Haemophilus parasuis: infection, immunity and enrofloxacin

TbpB-based oral mucosal vaccine provides heterologous protection against Glässer's disease caused by different serovars of Spanish field isolates of Glaesserella parasuis

BACKGROUND

Glaesserella parasuis (G. parasuis) is the primary agent of Glässer's disease, significantly affecting nursery and early fattening piglets. Current prophylactic measures, mainly serovar-specific bacterins administered to sows, are limited by maternal immunity, which can interfere with active immunization in piglets. Subunit vaccines containing G. parasuis-specific antigenic molecules show promise but are not yet commercially available. Transferrin-binding proteins (Tbp), which enable G. parasuis to acquire iron in low-iron environments like mucosal surfaces, have been proposed as potential vaccine antigens. The mucosal administration of a TbpB-based subunit vaccine could provide a promising solution to overcome the limitations posed by maternal immunity, offering an effective approach to control the disease in weaning piglets. This study, conducted in two phases, primarily evaluates (days 0-45) the immunogenicity of a two-dose oral mucosal TbpB-based subunit vaccine (TbpBY167A) administered to colostrum-deprived piglets, and subsequently (days 45-52), its heterologous protection by challenging these piglets with four G. parasuis clinical isolates from different TbpB clusters (I, III) and serovars (SV1, SV4, SV5, SV7) recovered from Spanish pig farms.

RESULTS

The oral mucosal administration of the two-dose TbpB-based vaccine induced a robust humoral immune response in immunized colostrum-deprived piglets, significantly increasing IgA and IgM concentration 15 days after the second dose (p < 0.01). Upon challenge with four G. parasuis clinical isolates, the vaccine demonstrated heterologous protection, markedly improving survival rates (OR: 8.45; CI 95%: 4.97-14.36) and significantly reducing clinical signs and lesions, regardless of the TbpB cluster and serovar. The vaccine reduced G. parasuis colonization in the respiratory tract (p < 0.0001) and G. parasuis systemic target tissues, like tarsus and carpus joints, liver, and brain (p < 0.05). Immunohistochemical analysis showed a lower macrophage count in different lung locations of immunized piglets (p < 0.0001).

CONCLUSIONS

This study demonstrates that oral mucosal administration of the TbpBY167A subunit vaccine in piglets provides effective heterologous protection against diverse virulent European G. parasuis field isolates, significantly reducing bacterial colonization and dissemination. This vaccine offers a promising alternative to traditional bacterins, overcoming limitations due to maternal immunity, and represents a strong candidate for universal vaccination against Glässer's disease.

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.

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

BACKGROUND

Glaesserella parasuis (G. parasuis) is the causative agent of Glässer's disease, which causes significant economic losses in the swine industry. However, research on the pathogenesis of G. parasuis has been hampered by the lack of a simple and efficient marker-free knockout system.

RESULTS

In this study, a marker-free knockout system was developed for G. parasuis using a temperature-sensitive vector. By alternating the incubation of transformants at 30°C and 37°C, we optimized the screening process for this system. The system was successfully applied to knockout the KanR cassette from JS0135ΔnanH::KanR, achieving a knockout efficiency of 90% in the final round of screening. To confirm that temperature variation was a key factor, we proceeded with knocking out the nanH and apd genes in the CF7066 strain. The knockout efficiency reached up to 100%, with the shortest screening time being only four days. The knockout of the nanH gene resulted in a significant reduction in the growth vitality of the strains, while the knockout of the apd gene led to an approximate 56% improvement in the adhesion rate. Additionally, we observed that the expression of recombinant genes in transformants was higher at 30℃ than at 37℃, with the recC gene being upregulated approximately 7-fold. In contrast, there was almost no difference in the expression of recombinant genes between 30℃ and 37℃ in the wild-type strains. This discrepancy was likely due to an elevated copy number of target plasmids at 30℃, which may have resulted in the enhanced expression of recombinant genes.

