Haemophilus parasuis: new trends on diagnosis, epidemiology and control

Advanced Research in Porcine Reproductive and Respiratory Syndrome Virus Co-infection With Other Pathogens in Swine

The porcine reproductive and respiratory syndrome virus (PRRSV) is the pathogen causing epidemics of porcine reproductive and respiratory syndrome (PRRS), and is present in every major swine-farming country in the world. Previous studies have demonstrated that PRRSV infection leads to a range of consequences, such as persistent infection, secondary infection, and co-infection, and is common among pigs in the field. In recent years, coinfection of PRRSV and other porcine pathogens has occurred often, making it more difficult to define and diagnose PRRSV-related diseases. The study of coinfections may be extremely suitable for the current prevention and control in the field. However, there is a limited understanding of coinfection. Therefore, in this review, we have focused on the epidemiology of PRRSV coinfection with other pathogens in swine, both in vivo and in vitro.

Deletion of the crp gene affects the virulence and the activation of the NF-κB and MAPK signaling pathways in PK-15 and iPAM cells derived from G. parasuis serovar 5

Glaesserella parasuis can cause serious systemic disease (Glasser's disease) that is characterized by fibrinous polyserositis, polyarthritis and meningitis. cAMP receptor protein (CRP) is among the well studied global regulator proteins which could modulate the virulence of many pathogenic bacteria. Our previous study showed that the crp gene was involved in the regulation of growth rate, biofilm formation, stress tolerance, serum resistance, and iron utilization in G. parasuis. However, whether the crp gene could regulate the virulence of G. parasuis has not been analyzed previously. In this study, it was observed that the crp gene in G. parasuis serovar 5 (HPS5) was involved in regulating the adhesion and invasion abilities on iPAM cells, and the mRNA expression of various virulence-related factors. It also possessed the ability to induce the mRNA expression of pro-inflammatory cytokines (IL-1α, IL-1β, IL-6, IL-8 and TNF-α), promoted the activation of the nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways in porcine kidney epithelial (PK-15) and immortalized swine pulmonary alveolar macrophage (iPAM) cells, and contributed to the pathogenicity and organs colonization in mice. As compared with the wild type, both the expression of virulence-related factors in the crp mutant strain and its ability to induce the mRNA expression of pro-inflammatory cytokines, as well as the expression of phospho-p65 and phospho-p38 in PK-15 and iPAM cells was reduced significantly. Furthermore, it also found that the virulence of crp mutant was significantly reduced as compared with the wild type. However, the abilities of adherence and invasion on iPAM cell of Δcrp strain was noted to be significantly enhanced as compared with the wild type. These results suggested that the crp gene deletion could effectively attenuate the virulence of G. parasuis, and crp gene may act as an important potential target for the formulation of a novel vaccine against G. parasuis.

Rhein Derivatives, A Promising Pivot?

Rhein, an anthraquinone derivative, has been employed widely, especially for the treatment of intractable diseases like diabetic nephropathy, arthritis, and cancer in a unique action mechanism. In the last decades, considerable efforts have been made in structural modification of rhein. This paper reviewed patents on pharmacological activity and therapeutic application of rhein and its derivatives from 1978 to 2018. Particularly, an analysis of patents was made, with the top 10 most valuable patents presented, and the interpretation of the legal status of patents was given. Given the properties of superior pharmacological activity, rich resources, cheap price, low toxicity, and mature extraction process, it is believed that an in-depth investigation on rhein and its derivatives is worth trying.

Characterization and protective activity of monoclonal antibodies directed against Fe (3+) ABC transporter substrate-binding protein of Glaesserella parasuis

Glässer's disease is caused by the agent Glaesserella parasuis and is difficult to prevent and control. Candidate screening for subunit vaccines contributes to the prevention of this disease. Therefore, in this study, the inactivated G. parasuis reference serovar 5 strain (G. parasuis-5) was used to generate specific monoclonal antibodies (mAbs) to screen subunit vaccine candidates. Six mAbs (1A12, 3E3, 4C6, 2D1, 3E6, and 4B2) were screened, and they all reacted with the G. parasuis serovar 5 strain according to laser confocal microscopy and flow cytometry (FCM). Indirect enzyme-linked immunosorbent assay (ELISA) showed that one mAb 2D1, can react with all 15 reference serovars of G. parasuis. Protein mass spectrometry and Western blot analysis demonstrated that mAb 2D1 specifically reacts with Fe (3+) ABC transporter substrate-binding protein. A complement killing assay found that the colony numbers of bacteria were significantly reduced in the G. parasuis-5 group incubated with mAb 2D1 (p < 0.01) in comparison with the control group. Opsonophagocytic assays demonstrated that mAb 2D1 significantly enhanced the phagocytosis of 3D4/21 cells by G. parasuis (p < 0.05). RAW264.7 cells with stronger phagocytic ability were also used for the opsonophagocytic assay, and the difference was highly significant (p < 0.01). Passive immunization of mice revealed that mAb 2D1 can eliminate the bacteria in the blood and provide protection against G. parasuis-5. Our study found one mAb that can be used to prevent and control G. parasuis infection in vivo and in vitro, which may suggest that Fe (3+) ABC transporter substrate-binding protein is an immunodominant antigen and a promising candidate for subunit vaccine development.

Exploration of Clinical Breakpoint of Danofloxacin for Glaesserella parasuis in Plasma and in PELF

Background: In order to establish the clinical breakpoint (CBP) of danofloxacin against G. parasuis, three cutoff values, including epidemiological cutoff value (ECV), pharmacokinetic-pharmacodynamic (PK-PD) cutoff value (CO_PD) and clinical cutoff value (CO_CL), were obtained in the present study. Methods: The ECV was calculated using ECOFFinder base on the MIC distribution of danfloxacin against 347 G. parasuis collected from disease pigs. The CO_PD was established based on in vivo and ex vivo PK-PD modeling of danofloxacin both in plasma and pulmonary epithelial lining fluid (PELF) using Hill formula and Monte Carlo analysis. The CO_CL was established based on the relationship between the possibility of cure (POC) and MIC in the clinical trials using the "WindoW" approach, nonlinear regression and CART analysis. Results: The MIC₅₀ and MIC₉₀ of danofloxacin against 347 G. parasuis were 2 μg/mL and 8 μg/mL, respectively. The ECV value was set to 8 μg/mL using ECOFFinder. Concentration-time curves of danofloxacin were fitted with a two-compartment PK model. The PK parameters of the maximum concentration (C_max) and area under concentration-time curves (AUC) in PELF were 3.67 ± 0.25 μg/mL and 24.28 ± 2.70 h·μg/mL, higher than those in plasma (0.67 ± 0.01 μg/mL and 4.47 ± 0.51 h·μg/mL). The peak time (T_max) in plasma was 0.23 ± 0.07 h, shorter than that in PELF (1.61 ± 0.15 h). The CO_PD in plasma and PELF were 0.125 μg/mL and 0.5 μg/mL, respectively. The CO_CL calculated by WindoW approach, nonlinear regression and CART analysis were 0.125-4 μg/mL, 0.428 μg/mL and 0.56 μg/mL, respectively. The 0.5 μg/mL was selected as eligible CO_CL. The ECV is much higher than the CO_PD and CO_CL, and the clinical breakpoint based on data in plasma was largely different from that of PELF. Conclusions: Our study firstly established three cutoff values of danofloxacin against G. parasuis. It suggested that non-wild-type danofloxacin-resistant G. parasuis may lead to ineffective treatment by danofloxacin.

