequently detected (18.9%). Various other serovars were isolated from all sites and the ratio of serovar 5 to serovar 12 was approximately 1:2. These two serovars together represented 14.3% of the isolates; only serovar 4 was isolated more frequently (24.7%). The pathotyping method based on the leader sequence (LS = ESPR of vta) was easy to perform and corresponded well to the clinical background information. Of the carrier isolates 72% were identified as non-virulent while 91% of the systemic isolates were classified as virulent (p < 0.0001). Results of the pathotyping PCR based on 10 different marker genes overall were in good agreement with clinical metadata as well as with results of the LS-PCR. However, the pathotyping PCR was more complicated to perform and analyze. In conclusion, a combination of the serotyping multiplex-PCR and the LS-PCR could improve identification of clinically relevant G. parasuis isolates, especially from respiratory samples.

Prevalence of Haemophilus parasuis"Glaesserella parasuis" in pigs in China: A systematic review and meta-analysis

Haemophilus parasuis, a gram-negative bacterium as an early commensal colonizer in the upper respiratory tract of weaning pigs (Sus scrofa), is one of the most important bacterial pathogens affecting pig populations. It is the causative agent of Glässer's disease, causing systemic infection and polyserositis, meningitis, and arthritis. H. parasuis infection can result in high mortality and morbidity with, the significant economic losses for pig producers. To estimate the overall disease prevalence of H. parasuis in pigs from China, we performed a meta-analysis using five bibliographical databases: PubMed, ScienceDirect, CNKI, Wanfang, and VIP Chinese Journal Databases. A total of 41 articles published between 2005 and 2019, fulfilled the final inclusion criteria. The overall prevalence of H. parasuis in pigs in China was 27.8 % with the highest prevalence between 2011 and 2015 (41.0 %). In terms of pig age, the point estimate of H. parasuis prevalence was higher in suckling piglets (29.2 %) compared with that for other pig ages. The prevalence in the serum subgroup (29.8 %) was higher than that in the nasal swab subgroup (12.5 %). The results of the present meta-analysis showed that H. parasuis infection was common in pig populations in China; therefore, effective control measures are necessary to reduce this threat to pig populations.

Update on Glässer's disease: How to control the disease under restrictive use of antimicrobials

Antimicrobials have been commonly used to control bacterial diseases in farm animals. The efficacy of these drugs deterred the development of other control measures, such as vaccines, which are currently getting more attention due to the increased concern about antimicrobial resistance. Glässer's disease is caused by Glaesserella (Haemophilus) parasuis and affects pork production around the world. Balance between colonization and immunity seems to be essential in disease control. Reduction in antimicrobial use in veterinary medicine requires the implementation of preventive measures, based on alternative tools such as vaccination and other strategies to guarantee a beneficial microbial colonization of the animals. The present review summarizes and discusses the current knowledge on diagnosis and control of Glässer's disease, including prospects on alternatives to antimicrobials.

Polyamine Transport Protein PotD Protects Mice against Haemophilus parasuis and Elevates the Secretion of Pro-Inflammatory Cytokines of Macrophage via JNK-MAPK and NF-κB Signal Pathways through TLR4

The potD gene, belonging to the well-conserved ABC (ATP-binding cassette) transport system potABCD, encodes the bacterial substrate-binding subunit of the polyamine transport system. In this study, we found PotD in Haemophilus (Glaesserella) parasuis could actively stimulate both humoral immune and cellular immune responses and elevate lymphocyte proliferation, thus eliciting a Th1-type immune response in a murine immunity and infection model. Stimulation of Raw 264.7 macrophages with PotD validated that Toll-like receptor 4, rather than 2, participated in the positive transcription and expression of pro-inflammatory cytokines IL–1β, IL–6, and TNF–α using qPCR and ELISA. Blocking signal-regulated JNK–MAPK and RelA(p65) pathways significantly decreased PotD-induced pro-inflammatory cytokine production. Overall, we conclude that vaccination of PotD could induce both humoral and cellular immune responses and provide immunoprotection against H. parasuis challenge. The data also suggest that Glaesserella PotD is a novel pro-inflammatory mediator and induces TLR4-dependent pro-inflammatory activity in Raw 264.7 macrophages through JNK–MAPK and RelA(p65) pathways.