CONCLUSIONS

In conclusion, this newly developed gene knockout system for G. parasuis presents a valuable tool for advancing research on this organism.

Molecular characterization of the integrative and conjugative elements harbouring multidrug resistance genes in Glaesserella parasuis

It is widely known that integrative and conjugative elements (ICEs) play an important role in the transmission of resistance genes and other exogenous genes. The present study aimed to characterize the three novel ICEs including ICEGpa76, ICEGpa44, and ICEGpa11, from Glaesserella parasuis. The ICEs from G. parasuis strains d76, Z44, and XP11 were predicted and identified by whole-genome sequencing (WGS) analysis, ICEfinder, and PCR. Characterization of G. parasuis strains carrying ICEs were determined by conjugation assay, antimicrobial susceptibility testing, WGS, phylogenetic analysis, and comparative sequence analysis.The WGS results showed that three ICEs from G. parasuis have a common genetic backbone belonging to characteristics ofthe ICEHpa1 family. The sequence comparison showed that the ICEHpa1 family has five hot spots (HSs) determined by IS6, IS110, and IS256. Moreover, two variable regions (VRs), VR1 and VR2 were determined by multidrug resistance genes and the rearrangement hotspot (rhs) family, respectively. VR1 consists of multidrug resistance genes, ISApl1s, and other accessory genes, while VR2 is composed of IS4, rhs family, transposase, and hypothetical protein genes. Conjugation experiments and MICs revealed that three ICEs could be transferred to G. parasuis strain IV52, indicating these three ICEs could be transmitted horizontally among G. parasuis strains. Additionally, the difference in resistance genes from ICEs might be due to the insertion function of the ISApl1s in VR1, and the rhs family in VR2 might evolve andthen be stably inherited in G. parasuis. These results further elucidated the transmission mechanism of exogenous genes in G. parasuis.

Intramuscular therapeutic doses of enrofloxacin affect microbial community structure but not the relative abundance of fluoroquinolones resistance genes in swine manure

Livestock manure is a major source of veterinary antibiotics and antibiotic resistance genes (ARGs). Elucidation of the residual characteristics of ARGs in livestock manure following the administration of veterinary antibiotics is critical to assess their ecotoxicological effects and environmental contamination risks. Here, we investigated the effects of enrofloxacin (ENR), a fluoroquinolone antibiotic commonly used as a therapeutic drug in animal husbandry, on the characteristics of ARGs, mobile genetic elements, and microbial community structure in swine manure following its intramuscular administration for 3 days and a withdrawal period of 10 days. The results revealed the highest concentrations of ENR and ciprofloxacin (CIP) in swine manure at the end of the administration period, ENR concentrations in swine manure in groups L and H were 88.67 ± 45.46 and 219.75 ± 88.05 mg/kg DM, respectively. Approximately 15 fluoroquinolone resistance genes (FRGs) and 48 fluoroquinolone-related multidrug resistance genes (F-MRGs) were detected in swine manure; the relative abundance of the F-MRGs was considerably higher than that of the FRGs. On day 3, the relative abundance of qacA was significantly higher in group H than in group CK, and no significant differences in the relative abundance of other FRGs, F-MRGs, or MGEs were observed between the three groups on day 3 and day 13. The microbial community structure in swine manure was significantly altered on day 3, and the altered community structure was restored on day 13. The FRGs and F-MRGs with the highest relative abundance were qacA and adeF, respectively, and Clostridium and Lactobacillus were the dominant bacterial genera carrying these genes in swine manure. In summary, a single treatment of intramuscular ENR transiently increased antibiotic concentrations and altered the microbial community structure in swine manure; however, this treatment did not significantly affect the abundance of FRGs and F-MRGs.