Comparison of the Glaesserella parasuis Virulence in Mice and Piglets

In this study, we compared the virulence of the most common serovars of Glaesserella parasuis in China, serovars 4, 5, 12, and 13 (36 strains in total) in BALB/c mice and piglets. In mice, the median lethal doses (LD₅₀s) of the four serovars were roughly 9.80 × 10⁷–4.60 × 10⁹ CFU, 2.10 × 10⁸–8.85 × 10⁹ CFU, 4.81 × 10⁷–7.01 × 10⁹ CFU, and 1.75 × 10⁸–8.45 × 10⁸ CFU, respectively. Serovar 13 showed the strongest virulence, followed by serovar 4, serovar 12, and serovar 5, but a significant difference in virulence was only observed between serovars 5 and 13. The virulence of strains of the same serovars differed significantly in piglets. Virulent and attenuated strains were present in all serovars, but serovar 5 was the most virulent in piglets, followed by serovars 13, 4, and 12. A significant difference in virulence was observed between serovars 5 and 4 and between serovars 5 and 12. However, the virulence of serovars 5 and 13 did not differ significantly. This comprehensive analysis of G. parasuis virulence in mice and piglets demonstrated that: (1) the order of virulence of the four domestic epidemic serovars (from strongest to weakest) in piglets was serovars 5, 13, 4, and 12; (2) both virulent and attenuated strains were present in all serovars, so virulence did not necessarily correlate with serovar; (3) Although G. parasuis was fatal in BALB/c mice, its virulence is inconsistent with that in piglets, indicating that BALB/c mice are inadequate as an alternative model of G. parasuis infection.

Inhibition of Haemophilus parasuis by berberine and proteomic studies of its mechanism of action

Haemophilus parasuis is the main agent of Glässer's disease, which causes substantial losses in pig production. However, the pathogenic mechanism and virulence factors of H. parasuis have not been fully determined. In this study, berberine is shown to have a good therapeutic effect in vivo against H. parasuis; the minimal inhibitory concentration (MIC) in vitro was 2 μg/mL. Berberine inhibited H. parasuis adhesion to and invasion of PK-15 pig kidney cells. Proteomics studies of H. parasuis after berberine treatment identified a total of 97 differentially-expressed proteins; 35 upregulated and 62 downregulated. Bioinformatics analysis showed that berberine may inhibit the growth of H. parasuis by affecting outer membrane proteins, transferrins, and energy metabolism. This study provides a basis for the development of new antibacterial agents.

Molecular Characterization of Multidrug-Resistant Yersinia enterocolitica From Foodborne Outbreaks in Sweden

The foodborne pathogen Yersinia enterocolitica causes gastrointestinal infections worldwide. In the spring of 2019, the Swedish Public Health Agency and Statens Serum Institut in Denmark independently identified an outbreak caused by Yersinia enterocolitica 4/O:3 that after sequence comparison turned out to be a cross-border outbreak. A trace-back investigation suggested shipments of fresh prewashed spinach from Italy as a common source for the outbreak. Here, we determined the genome sequences of five Y. enterocolitica clinical isolates during the Swedish outbreak using a combination of Illumina HiSeq short-read and Nanopore Technologies’ MinION long-read whole-genome sequencing. WGS results showed that all clinical strains have a fully assembled chromosome of approximately 4.6 Mbp in size and a 72-kbp virulence plasmid; one of the strains was carrying an additional 5.7-kbp plasmid, pYE-tet. All strains showed a high pathogen probability score (87.5%) with associated genes for virulence, all of which are closely related to an earlier clinical strain Y11 from Germany. In addition, we identified a chromosomally encoded multidrug-resistance cassette carrying resistance genes against chloramphenicol (catA1), streptomycin (aadA1), sulfonamides (sul1), and a mercury resistance module. This chromosomally encoded Tn2670 transposon has previously been reported associated with IncFII plasmids in Enterobacteriaceae: a Shigella flexneri clinical isolate from Japan in 1950s, a Klebsiella pneumoniae outbreak from Australia in 1997, and Salmonella enterica serovar Typhimurium. Interestingly, we identified an additional 5.7-kbp plasmid with tetB (encoding an ABC transporter), Rep, and its own ORI and ORIt sites, sharing high homology with small tetB-Rep plasmids from Pasteurellaceae. This is the first time that Tn2670 and Pasteurellaceae plasmids have been reported in Y. enterocolitica. Taken together, our study showed that the Swedish Y. enterocolitica outbreak strains acquired multi-antibiotic and metal-resistance genes through horizontal gene transfer, suggesting a potential reservoir of intraspecies dissemination of multidrug-resistance genes among foodborne pathogens. This study also highlights the concern of food-chain contamination of prewashed vegetables as a perpetual hazard against public health.

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.

Comparative Transcriptomic Analyses of Haemophilus parasuis Reveal Differently Expressed Genes among Strains with Different Virulence Degrees

Haemophilus parasuis is commonly found in the upper respiratory tract of the pigs. Some isolates of H. parasuis can lead to both pneumonia and Glässer's disease of pigs with severe clinical symptoms. The virulence-associated genes for the various degrees of virulence observed in H. parasuis remains poorly understood. In the present study, we identified the differentially expressed genes between YK1603 (non-virulent strain) and XM1602 (moderately virulent strain) or CY1201 (highly virulent strain) of H. parasuis using Illumina sequencing technique. In comparison to YK1603, a total of 195 genes were significantly changed in CY1201, of which 71 genes were up-regulated and 124 genes were down-regulated, whereas 705 genes were significantly changed in XM1602, of which 415 genes were up-regulated and 290 genes were down-regulated. The enriched analysis of Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways on the differentially expressed genes showed that both enriched main GO terms and KEGG pathways appear to be different between the two kinds of comparision: CY1201 versus YK1603, and XM1602 versus YK1603. Based on real-time PCR technique, on the whole, it was confirmed that the expression of ten genes: lpxL, tbpB, kdtA, waaQ, oapA, napA, ptsH, mmsA, lpxM, and lpxB were agreement with the findings in Illumina sequencing analysis. These identified genes might participate in the regulation of a wide range of biological process involved in virulence of H. parasuis, such as phosphotransferase system and ABC transporters. Our results from this study provide a new way to gain insight into the virulent mechanisms of H. parasuis.

Ct value-based real time PCR serotyping of Glaesserella parasuis

Glaesserella parasuis is the causative agent of Glässer's disease in swine. Serotyping plays an essential role in prevalence investigations and in the development of vaccination strategies for the prevention of this disease. Molecular serotyping based on variation within the capsule loci of the 15 serovars is more accurate and efficient than traditional serological serotyping. To reduce the running time and facilitate ease of data interpretation, we developed a simple and rapid cycle threshold (Ct) value-based real time PCR (qPCR) method for the identification and serotyping of G. parasuis. The qPCR method distinguished between all 15 serovar reference strains of G. parasuis with efficiency values ranging between 85.5 % and 110.4 % and, R² values > 0.98. The qPCR serotyping was evaluated using 83 clinical isolates with 43 of the isolates having been previously assigned to a serovar by the gel immuno-diffusion (GID) assay and 40 non-typeable isolates. The qPCR results of 41/43 (95.3 %) isolates were concordant with the GID assay except two isolates of serovar 12 were assigned to serovar 5. In addition, the qPCR serotyping assigned a serovar to each of the 40 non-typeable isolates. Of the 83 isolates tested to assign a serovar, a concordance rate of 98.8 % (82/83) was determined between the qPCR and the previously reported multiplex PCR of Howell et al. (2015) (including those that were either serovars 5 or 12). Despite the inability to differentiate between serovars 5 and 12, the Ct value-based qPCR serotyping represents an attractive alternative to current molecular serotyping method for G. parasuis and could be used for both epidemiological monitoring and the guidance of vaccination programs.

Evidence for Establishing the Clinical Breakpoint of Cefquinome against Haemophilus Parasuis in China

Haemophilus parasuis can cause high morbidity and mortality in swine. Cefquinome possesses excellent antibacterial activity against pathogens causing diseases of the respiratory tract. This study aimed to establish the clinical breakpoint (CBP) of cefquinome against H. parasuis and to monitor the resistance change. Referring to the minimum inhibitory concentration (MIC) distribution of cefquinome against 131 H. parasuis isolates, the MIC₅₀ and MIC₉₀ were determined to be 0.125 and 1 μg/mL, respectively. And the epidemiological cutoff (ECOFF) value was 1 μg/mL. HPS42 was selected as a representative strain for the pharmacodynamic (PD) experiment, pharmacokinetic (PK) experiment and clinical experiments. The PK/PD index values, area under concentration-time curve (AUC)/MIC, of the bacteriostatic, bactericidal, and bacterial elimination effects were 23, 41, and 51 h, respectively. The PK/PD cutoff was calculated as 0.125 μg/mL by Monte Carlo simulation (MCS), and the clinical cutoff was 0.25−4 μg/mL by WindoW. Combing these three values, the CBP of cefquinome against H. parasuis was found to be 1 μg/mL. In conclusion, this was the first study to integrate various cutoffs to establish the CBP in the laboratory. It is helpful to distinguish wild type H. parasuis and reduce the probability of treatment failure.