LRRC8A promotes Glaesserella parasuis cytolethal distending toxin-induced p53-dependent apoptosis in NPTr cells

Glaesserella parasuis is an early colonizer of the swine upper respiratory tract and can break through the respiratory barrier for further invasion. However, the mechanisms underlying G. parasuis increases epithelial barrier permeability remain unclear. This study demonstrates that G. parasuis cytolethal distending toxin (CDT) induces p53-dependent apoptosis in new-born piglet tracheal (NPTr) cells. Moreover, we report for the first time that leucine-rich repeat-containing protein 8A (LRRC8A), an essential subunit of the volume-regulated anion channel (VRAC), involves in apoptosis of NPTr cells mediated by G. parasuis CDT. Pharmacological inhibition of VRAC with either PPQ-102 or NS3728 largely attenuated CDT-induced apoptosis in NPTr cells. Additionally, experiments with cells knocked down for LRRC8A using small interfering ribonucleic acid (siRNA) or knocked out LRRC8A using CRISPR/Cas9 technology showed a significant reduction in CDT-induced apoptosis. Conversely, re-expression of Sus scrofa LRRC8A in LRRC8A-/- NPTr cells efficiently complemented the CDT-induced apoptosis. In summary, these findings suggest that LRRC8A is pivotal for G. parasuis CDT-induced apoptosis, providing novel insights into the mechanism of apoptosis caused by CDT.

Characterization of the plasmids harbouring the florfenicol resistance gene floR in Glaesserella parasuis and Actinobacillus indolicus

OBJECTIVES

The aim of this study was to characterize the floR-carrying plasmids originating from Glaesserella parasuis and Actinobacillus indolicus isolated from pigs with respiratory disease in China.

METHODS

A total of 125 G. parasuis and 28 A. indolicus strains collected between 2009 and 2022 were screened for florfenicol resistance. Characterization of floR-positive isolates and plasmids were determined by antimicrobial susceptibility testing, serotyping, multilocus sequence typing (MLST), conjugation and transformation assays, whole-genome sequencing (WGS), and phylogenetic analysis.

RESULTS

One A. indolicus and six G. parasuis were identified as positive for floR. The six G. parasuis were assigned to four different serovars, including serovars 6, 7, 9, and unknown. In addition to strain XP11, six floR genes were located on plasmids. The six floR-bearing plasmids could be transformed into Pasteurella multocida and divided into two different types, including ∼5000 bp and ∼6000 bp plasmids. The ∼5000 bp plasmids consisting of rep, lysR, mobB, and floR genes, exhibited high similarity among Pasteurellaceae bacteria. Furthermore, the ∼6000 bp plasmids, consisting of rep, lysR, mobC, mobA/L, and floR genes, showed high similarity between G. parasuis and Actinobacillus Spp. Notably, WGS results showed that the floR modules of the two types of plasmids could be transferred and integrated into the diverse Pasteurellaceae- origined plasmids.

CONCLUSION

This study firstly reported the characterization of floR-carrying plasmids from A. indolicus and a non-virulent serovar of G. parasuis in pigs in China and elucidated the transmission mechanism of the floR resistance gene among the Pasteurellaceae family.

Porcine circovirus type 2 infection inhibits macrophage M1 polarization induced by other pathogens via viral capsid protein and host gC1qR protein