ICEHpsaHPS7, a Novel Multiple Drug Resistance Integrative Conjugative Element in Glaesserella parasuis

Integrative conjugative elements (ICEs) are a kind of novel self-transmissible mobile genetic element. In this study, a novel ICE was identified in Glaesserella (Haemophilus) parasuis We confirmed that it could mediate the migration of antimicrobial resistance genes in G. parasuis and found that there may have been a transferring potential between different serovar strains of G. parasuis These findings demonstrate that the ICE is crucial to the horizontal transfer of antimicrobial resistance among G. parasuis strains.

Glässer’s disease in swine from Northeastern Brazil

ABSTRACT: Glässer’s disease is an important infectious disorder of swine caused by Haemophilus parasuis. Although well recognized in most regions of Brazil, outbreaks of Glässer’s disease have not been described in Northeastern region. For this reason, three municipalities of the Pernambuco State were visited in order to identify histories of high mortality in growing and finishing pigs. The main clinical signs consisted of dry cough, apathy, fever, anorexia, paresis, muscle tremors, motor incoordination, seizures leading to high mortality rates. Nine pigs were necropsied, and fragments of the nervous system, organs of the abdominal and thoracic cavities were collected for histological analysis. In addition, lung and brain fragments were used for DNA extraction and molecular testing by real-time Polymerase Chain Reaction (PCR). Grossly, the main lesions consisted of petechial hemorrhages or ecchymosis on the skin of the face, abdomen, forelimbs, and hind limbs. The main severe lesions consisted of hydropericardium, hemopericardium, fibrinous pericarditis and pleuropneumonia. Microscopically, pericarditis, epicarditis and subepicardial myocarditis, followed by a moderate to severe multifocal pleuropneumonia, fibrinosuppurative and necrotizing were the most frequent lesions observed. Real-time PCR amplified H. parasuis infB gene in all samples analyzed, confirming the presence of this etiologic agent.

The effects of baicalin on piglets challenged with Glaesserella parasuis

Glaesserella parasuis (G. parasuis) causes porcine vascular inflammation and damage. Baicalin is reported to have antioxidant and anti-inflammatory functions. However, whether baicalin protects piglets against G. parasuis challenge and the potential protective mechanism have not been investigated. Therefore, in this study, we comprehensively examined the protective efficacy of baicalin in piglets challenged with G. parasuis and the possible protective mechanism. Our results show that baicalin attenuated the release of the inflammation-related cytokines interleukin (IL) 1β, IL6, IL8, IL10, and tumour necrosis factor α (TNF-α) and reduced high mobility group box 1 (HMGB1) production and cell apoptosis in piglets infected with G. parasuis. Baicalin also inhibited the activation of the mitogen-activated protein kinase (MAPK) signalling pathway and protected piglets against G. parasuis challenge. Taken together, our data suggest that baicalin could protect piglets from G. parasuis by reducing HMGB1 release, attenuating cell apoptosis, and inhibiting MAPK signalling activation, thereby alleviating the inflammatory response induced by the bacteria. Our results suggest that baicalin has utility as a novel therapeutic drug to control G. parasuis infection.

Molecular Characterization of a Novel Integrative Conjugative Element ICEHpa1 in Haemophilus parasuis

ICEHpa1 was identified in the genome of a serovar 8 Haemophilus parasuis ST288 isolate YHP170504 from a case of swine lower respiratory tract infection. The aim of the present study was to characterize the integrative conjugative element ICEHpa1 and its multiresistance region. Susceptibility testing was determined by broth microdilution and the complete ICEHpa1 was identified by WGS analysis. The full sequence of ICEHpa1 was analyzed with bioinformatic tools. The presence of ICEHpa1, its circular intermediate and integration site were confirmed by PCR and sequence analysis. Transfer of ICEHpa1 was confirmed by conjugation. ICEHpa1 has a size of 68,922 bp with 37.42% GC content and harbors 81 genes responsible for replication and stabilization, transfer, integration, and accessory functions, as well as seven different resistance genes [bla _{Rob- 3}, tet(B), aphA1, strA, strB, aac(6)'-Ie-aph(2')-Ia, and sul2]. Conjugation experiments showed that ICEHpa1 could be transferred to H. parasuis V43 with frequencies of 6.1 × 10^-6. This is the first time a multidrug-resistance ICE has been reported in H. parasuis. Seven different resistance genes were located on a novel integrative conjugative element ICEHpa1, which suggests that the ICEHpa1 is capable of acquiring foreign genes and serving as a carrier for various resistance genes.

The Glaesserella parasuis phosphoglucomutase is partially required for lipooligosaccharide synthesis

Lipooligosaccharides (LOSs) are virulence determinants of Glaesserella parasuis, a pathogen of the respiratory tract of pigs. We previously reported that disruption of the galU or galE gene in G. parasuis results in increased sensitivity to porcine serum, indicating that the galactose catabolism pathway is required for polysaccharide formation in G. parasuis. Here, we evaluated the role of the HAPS_0849 gene in LOS synthesis. The G. parasuis SC096 HAPS_0849 mutant produced a highly truncated LOS molecule, although a small fraction of intact LOS was still observed, and this mutant was found to be more sensitive to serum than the parental strain. HAPS_0849 was overexpressed and purified for biochemical assays, and this protein exhibited phosphoglucomutase (PGM) activity. Heterologous expression of a pgm gene from Escherichia coli in the HAPS_0849 mutant led to restoration of the wild-type LOS glycoform, further demonstrating the PGM function of HAPS_0849 in G. parasuis. The autoagglutination and biofilm formation ability of this strain were also investigated. Disruption of HAPS_0849 led to an increased tendency to autoagglutinate and form more biofilms, and these enhanced phenotypes were observed in the absence of glucose. In addition, LOSs from HAPS_0849, galU and lgtB mutants had similar truncated glycoforms, while LOSs from the galE and lex-1 mutants exhibited another type of defective LOS pattern. These findings imply that HAPS_0849 may function upstream of GalU in the generation of glucose 1-phosphate. In conclusion, our results preliminarily described the functions of HAPS_0849 in G. parasuis, and this gene was partially required for LOS synthesis.

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.

Development of a recombinase polymerase amplification assay for rapid detection of Haemophilus parasuis in tissue samples

Haemophilus parasuis is the etiological agent of Glässer's disease in swine, which associates with severe economic losses in the swine industry worldwide. A real‐time recombinase polymerase amplification assay (real‐time RPA) was developed for direct and rapid detection of H. parasuis basing on the translation‐initiation factor IF2 (infB) gene. The assay was performed successfully at 39°C for 20 min in Genie III, which is portable and chargeable by battery. The developed assay was highly specific for H. parasuis, and the limit of detection of the assay was 6.0 × 10³ fg of H. parasuis genomic DNA, which was the same as that of a real‐time PCR developed previously. The assay was further evaluated on 68 pig tissue samples, and 18 (26.5%), 20 (29.4%), and 8 (11.8%) samples were positive for H. parasuis by the real‐time RPA, real‐time PCR and bacterial isolation, respectively. With the bacteria isolation as the reference method, the real‐time RPA showed a diagnostic specificity of 83.33% and a diagnostic sensitivity of 100%. The above data demonstrated the well‐potentiality and usefulness of the developed real‐time RPA assay in reliable diagnosis of swine Glässer's disease, especially in resource limited settings.

Identification of a multiple drug-resistance gene island in the Haemophilus parasuis chromosome

OBJECTIVES

The aim of this study was to determine the mechanisms and molecular characterisation of one strain (HPS412) of Haemophilus parasuis, which exhibited high MICs of antimicrobial susceptibility.

METHODS

A total of 113 H. parasuis strains isolated from pigs suffering from polyserositis, pneumonia or meningitis in China and screened them for antimicrobial susceptibility. Susceptibility testing of the minimal inhibitory concentrations (MIC) was determined in fastidious medium consisting of tryptone soya broth (TSB) containing 5% bovine serum and 10μg/mL NAD in 96-well microtiter plates. The genomic DNA was completely sequenced by combining PacBio RS II and Illumina HiSeq 4000 platforms. Gene prediction was performed using Glimmer v.3.02 with Hidden Markov models.