Porcine circovirus type 2 (PCV2) has been proven to co-infect with a variety of pathogens and cause immunosuppression. Previously, we have reported that PCV2 infection attenuates the production of pro-inflammatory cytokines induced by other pathogens in porcine macrophages. However, whether PCV2 can affect M1-type macrophage polarization induced by other pathogens is less well reported. Herein, we found that PCV2 infection suppressed M1 macrophage production induced by porcine reproductive and respiratory syndrome virus (PRRSV) and Haemophilus parasuis (H. parasuis) in the lung and promoted the proliferation of these pathogens in the piglets. Consistently, we confirmed that PCV2 inhibits M1 macrophage production and its associated gene expression in porcine alveolar macrophages (PAMs) both ex vivo and in vitro. Meanwhile, PCV2 inhibited lipopolysaccharide (LPS)-induced pro-inflammatory cytokines in vitro in a time- and dose-dependent manner. In PCV2-infected cells, LPS-induced signal transducer and activator of transcription (STAT1) phosphorylation and its nuclear translocation were decreased. Based on these findings, we further identified a role for PCV2 capsid protein (Cap) in LPS-induced M1 macrophage-associated genes and found that PCV2 Cap can significantly reduce STAT1 phosphorylation and its nuclear translocation, as well as the production of M1 macrophage-related genes. As the binding protein of PCV2 Cap, gC1qR protein was also associated with this inhibition process. gC1qR-binding activity-deficient PCV2 Cap mutated protein (Cap RmA) appeared an attenuated inhibitory effect on other pathogen-induced polarization of M1-type macrophages, suggesting that the inhibitory effect of PCV2 infection on M1-type macrophage polarization induced by other pathogens is dependent on Cap protein and the host gC1qR protein. Altogether, our results demonstrate that PCV2 infection inhibits macrophage M1 polarization induced by other pathogens via capsid and host gC1qR protein modulating JAK/STAT signaling.

Modeling Co-Infection by Streptococcus suis and Haemophilus parasuis Reveals Influences on Biofilm Formation and Host Response

Streptococcus suis (S. suis) and Haemophilus parasuis (H. parasuis) are two primary pathogens currently affecting the porcine industry. They often cause encephalitis and arthritis. They also frequently co-infect in clinical settings. In the current study, we identified significant correlations between S. suis and H. parasuis. The results from CI versus RIR suggested that S. suis and H. parasuis were competitive in general. Compared to mono-species biofilm, the biomass, bio-volume, and thickness of mixed-species biofilms were significantly higher, which was confirmed using crystal violet staining, confocal laser scanning microscopy, and scanning electron microscopy. Compared to mono-species biofilm, the viable bacteria in the mixed-species biofilms were significantly lower, which was confirmed using the enumeration of colony-forming units (CFU cm^-2). The susceptibility of antibiotics in the co-culture decreased in the planktonic state. In contrast, biofilm state bacteria are significantly more difficult to eradicate with antibiotics than in a planktonic state. Whether in planktonic or biofilm state, the expression of virulence genes of S. suis and H. parasuis in mixed culture was very different from that in single culture. Subsequently, by establishing a mixed infection model in mice, we found that the colonization of the two pathogens in organs increased after mixed infection, and altered the host's inflammatory response. In summary, our results indicate that S. suis and H. parasuis compete when co-cultured in vitro. Surprisingly, S. suis and H. parasuis synergistically increased colonization capacity after co-infection in vivo. This study elucidated the interaction between S. suis and H. parasuis during single infections and co-infections. Future studies on bacterial disease control and antibiotic treatment should consider the interaction of mixed species.

Novel Multiplex PCR Assay and Its Application in Detecting Prevalence and Antibiotic Susceptibility of Porcine Respiratory Bacterial Pathogens in Guangxi, China