RESULTS

One strain (HPS412) exhibited high MICs of sulfamethoxazole (256μg/mL), tetracycline (128μg/mL), streptomycin (128μg/mL), gentamicin (128μg/mL), amoxicillin (128μg/mL), chloramphenicol (64μg/mL), penicillin (64μg/mL) and cefaclor (64μg/mL). Sequence analysis showed that numerous drug-resistance genes including tet(B), bla_ROB-1, sul2, catIII, aph(3″)-Ib, aph(6)-Id and aph(3')-Ia were present in a chromosomal gene island as adjacent duplicate copies and the rep-orf3-bla_ROB-1 structure most likely had a direct plasmid origin. The tet(B) and bla_ROB-1 were flanked on one or both by ISApl1 elements.

CONCLUSIONS

The acquisition of bla_ROB-1 and the other antibiotic resistance genes was related to the presence of ISApl1. ISApl1 plays important roles in the horizontal transmission of antibiotic resistance genes.

Current Swine Respiratory Diseases Morphology in Intensive Swine Production in Serbia

Swine respiratory diseases represent one of the most frequent health issues in pig production worldwide. Despite the great progress that has been made in the field of diagnostics, control and prophylaxis, respiratory diseases still remain the most challenging health problem in modern commercial pig production. The list of infectious agents that cause respiratory diseases in swine is extensive and includes both, bacterial and viral pathogens. In Serbia, more than fifteen years after the introduction of modern vaccines, the list of bacterial pathogens related to swine respiratory infections still include Mycoplasma hyopneumoniae, Actinobacillus pleuropneumoniae, Haemophilus parasuis and Pasteurella multocida. On the other hand, most commonly involved viral pathogens are Porcine Reproductive and Respiratory Syndrome Virus, Swine influenza virus, Porcine circovirus type 2 and Pseudorabies virus. The morphological features of pneumonia where several agents are involved, depend on the predominant etiological agent. Expanding knowledge of the main pathogens associated with swine respiratory diseases and the effects of their interactions on the disease outcome is important for further investigations of lung diseases and implementation of control strategies in commercial pig populations in Serbia. This review discusses the latest findings on swine respiratory disease and current trends in Serbian pig production.

COX-2 mediated crosstalk between Wnt/β-catenin and the NF-κB signaling pathway during inflammatory responses induced by Haemophilus parasuis in PK-15 and NPTr cells

Haemophilus parasuis infection causes typical acute systemic inflammation in pigs, is characterized by fibrinous polyserositis inflammation, and results in great economic losses to the swine industry worldwide. However, the molecular details of how the host modulates the acute inflammatory response induced by H. parasuis are largely unknown. In previous studies, we found that H. parasuis high-virulence strain SH0165 infection induced the activation of both Wnt/β-catenin and NF-κB signaling in PK-15 and NPTr cells. In this study, we found that the activation of NF-κB, a central hub in inflammatory signaling, was impeded by the Wnt/β-catenin pathway during H. parasuis infection. In contrast, blocking NF-κB activity had no effect on the Wnt/β-catenin pathway during H. parasuis infection. Furthermore, we found that the inhibitory effect of β-catenin on NF-κB activity was mediated by its target gene, pig cyclooxygenase-2 (COX-2). Therefore, we demonstrated that H. parasuis infection activates the canonical Wnt/β-catenin signaling pathway, which leads to decreased NF-κB activity, reducing the acute inflammatory response in pigs. Additionally, the data provide a possible perspective for understanding the anti-inflammatory role of Wnt/β-catenin in pigs during bacterial infection.

Infectious diseases dynamics in growing/finishing pigs in Southern Brazil (2005-2016)

ABSTRACT: This study aimed to determine the frequency and distribution of infectious diseases diagnosed through necropsy examination and histopathological analysis in growing/finishing pigs along 12 years (2005-2016) in Southern Brazil. We evaluated 1906 anatomopathological exams of pigs at growing/finishing phases, of which the infectious diseases corresponded to 75.6% of the cases (1,441/1,906). Porcine circovirus type 2 (PCV2) infections were the most frequent, accounting for 51.3% of the cases (739/1,441) with a higher frequency from 2005 to 2007, characterizing an epidemic distribution, with a gradual decline after 2008. Infectious diseases affecting the respiratory system were the second major cause with 30.1% of the cases. Among these, necrotizing bronchiolitis caused by swine Influenza (15.1%, 218/1,441) and bacterial pneumonia (15%, 216/1,441) were the main conditions. Influenza was mostly diagnosed from 2010 to 2013, accounting for 43.1% (167/387) of the cases. After this period, both respiratory infectious diseases were endemic. Digestive system infectious diseases accounted for 10.5% of the diagnoses (151/1,441), with the following main conditions: Salmonella spp. enterocolitis (43.7%, 66/151), Lawsonia spp. proliferative enteropathy (41.7%, 63/151), and Brachyspira spp. colitis (14.6%, 22/151). The latter had a higher incidence from 2012 to 2014 with all cases detected in this period. Polyserositis and bacterial meningitis represented, respectively, 5.8% (84/1,441) and 2.3% (33/1,441) of the cases diagnosed, with a constant endemic character.

Phylogenomic analysis of Haemophilus parasuis and proposed reclassification to Glaesserella parasuis, gen. nov., comb. nov

The Gram-negative bacterium Haemophilus parasuis is the etiologic agent of Glässer's disease in pigs, and causes significant economic losses to the swine industry. This bacterium has been classified as a member of the family Pasteurellaceae in the genus Haemophilus, but phylogenetic relatedness has not been adequately examined to support this genus classification. Phenotypically, all 38 strains of H. parasuis tested were positive for catalase activity, oxidase activity, V-factor requirement, and acid formation from maltose and d-galactose without gas. All strains were negative for X-factor requirement, formation of indole from tryptophan, urease, l-arabinose, and α-glucosidase activity. To determine whether H. parasuis belongs to one of the current Pasteurellaceae genera 40 H. parasuis genomes, plus those of representative Pasteurellaceae, were subjected to phylogenetic analysis of concatenated, multi-protein alignments. Sequence variation at 16S rRNA and rpoB loci allowed the 15 reference serovars of H. parasuis to be integrated into the whole-genome tree. The phylogenetic analysis showed H. parasuis to be a distinct and tight clade whose sister taxon is the genus Bibersteinia. Within H. parasuis two clades were identified with individual serovars distributed between the two. As a result, H. parasuis was confirmed as a member of the family Pasteurellaceae, but was distinct from other genera in this family. Therefore, we propose the name Glaesserella parasuis, gen. nov., comb. nov. for bacterial strains currently classified as H. parasuis. The reference strain of this species is ATCC 19417 (1374)^T, NCTC 4557^T, DSM 21448^T, CCUG 3712^T.

Variations in association of nasal microbiota with virulent and non-virulent strains of Glaesserella (Haemophilus) parasuis in weaning piglets

Glaesserella (formerly Haemophilus) parasuis causes Glässer’s disease, which results in high economic loss in the swine industry. To understand the polymicrobial interactions of G. parasuis and the nasal microbiota, the statistical association patterns of nasal colonizing bacteria with virulent and non-virulent strains of G. parasuis were studied accounting for the farm management practices as potential risk factors for the occurrence of Glässer’s disease. The nasal microbiota from 51 weaned-piglets from four farms with Glässer’s disease and three farms with no respiratory diseases was previously characterized and included in this study. The presence of virulent and/or non-virulent G. parasuis strains in the nasal cavities was determined in order to establish the potential association with other members of the nasal microbiota. Multivariate logistic and linear regression models were performed among the various members of nasal microbiota and G. parasuis. The multi-site production system and disease presence in the farm were both significantly associated with the presence of G. parasuis virulent strains in the nose of the piglets. Differential bacterial associations were observed with virulent or non-virulent G. parasuis. Chitinophagaceae, Corynebacteriaceae and Corynebacterium were positively associated with the virulent G. parasuis strains, while Enterobacteriaceae, Peptostreptococcaceae, Clostridium XI, and Escherichia/Shigella were negatively associated with virulent G. parasuis. On the other hand, Flavobacteriaceae, Planobacterium, and Phascolarctobacterium were positively associated with the non-virulent G. parasuis strains, while Rikenellaceae, Enterococcaceae, Odoribacter, and Corynebacterium were negatively associated with non-virulent G. parasuis. In conclusion, the nasal microbiota communities showed variations in the association with the G. parasuis strains type.