Porcine respiratory disease complex (PRDC) is a serious disease caused by multiple pathogens which inflicts huge economic losses on the pig industry. Investigating the epidemiology of porcine respiratory bacterial pathogens (PRBPs) in specific geographic areas and exploring the antibiotic susceptibility of local strains will contribute to the prevention and control of PRDC. However, the epidemiology of PRBPs in Guangxi Province remains unclear, and existing diagnostic methods have multiple limitations, such as high costs and the detection of only a single pathogen at a time. In this study, we developed a multiplex PCR assay for Streptococcus suis, Glaesserella parasuis, Actinobacillus pleuropneumoniae, Pasteurella multocida, and Mycoplasma hyopneumoniae, and investigated the prevalence of PRBPs in pigs with respiratory symptoms in Guangxi Province. The isolates from positive samples were subjected to susceptibility tests to 16 antibiotics. Our results indicated that of the 664 samples from pigs with respiratory symptoms, 433 (65.21%), 320 (48.19%), 282 (42.47%), 23 (3.46%), and 9 (1.36%), respectively, carried each of these 5 pathogens; 533 samples were positive; and 377 (56.78%) carried multiple pathogens simultaneously. The dominant PRBPs in pigs with respiratory symptoms in Guangxi province were S. suis, G. parasuis, and A. pleuropneumoniae, which frequently co-infected swine herds. Most of the isolates (A. pleuropneumoniae, G. parasuis, S. suis, and P. multocida) were sensitive to cefquinome, ceftiofur, trimethoprim-sulfamethoxazole (TMP-SMX), and tiamulin antibiotics. We developed a rapid specific multiplex PCR assay for PRBPs. Our findings provide new information on the epidemiology of PRBPs in Guangxi Province and offer a reference for developing drug targets against PRDC. IMPORTANCE Pigs are closely associated with humans as the most common food animals and the vectors of numerous pathogens. PRDC, caused by multiple pathogens, is a serious disease that can cause growth retardation in swine and even sudden death. Due to the droplet transmission of PRBP and the similar clinical signs of different pathogen infections, most pig farms struggle to identify and control PRBPs, leading to the abuse of antibiotics. In addition, some PRBPs have the potential to infect humans and threaten human health. Therefore, this study developed a multiplex PCR method targeting PRBPs, investigated the prevalence of these pathogens, and tested their antibiotic susceptibility. Our studies have important implications for public health safety and the development of the pig 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.

Screening of linear B-cell epitopes and its proinflammatory activities of Haemophilus parasuis outer membrane protein P2

Haemophilus parasuis is a commensal organism of the upper respiratory tract of pigs, but virulent strains can cause Glässer's disease, resulting in significant economic losses to the swine industry. OmpP2 is an outer membrane protein of this organism that shows considerable heterogeneity between virulent and non-virulent strains, with classification into genotypes I and II. It also acts as a dominant antigen and is involved in the inflammatory response. In this study, 32 monoclonal antibodies (mAbs) against recombinant OmpP2 (rOmpP2) of different genotypes were tested for reactivity to a panel of OmpP2 peptides. Nine linear B cell epitopes were screened, including five common genotype epitopes (Pt1a, Pt7/Pt7a, Pt9a, Pt17, and Pt19/Pt19a) and two groups of genotype-specific epitopes (Pt5 and Pt5-II, Pt11/Pt11a, and Pt11a-II). In addition, we used positive sera from mice and pigs to screen for five linear B-cell epitopes (Pt4, Pt14, Pt15, Pt21, and Pt22). After porcine alveolar macrophages (PAMs) were stimulated with overlapping OmpP2 peptides, we found that the epitope peptides Pt1 and Pt9, and the loop peptide Pt20 which was adjacent epitopes could all significantly upregulated the mRNA expression levels of IL-1α, IL-1β, IL-6, IL-8, and TNF-α. Additionally, we identified epitope peptides Pt7, Pt11/Pt11a, Pt17, Pt19, and Pt21 and loop peptides Pt13 and Pt18 which adjacent epitopes could also upregulate the mRNA expression levels of most proinflammatory cytokines. This suggested that these peptides may be the virulence-related sites of the OmpP2 protein, with proinflammatory activity. Further study revealed differences in the mRNA expression levels of proinflammatory cytokines, including IL-1β and IL-6, between genotype-specific epitopes, which may be responsible for pathogenic differences between different genotype strains. Here, we profiled a linear B-cell epitope map of the OmpP2 protein and preliminarily analyzed the proinflammatory activities and effects of these epitopes on bacterial virulence, providing a reliable theoretical basis for establishing a method to distinguish strain pathogenicity and to screen candidate peptides for subunit vaccines.

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.

Macleaya cordata extract modulates inflammation via inhibition of the NF-κB and MAPK signaling pathways in porcine alveolar macrophages induced by Glaesserella parasuis

Glässer's disease in pigs is associated with infection by Glaesserella parasuis and is characterized by pneumonia-like symptoms, fibrinous polyserositis, polyarthritis, and meningitis. Macleaya cordata, a commonly used traditional Chinese medication, has been shown to have anti-inflammatory, antiviral, antioxidative, antimicrobial, insecticidal, and antitumor properties. However, the anti-inflammatory effects of M. cordata on G. parasuis stimulation are still poorly understood. This study explored the anti-inflammatory effects and mechanisms of M. cordata extract on G. parasuis-induced inflammatory responses, via the nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways, in porcine alveolar macrophages (PAMs). Porcine alveolar macrophages, when stimulated with G. parasuis, initiated transcription of interleukin (IL)-1α, IL-1β, IL-6, IL-8, and tumor necrosis factor alpha (TNF-α). Furthermore, p65, IκBα, p38, extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK) phosphorylation were upregulated via the NF-κB and MAPK signaling pathways. However, treatment with M. cordata extract inhibited transcription of IL-1α, IL-1β, IL-6, IL-8, and TNF-α and reduced p65, IκBα, p38, ERK, and JNK phosphorylation, by inhibiting activation of the NF-κB and MAPK signaling pathways in PAMs induced by G. parasuis. These findings reveal that M. cordata extract can reverse the inflammatory effect initiated by G. parasuis in vitro and that it possesses significant immunosuppression activity; thus, it may offer a novel strategy for controlling and treating G. parasuis infection.

Studying the Interaction of Neutrophils and Glaesserella Parasuis Indicates a Serotype Independent Benefit from Degradation of NETs

Glaesserella (G.) parasuis is one of the most important porcine pathogens causing Glaesser’s disease. Neutrophil granulocytes are the major counteracting cell type of the innate immune system, which contribute to the host defense by phagocytosis or the formation of neutrophil extracellular traps (NETs). Recently, NET-formation has been shown to facilitate the survival of bacteria from the Pasteurellaceae family. However, the interaction of NETs and G. parasuis is unclear so far. In this study, we investigated the interplay of three G. parasuis serotypes with porcine neutrophils. The production of reactive oxygen species by neutrophils after G. parasuis infection varied slightly among the serotypes but was generally low and not significantly influenced by the serotypes. Interestingly, we detected that independent of the serotype of G. parasuis, NET formation in neutrophils was induced to a small but significant extent. This phenomenon occurred despite the ability of G. parasuis to release nucleases, which can degrade NETs. Furthermore, the growth of Glaesserella was enhanced by external DNases and degraded NETs. This indicates that Glaesserella takes up degraded NET components, supplying them with nicotinamide adenine dinucleotide (NAD), as this benefit was diminished by inhibiting the 5′-nucleotidase, which metabolizes NAD. Our results indicate a serotype-independent interaction of Glaesserella with neutrophils by inducing NET-formation and benefiting from DNA degradation.

Recovery of the Structure and Function of the Pig Manure Bacterial Community after Enrofloxacin Exposure

A stable intestinal bacterial community balance is beneficial for animal health. Enrofloxacin is widely used in animal husbandry as a therapeutic drug, but it can cause intestinal environmental imbalance.