Development and application of an antibody detection ELISA for Haemophilus parasuis based on a monomeric autotransporter passenger domain

Background

Haemophilus parasuis is a commensal pathogen in the swine upper respiratory tract and causes Glässer’s disease. Surveillance, screening for infection, and vaccination response of H. parasuis is hindered by the lack of a rapid antibody detection method.

Results

In the present study, a monomeric autotransporter was identified as a novel antigen for developing an indirect ELISA. The autotransporter passenger domain (Apd) was expressed, purified, and demonstrated to be specific in ELISA and western blotting. Mouse antiserum of recombinant Apd (rApd) recognized native Apd in the 15 serotype reference strains and five non-typeable isolate stains, but showed no reaction with seven other bacterial pathogens. The rApd ELISA was optimized and validated using 67 serum samples with known background, including 27 positive sera from experimentally infected and vaccinated pigs along with 40 negative sera that had been screened with H. parasuis whole cell ELISA from clinically healthy herds. The rApd ELISA provided positive and negative percent agreements of 96.4 and 94.9%, respectively, and an AUC value of 0.961, indicating that the assay produced accurate results.

Conclusion

Apd was a universal antigen component among 15 serotype and non-typeable strains of H. parasuis and was also specific to this pathogen. The rApd ELISA could detect antibodies elicited by H. parasuis infection and vaccination, thereby exhibiting the potential to be applied for Glässer’s disease diagnosis, H. parasuis vaccination evaluation, and large-scale serological surveillance.

Porcine Alveolar Macrophages' Nitric Oxide Synthase-Mediated Generation of Nitric Oxide Exerts Important Defensive Effects against Glaesserella parasuis Infection

Glaesserella parasuis is a habitual bacterium of pigs' upper respiratory tracts. Its infection initiates with the invasion and colonization of the lower respiratory tracts of pigs, and develops as the bacteria survive host pulmonary defenses and clearance by alveolar macrophages. Alveolar macrophage-derived nitric oxide (NO) is recognized as an important mediator that exerts antimicrobial activity as well as immunomodulatory effects. In this study, we investigated the effects and the signaling pathway of NO generation in porcine alveolar macrophages 3D4/21 during G. parasuis infection. We demonstrated a time and dose-dependent generation of NO in 3D4/21 cells by G. parasuis, and showed that NO production required bacterial viability and nitric oxide synthase 2 upregulation, which was largely contributed by G. parasuis-induced nuclear factor-κB signaling's activation. Moreover, the porcine alveolar macrophage-derived NO exhibited prominent bacteriostatic effects against G. parasuis and positive host immunomodulation effects by inducing the production of cytokines and chemokines during infection. G. parasuis in turn, selectively upregulated several nitrate reductase genes to better survive this NO stress, revealing a battle of wits during the bacteria-host interactions. To our knowledge, this is the first direct demonstration of NO production and its anti-infection effects in alveolar macrophages with G. parasuis infection.

Rapid and simple detection of Glaesserella parasuis in synovial fluid by recombinase polymerase amplification and lateral flow strip

Background

Glaesserella parasuis (G. parasuis) is an influential pathogen of the pig, which induces high morbidity and mortality in naive pig populations in the pig industry. Accurate and rapid detection of the agent is important for disease control. In this study, a simple recombinase polymerase amplification (RPA) with a Lateral flow (LF) strip (RPA-LF-GPS) was developed to detect G. parasuis.

Results

The RPA-LF-GPS can specifically detect G. parasuis a limit of 100 CFU from other common related pathogens causing arthritis in the pig. The RPA-LF-GPS assay can use boiled synovial fluid samples as a template with the same sensitivity as other DNA extraction methods. In the detection of clinic positive synovial fluid sample, RPA-LF-GPS is equally sensitive (98.1%) compared with that of PCR (90.4%) (P > 0.05). The whole procedure of the RPA-LF-GPS assay could be finished in 1 hour without professional equipment.

Conclusions

RPA-LF-GPS assay is a rapid and simple method for point-of-care diagnostic testing for G. parasuis infection.

PK/PD modeling of Ceftiofur Sodium against Haemophilus parasuis infection in pigs

BACKGROUND

Ceftiofur Sodium is widely used in China. Our aim was to determine Ceftiofur Sodium activity and optimize dosing regimens against the pathogen Haemophilus parasuis using an in vitro and ex vivo pharmacokinetics/pharmacodynamics modeling approach. By adopting these strategies, we wanted to extend the effective life of Ceftiofur Sodium in reduce drug-resistance in pigs.

RESULTS

We established an H. parasuis infection model in pigs, and assessed the pharmacokinetics of Ceftiofur Sodium in both healthy and infected animals. After Ceftiofur Sodium (10 mg/kg, i.m.) administration to healthy and H. parasuis-infected pigs, plasma based desfuroylceftiofur (a metabolite of Ceftiofur Sodium) was measured by High Performance Liquid Chromatography. The pharmacokinetics of Ceftiofur Sodium (desfuroylceftiofur) was consistent with a two-compartment open model, with first-order absorption. We observed no significant differences (P > 0.05) in pharmacokinetic parameters between healthy and infected pigs. Pharmacodynamics data showed that Ceftiofur Sodium was highly inhibitory against H. parasuis, with MIC, MBC, and MPC values of 0.003125, 0.0125 and 0.032 μg/mL, respectively. Desfuroylceftiofur in plasma also had strong bactericidal activity. Almost all H. parasuis cultured in plasma medium of Ceftiofur Sodium-inoculated healthy pigs, at each time point, were killed within 24 h. A weaker antibacterial activity was measured in infected-pig plasma medium at 18, 24, 36, and 48 h, after Ceftiofur Sodium inoculation. Pharmacokinetic parameters were combined with ex vivo pharmacodynamic parameters, and the bacteriostatic effect (36.006 h), bactericidal effect (71.637 h) and clearance (90.619 h) within 24 h, were determined using the Hill equation. Dose-calculation equations revealed the optimal dose of Ceftiofur Sodium to be 0.599-1.507 mg/kg.

CONCLUSIONS

There were no significant differences in Ceftiofur Sodium pharmacokinetic parameters between healthy and infected pigs, although pharmacokinetics/pharmacodynamics fitting curves showed obviously differences. The optimal dose of Ceftiofur Sodium was lower than recommended (3 mg/kg), which may provide improved treatments for Glässers disease, with lower drug-resistance possibility.

Construction of targeted and integrative promoter-reporter plasmids pDK-K and pDK-G to measure gene expression activity in Haemophilus parasuis

Haemophilus parasuis (H. parasuis) is rather difficult to manipulate genetically due to the diversity of restriction-modification systems and other mechanisms harbored by various isolates. This prevents exogenous plasmids from replicating in this species and hinders research efforts focused on transcriptional regulators in this bacterium. In this study, we generated a convenient promoter reporter system based on gene knock-in method using natural transformation in H. parasuis. Gene knock-in has proven useful as a powerful tool facilitating identification and studying the transcription activities of regulators under a variety of conditions that favor gene transcription or expression from an incorporated promoter. The vectors, pDK-K and pDK-G, carrying promoterless reporter lacZ gene and two homologous sequences flanking a knock-in site, may have some advantages over the extensively used plasmid-bearing reporter system in other bacteria in stability and ease of genetic manipulation in H. parasuis. The knock-in site was positioned at a site occupied by flanking genes that were both hypothetical and had the same transcription orientation, thus the expression of the reversely cloned promoter-lacZ fusion wouldn't be affected by the upstream promoter on the chromosome. The expression activity of lacZ gene under the transcriptional activation of a 300 bp promoter-proximal segment of cyaA, crp or comA genes in H. parasuis was separately validated using X-gal and o-nitrophenyl-β-d-galactoside(ONPG) as substrates. The derivatives harboring promoter-lacZ fusion segments showed significantly higher β-galactosidase activity levels than the promoterlessones both in TSB++ broth and on TSA++ plate as screened either by X-gal method or the standard Miller method. We also used pDK vector to further certify that the cyaA promoter is inducible and whose transcriptional levels were in correlation with the growth kinetics of the bacteria in TSB++. With this system, gene knock-in method based on natural transformation in H. parasuis proved to be useful in identifying transcriptional regulation of a certain promoter.

Molecular serotyping of clinical strains of Haemophilus (Glaesserella) parasuis brings new insights regarding Glässer's disease outbreaks in Brazil

Glässer’s disease (GD) is an important infectious disease of swine caused by Haemophilus (Glaesserella) parasuis. Vaccination with inactivated whole cell vaccines is the major approach for prevention of H. parasuis infection worldwide, but the immunity induced is predominantly against the specific polysaccharide capsule. As a consequence, the available vaccines may not induce adequate protection against the field strains, when the capsules present in the vaccine strains are different from those in strains isolated from the farms. Therefore, it is crucial to map H. parasuis serovars associated with regional outbreaks so that appropriate bacterin vaccines can be developed and distributed for prevention of infection. In this study, 459 H. parasuis field strains isolated from different Glässer’s disease outbreaks that occurred in 10 different Brazilian States were analyzed for serotype using PCR-based approaches. Surprisingly, non-typeable (NT) strains were the second most prevalent group of field strains and along with serovars 4, 5 and 1 comprised more than 70% of the isolates. A PCR-based approach designed to amplify the entire polysaccharide capsule locus revealed 9 different band patterns in the NT strains, and 75% of the NT strains belonged to three clusters, suggesting that a number of new serovars are responsible for a substantial proportion of disease. These results indicate that commercially available vaccines in Brazil do not cover the most prevalent H. parasuis serovars associated with GD.

Genotypic analyses and virulence characterization of Glaesserella parasuis isolates from Taiwan

Background

Glaesserella (Haemophilus) parasuis (G. parasuis) causes severe economic losses in the swine industry. Multiple G. parasuis strains can exist in single animals. Typing techniques are required for identifying G. parasuis isolates. Different strains within a serovar display varying virulence. Enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) can assess the heterogeneity. The group 1 virulence-associated trimeric autotransporters (vtaA) gene is an indicator of virulence. The aim of this study was to characterize Taiwanese G. parasuis isolates via molecular serotyping, vtaA PCR and ERIC-PCR.

Methods

One hundred and forty-five strains were collected between November 2013 and March 2017 in Taiwan and further examined by molecular serotyping, vtaA PCR and ERIC-PCR.

Results

The dendrogram revealed heterogeneous genetic diversity within many clusters. Partial correlation between the ERIC-PCR clusters of different strains, serovars and lesion patterns was observed. Twelve herds (8.3%) infected with more than one strain. Group 1 vtaA positive rate reached 98.6%.

Discussion

This study showed the high genetic diversity of G. parasuis in Taiwan by a high discriminatory capability of ERIC-PCR. Group 1 vtaA commonly exists in G. parasuis isolates and may play important roles in the pathogenesis of Taiwanese G. parasuis isolates.

Haemophilus parasuis α-2,3-sialyltransferase-mediated lipooligosaccharide sialylation contributes to bacterial pathogenicity

Bacterial lipooligosaccharide (LOS) is an important virulence-associated factor, and its sialylation largely confers its ability to mediate cell adhesion, invasion, inflammation, and immune evasion. Here, we investigated the function of the Haemophilus parasuis α-2,3-sialyltransferase gene, lsgB, which determines the terminal sialylation of LOS, by generating a lsgB deletion mutant as well as a complementation strain. Our data indicate a direct effect of lsgB on LOS sialylation and reveal important roles of lsgB in promoting the pathogenicity of H. parasuis, including adhesion to and invasion of porcine cells in vitro, bacterial load and survival in vivo, as well as a contribution to serum resistance. These observations highlight the function of lsgB in mediating LOS sialylation and more importantly its role in H. parasuis infection. These findings provide a more profound understanding of the pathogenic mechanism of this disease-causing bacterium.

Autophagy Is a Defense Mechanism Inhibiting Invasion and Inflammation During High-Virulent Haemophilus parasuis Infection in PK-15 Cells

Bacterial infections activate autophagy and autophagy restricts pathogens such as Haemophilus parasuis through specific mechanisms. Autophagy is associated with the pathogenesis of H. parasuis. However, the mechanisms have not been clarified. Here, we monitored autophagy processes using confocal microscopy, western blot, and transmission electron microscopy (TEM) and found that H. parasuis SH0165 (high-virulent strain) but not HN0001 (non-virulent strain) infection enhanced autophagy flux. The AMPK/mTOR autophagy pathway was required for autophagy initiation and ATG5, Beclin-1, ATG7, and ATG16L1 emerged as important components in the generation of the autophagosome during H. parasuis infection. Moreover, autophagy induced by H. parasuis SH0165 turned to fight against invaded bacteria and inhibit inflammation. Then we further demonstrated that autophagy blocked the production of the cytokines IL-8, CCL4, and CCL5 induced by SH0165 infection through the inhibition of NF-κB, p38, and JNK MAPK signaling pathway. Therefore, our findings suggest that autophagy may act as a cellular defense mechanism in response to H. parasuis and provide a new way that autophagy protects the host against H. parasuis infection.

A novel nicotinamide adenine dinucleotide control strategy for increasing the cell density of Haemophilus parasuis

Haemophilus parasuis is the causative agent of Glässer's disease and is a major source of economic losses in the swine industry each year. To enhance the production of an inactivated vaccine against H. parasuis, the availability of nicotinamide adenine dinucleotide (NAD) must be carefully controlled to ensure a sufficiently high cell density of H. parasuis. In the present study, the real-time viable cell density of H. parasuis was calculated based on the capacitance of the culture. By assessing the relationship between capacitance and viable cell density/NAD concentration, the NAD supply rate could be adjusted in real time to maintain the NAD concentration at a set value based on the linear relationship between capacitance and NAD consumption. The linear relationship between cell density and addition of NAD indicated that 7.138 × 10⁹ NAD molecules were required to satisfy per cell growth. Five types of NAD supply strategy were used to maintain different NAD concentration for H. parasuis cultivation, and the results revealed that the highest viable cell density (8.57, OD₆₀₀ ) and cell count (1.57 × 10¹⁰ CFU/mL) were obtained with strategy III (NAD concentration maintained at 30 mg/L), which were 1.46- and 1.45- times more, respectively, than cultures with using NAD supply strategy I (NAD concentration maintained at 10 mg/L). An extremely high cell density of H. parasuis was achieved using this NAD supply strategy, and the results demonstrated a convenient and reliable method for determining the real-time viable cell density relative to NAD concentration. Moreover, this method provides a theoretical foundation and an efficient approach for high cell density cultivation of other auxotroph bacteria.

Investigation of Haemophilus parasuis from healthy pigs in China

Haemophilus parasuis is a common colonizer of the upper respiratory tract of swine and frequently causes disease, especially in weaner pigs. To date, limited epidemiological data was available for H. parasuis from healthy pigs, which might be carriers of potential pathogenic strains. In this study, from September 2016 to October 2017, we investigated the prevalence and characteristics of H. parasuis from healthy pigs in China. Totally, we obtained 244 isolates from 1675 nasal samples from 6 provinces. H. parasuis isolation was more successful in weaner pigs (22.6%, 192/849), followed by finisher pigs (9.3%, 43/463), and sows (2.5%, 9/363). The most prevalent serovars were 7 (20.1%, 49/244), followed by 3 (14.8%, 36/244), 2 (14.3%, 35/244), 11 (12.7%, 31/244), 5/12 (5.7%, 14/244) and 4 (2.5%, 6/244). Bimodal or multimodal distributions of MICs were observed for most of the tested drugs, which suggested the presence of non-wild type populations. It was noted that the MIC₉₀ values of tilmicosin (64 μg/ml) was relatively higher than that reported in previous studies. Our results suggest that: 1) potentially pathogenic serovars of H. parasuis are identified in healthy pigs, and 2) elevated MICs and presence of mechanisms of resistance not yet described for clinically important antimicrobial agents would increase the burden of disease caused by H. parasuis.

Characterization of serotypes and virulence genes of Haemophilus parasuis isolates from Central Vietnam

Haemophilus parasuis is a commensal Gram-negative bacterial pathogen in the upper respiratory tract of pigs, which causes Glässer's disease. More than 15 serotypes of H. parasuis have been identified with apparent differences in virulence. In this research, we surveyed the prevalence and distribution of serotypes and known virulence genes of the H. parasuis isolates collected from sick and healthy pigs in Quang Binh and Thua Thien Hue provinces in Central Vietnam. By using bacterial isolation and polymerase chain reaction (PCR), 56 out of 814 (6.9%) samples were positive for H. parasuis. The most prevalent serotypes were serotype 5 (15/56, 26.8%), followed by serotype 2 (13/56, 23.2%) and serotype 4 (10/56, 17.9%). The vta1 was the most frequently detected virulence gene which was present in 62.5% of the strains, followed by vta3 (42.9%), vta2 (39.3%), HPM-1371 (35.7%), capD (30.4%), HPM-1372 (12.5%), lsgB and HPM-1373 (both shared 8.9%). Strong correlations between some serotypes and known virulence genes were observed, in which virulence genes HPM-1371, HPM-1372, vta3, vta2 and capD were mainly clustered in serotypes 5/12, and vta2 clustered in serotype 2. This study presents the first baseline information on the epidemiological characteristics of H. parasuis isolates from Central Vietnam.

A novel experimental intraperitoneal infection model for Haemophilus parasuis in neutropenic guinea pigs

INTRODUCTION

Haemophilus parasuis, one of the major swine pathogens, has at least fifteen different types, all of which have significant economic effects on the global swine industry. The aim of this study was to establish an experimental intraperitoneal infection model for H. parasuis in neutropenic guinea pigs.

METHODS

Intraperitoneal administration of cyclophosphamide and Haemophilus parasuis was conducted in guinea pigs. Clinical signs, gross pathology, and histopathology were observed in neutropenic guinea pigs infected with H. parasuis.

RESULTS

Intraperitoneal administration of 100 mg/kg cyclophosphamide led to immunosuppression with white blood cells, lymphocytes, and neutrophils all <1000 mm³, while no histological tissue damage was observed. Intraperitoneal administration of 10⁹ colony-forming units (CFU) of H. parasuis led to typical respiratory symptoms, 90% morbidity, and 20% mortality in a 72 h-period. Bacteriological screening revealed that multiple organs, including the heart, liver, spleen, lungs, kidneys, and blood, were infected with H. parasuis. The threshold loads of bacteria in blood and the lungs were (7.04 ± 0.53)log₁₀ CFU/mL and (6.24 ± 0.62)log₁₀ CFU/g, respectively, at 3 d after infection. Gross pathology examination showed celiac effusion, intestinal mucosal hemorrhage, and liver, spleen, or lung swelling, necrosis, and hemorrhage. Congestion, mild interstitial pneumonia, inflammatory exudation, and endothelial cell proliferation were observed in the histological examination.

DISCUSSION

All the results suggest that we have established an experimental intraperitoneal infection model for H. parasuis in neutropenic guinea pigs. It is especially useful as a tool for pharmacokinetics, pharmacodynamics, or a pharmacokinetics/pharmacodynamics (PK/PD) model of antimicrobial agents against respiratory disease.

Improvement in the efficiency of natural transformation of Haemophilus parasuis by shuttle-plasmid methylation

Some Haemophilus parasuis strains display resistance to transformation with Escherichia.coli-derived plasmids. This property limits the application of genetic approaches previously developed for H. parasuis. The present study showed that natural transformation with the shuttle plasmid pS2UK led to allelic exchange in H. parasuis strains SH0165 and CF7066. Furthermore, natural transformation with pS2UK yielded allelic exchange mutants in 10 of 17 H. parasuis strains, similar to results using the suicide plasmid pK2UK. Subsequently, 17 H. parasuis strains were transformed with pS2UK by electroporation and 13 obtained the transformants harboring the complete plasmid molecules. As a result, natural transformation of homologous blank strains with the H. parasui-derived plasmids significantly improved the transformation efficiency targeted at obtaining allelic exchange mutants. In addition, shuttle plasmids pS1UG and pSHUK that carried the different homologous arm sequences also displayed the increased transformation efficiency after they were replicated in homologous H. parasuis cells. The approach described here not only improved the efficiency of natural transformation of H. parasuis, but also enlarged the range of transformable H. parasuis strains, thereby enabling application of H. parasuis-specific genetic manipulation techniques in a wider range of isolates.

Characterization of Haemophilus Parasuis Serovar 2 CL120103, a Moderately Virulent Strain in China

Haemophilus parasuis is an important bacterium affecting pigs, causing Glässer’s disease. To further characterize this species, we determined the complete genomic sequence of H. parasuis CL120103, which was isolated from diseased pigs. The strain H. parasuis CL120103 was identified as serovar 2. The size of the largest scaffold is 2,326,318 bp and contains 145 large contigs, with the N50 contig being 20,573 bp in length. The complete genome of H. parasuis CL120103 is 2,305,354 bp in length with 39.97% GC content and contains 2227 protein-coding genes, 19 ribosomal rRNA operons and 60 tRNA genes. Sequence similarity of the genome of H. parasuis CL120103 to the previously sequenced genome of H. parasuis was up to 96% and query cover to 86%. Annotation of the genome of H. parasuis CL120103 identified a number of genes encoding potential virulence factors. These virulence factors are involved in metabolism, adhesion, secretion and LPS biosynthesis. These related genes pave the way to better understand mechanisms underlying metabolic capabilities. The comprehensive genetic and phylogenetic analysis shows that H. parasuis is closely related to Actinobacillus pleuropneumoniae and provides a foundation for future experimental confirmation of the virulence and pathogen-host interactions in H. parasuis.

Epidemiology of Haemophilus parasuis isolates from pigs in China using serotyping, antimicrobial susceptibility, biofilm formation and ERIC-PCR genotyping

Background

Haemophilus parasuis is a commensal organism of the upper respiratory tract of healthy pigs and causes high morbidity and mortality in piglets. The aim of this study was to investigate the epidemiology of H. parasuis in China from 2014 to 2017.

Methods

We characterized 143 H. parasuis isolates by serotyping, antimicrobial susceptibility, biofilm formation and with enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR) assays.

Results

Serotyping revealed serovar 5 as the most prevalent (26.6%) followed by serovars 4 (22.4%), 7 (9.1 %), 13 (6.3%), 12 (5.6 %), and non-typeable (8.4%). In a panel of 23 antimicrobials, the minimum inhibitory concentration 50% (MIC₅₀) were in the range of 0.25–16 μg/mL and MIC₉₀ were 2–>512 μg/mL. A total of 99 isolates of H. parasuis (69.2%) were able to form biofilms and 59.6% (59/99) performed weak biofilm-forming ability. ERIC-PCR revealed a very heterogeneous pattern with 87 clusters.

Discussion

These H. parasuis isolates showed a high serovar and genotypic lineage diversity, different abilities to form biofilms and a high degree of genetic diversity. Biofilm formation was related to antimicrobial susceptibility but there were no statistically significant associations between the antimicrobial susceptibility and either the serovars or the ERIC-PCR clusters. This study showed a high prevalence of high-MIC H. parasuis strains and suggests the need for a continuous surveillance of clinical isolates of H. parasuis.

Transcriptional Profiling of Host Cell Responses to Virulent Haemophilus parasuis: New Insights into Pathogenesis

Haemophilus parasuis is the causative agent of Glässer’s disease in pigs. H. parasuis can cause vascular damage, although the mechanism remains unclear. In this study, we investigated the host cell responses involved in the molecular pathway interactions in porcine aortic vascular endothelial cells (PAVECs) induced by H. parasuis using RNA-Seq. The transcriptome results showed that when PAVECs were infected with H. parasuis for 24 h, 281 differentially expressed genes (DEGs) were identified; of which, 236 were upregulated and 45 downregulated. The 281 DEGs were involved in 136 KEGG signaling pathways that were organismal systems, environmental information processing, metabolism, cellular processes, and genetic information processing. The main pathways were the Rap1, FoxO, and PI3K/Akt signaling pathways, and the overexpressed genes were determined and verified by quantitative reverse transcription polymerase chain reaction. In addition, 252 genes were clustered into biological processes, molecular processes, and cellular components. Our study provides new insights for understanding the interaction between bacterial and host cells, and analyzed, in detail, the possible mechanisms that lead to vascular damage induced by H. parasuis. This may lead to development of novel therapeutic targets to control H. parasuis infection.

Baicalin Inhibits Haemophilus Parasuis-Induced High-Mobility Group Box 1 Release during Inflammation

Haemophilus parasuis (H. parasuis) can cause Glässer’s disease in pigs. However, the molecular mechanism of the inflammation response induced by H. parasuis remains unclear. The high-mobility group box 1 (HMGB1) protein is related to the pathogenesis of various infectious pathogens, but little is known about whether H. parasuis can induce the release of HMGB1 in piglet peripheral blood monocytes. Baicalin displays important anti-inflammatory and anti-microbial activities. In the present study, we investigated whether H. parasuis can trigger the secretion of HMGB1 in piglet peripheral blood monocytes and the anti-inflammatory effect of baicalin on the production of HMGB1 in peripheral blood monocytes induced by H. parasuis during the inflammation response. In addition, host cell responses stimulated by H. parasuis were determined with RNA-Seq. The RNA-Seq results showed that H. parasuis infection provokes the expression of cytokines and the activation of numerous pathways. In addition, baicalin significantly reduced the release of HMGB1 in peripheral blood monocytes induced by H. parasuis. Taken together, our study showed that H. parasuis can induce the release of HMGB1 and baicalin can inhibit HMGB1 secretion in an H. parasuis-induced peripheral blood monocytes model, which may provide a new strategy for preventing the inflammatory disorders induced by H. parasuis.

Characterization of antimicrobial resistance genes in Haemophilus parasuis isolated from pigs in China

Background

Haemophilus parasuis is a common porcine respiratory pathogen that causes high rates of morbidity and mortality in farmed swine. We performed a molecular characterization of antimicrobial resistance genes harbored by H. parasuis from pig farms in China.

Methods

We screened 143 H. parasuis isolates for antimicrobial susceptibility against six fluoroquinolone antibiotics testing by the broth microdilution method, and the presence of 64 antimicrobial resistance genes by PCR amplification and DNA sequence analysis. We determined quinolone resistance determining region mutations of DNA gyrase (gyrA and gyrB) and topoisomerase IV (parC and parE). The genetic relatedness among the strains was analyzed by pulsed-field gel electrophoresis.

Results

Susceptibility test showed that all isolates were low resistance to lomefloxacin (28.67%), levofloxacin (20.28%), norfloxacin (22.38%), ciprofloxacin (23.78%), however, high resistance levels were found to nalidixic acid (82.52%) and enrofloxacin (55.94%). In addition, we found 14 antimicrobial resistance genes were present in these isolates, including bla_TEM-1, bla_ROB-1, ermB, ermA, flor, catl, tetB, tetC, rmtB, rmtD, aadA1, aac(3′)-llc, sul1, and sul2 genes. Interestingly, one isolate carried five antibiotic resistance genes (tetB, tetC, flor, rmtB, sul1). The genes tetB, rmtB, and flor were the most prevalent resistance genes in H. parasuis in China. Alterations in the gyrA gene (S83F/Y, D87Y/N/H/G) were detected in 81% of the strains and parC mutations were often accompanied by a gyrA mutation. Pulsed-field gel electrophoresis typing revealed 51 unique patterns in the isolates carrying high-level antibiotic resistance genes, indicating considerable genetic diversity and suggesting that the genes were spread horizontally.

Discussion

The current study demonstrated that the high antibiotic resistance of H. parasuis in piglets is a combination of transferable antibiotic resistance genes and multiple target gene mutations. These data provide novel insights for the better understanding of the prevalence and epidemiology of antimicrobial resistance in H. parasuis.

The effect of rfaD and rfaF of Haemophilus parasuis on lipooligosaccharide induced inflammation by NF-κB/MAPKs signaling in porcine alveolar macrophages

In Haemophilus parasuis, the rfa cluster has been identified as a virulence-associated factor that is involved in lipooligosaccharide (LOS) biosynthesis. In this study, we assessed the roles of rfaD and rfaF genes in H. parasuis SC096 on LOS-induced pro-inflammatory factors and the related signaling pathways in porcine alveolar macrophages (PAMs) by real-time PCR and western blotting. The results showed that the LOSs of both rfaD and rfaF mutants (ΔrfaD-LOS and ΔrfaF-LOS) significantly decreased the mRNA expression of pro-inflammatory factors (IL-1α, IL-1β, IL-6, IL-8 and TNF-α) in PAMs compared with H. parasuis SC096 LOS (WT-LOS). Furthermore, in ΔrfaD-LOS- and ΔrfaF-LOS-treated cells, IκBα degradation was significantly inhibited and levels of phospho-p65 and phospho-p38 were significantly reduced in PAMs. These findings suggested that the rfaD and rfaF genes mediated LOS induction of pro-inflammatory cytokines in PAMs by regulating the NF-κB and MAPKs signaling pathways during H. parasuis infection.

QseC Mediates Osmotic Stress Resistance and Biofilm Formation in Haemophilus parasuis

Haemophilus parasuis is known as a commensal organism discovered in the upper respiratory tract of swine where the pathogenic bacteria survive in various adverse environmental stress. QseC, a histidine protein kinase of the two-component regulatory systems CheY/QseC, is involved in the environmental adaptation in bacteria. To investigate the role of QseC in coping with the adverse environment stresses and survive in the host, we constructed a qseC mutant of H. parasuis serovar 13 strain (ΔqseC), MY1902. In this study, we found that QseC was involved in stress tolerance of H. parasuis, by the ΔqseC exhibited a decreased resistance to osmotic pressure, oxidative stress, and heat shock. Moreover, the ΔqseC weakened the ability to take up iron and biofilm formation. We also found that the QseC participate in sensing the epinephrine in environment to regulate the density of H. parasuis.

Basic Characterization of Natural Transformation in a Highly Transformable Haemophilus parasuis Strain SC1401

Haemophilus parasuis causes Glässer's disease and pneumonia, incurring serious economic losses in the porcine industry. In this study, natural competence was investigated in H. parasuis. We found competence genes in H. parasuis homologous to ones in Haemophilus influenzae and a high consensus battery of Sxy-dependent cyclic AMP (cAMP) receptor protein (CRP-S) regulons using bioinformatics. High rates of natural competence were found from the onset of stationary-phase growth condition to mid-stationary phase (OD600 from 0.29 to 1.735); this rapidly dropped off as cells reached mid-stationary phase (OD600 from 1.735 to 1.625). As a whole, bacteria cultured in liquid media were observed to have lower competence levels than those grown on solid media plates. We also revealed that natural transformation in this species is stable after 200 passages and is largely dependent on DNA concentration. Transformation competition experiments showed that heterogeneous DNA cannot outcompete intraspecific natural transformation, suggesting an endogenous uptake sequence or other molecular markers may be important in differentiating heterogeneous DNA. We performed qRT-PCR targeting multiple putative competence genes in an effort to compare bacteria pre-cultured in TSB++ vs. TSA++ and SC1401 vs. SH0165 to determine expression profiles of the homologs of competence-genes in H. influenzae. Taken together, this study is the first to investigate natural transformation in H. parasuis based on a highly naturally transformable strain SC1401.

Haemophilus parasuis infection activates NOD1/2-RIP2 signaling pathway in PK-15 cells

Haemophilus parasuis, an important swine pathogen, was recently proven able to invade into endothelial or epithelial cell in vitro. NOD1/2 are specialized NLRs that participate in the recognition of pathogens able to invade intracellularly and therefore, we assessed that the contribution of NOD1/2 to inflammation responses during H. parasuis infection. We observed that H. parasuis infection enhanced NOD2 expression and RIP2 phosphorylation in porcine kidney 15 cells. Our results also showed that knock down of NOD1/2 or RIP2 expression respectively significantly decreased H. parasuis-induced NF-κB activity, while the phosphorylation level of p38, JNK or ERK was not changed. Moreover, real-time PCR result showed that NOD1, NOD2 or RIP2 was involved in the expression of CCL4, CCL5 and IL-8. Inhibition of NOD1 and NOD2 significantly reduced CCL5 promoter activity, even in a more effective way compared with inhibition of TLR.