Methylome and Transcriptome-Based Integration Analysis Identified Molecular Signatures Associated With Meningitis Induced by Glaesserella parasuis

Glaesserella parasuis (G. parasuis) can elicit serious inflammatory responses and cause meningitis in piglets. Previous epigenetic studies have indicated that alterations in host DNA methylation may modify the inflammatory response to bacterial infection. However, to date, genome-wide analysis of the DNA methylome during meningitis caused by G. parasuis infection is still lacking. In this study, we employed an unbiased approach using deep sequencing to profile the DNA methylome and transcriptome from G. parasuis infected porcine brain (cerebrum) and integrated the data to identify key differential methylation regions/sites involved in the regulation of the inflammatory response. Results showed that DNA methylation patterns and gene expression profiles from porcine brain were changed after G. parasuis infection. The majority of the altered DNA methylation regions were found in the intergenic regions and introns and not associated with CpG islands, with only a low percentage occurring at promoter or exon regions. Integrated analysis of the DNA methylome and transcriptome identified a number of inversely and positively correlated genes between DNA methylation and gene expression, following the criteria of |log₂FC| > 0.5, |diffMethy| > 0.1, and P < 0.05. Differential expression and methylation of two significant genes, semaphoring 4D (SEMA4D) and von Willebrand factor A domain containing 1 (VWA1), were validated by qRT-PCR and bisulfite sequencing. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses demonstrated that DNA methylation inversely correlated genes in G. parasuis infected porcine brains were mainly involved with cell adhesion molecules (CAMs), bacterial invasion of epithelial cells, RIG-1-like receptor signaling pathways, and hematopoietic cell lineage signaling pathways. In addition, a protein-protein interaction network of differentially methylated genes found potential candidate molecular interactions relevant to the pathology of G. parasuis infection. To the best of our knowledge, this is the first attempt to integrate the DNA methylome and transcriptome data from G. parasuis infected porcine brains. Our findings will help understanding the contribution of genome-wide DNA methylation to the pathogenesis of meningitis in pigs and developing epigenetic biomarkers and therapeutic targets for the treatment of G. parasuis induced meningitis.

Glaesserella parasuis serotype 4 HPS4-YC disrupts the integrity of the swine tracheal epithelial barrier and facilitates bacterial translocation

Glaesserella parasuis (G. parasuis) is a commensal bacterium in the upper respiratory tract of pigs that can also cause the swine Glässer disease, which induces an intensive inflammatory response and results in significant economic losses to the swine industry worldwide. G. parasuis can cause disease through infection of the respiratory tract, resulting in systemic infection, but the mechanism is largely unknown. Recently we showed that Glaesserella parasuis serotype 4 (GPS4) increased swine tracheal epithelial barrier permeability, resulting in easier bacterial translocation. Tight junction proteins (TJ) play a crucial role in maintaining the integrity and impermeability of the epithelial barrier. GPS4 decreased the expression of the TJ ZO-1 and occludin in swine tracheal epithelial cells (STEC). Furthermore, the proinflammatory cytokines IL-6, IL-8 and TNF-α were significantly upregulated in GPS4-infected STEC, and both the MAPK and NF-κB signaling pathways were activated and contributed to the expression of TNF-α. We demonstrate that the production of proinflammatory cytokines, especially TNF-α, during GPS4 infection was involved in barrier dysfunction. Additionally, animal challenge experiments confirmed that GPS4 infection downregulated TJ in the lungs of piglets and induced a severe inflammatory response. In general, G. parasuis infection downregulated the expression of TJ and induced massive secretion of proinflammatory cytokines, resulting in epithelial barrier disruption and favoring bacterial infection. This study allowed us to better understand the mechanism by which G. parasuis crosses the respiratory tract of pigs.

Application of mouse model for evaluation of recombinant LpxC and GmhA as novel antigenic vaccine candidates of Glaesserella parasuis serotype 13

Glaesserella parasuis (G. parasuis) has been one of the bacteria affecting the large-scale swine industry. Lack of an effective vaccine has limited control of the disease, which has an effect on prevalence. In order to improve the cross-protection of vaccines, development on subunit vaccines has become a hot spot. In this study, we firstly cloned the lpxC and gmhA genes from G. parasuis serotype 13 isolates, and expressed and purified their proteins. The results showed that LpxC and GmhA can stimulate mice to produce IgG antibodies. Through testing the cytokine levels of interleukin 4 (IL-4), IL-10 and interferon-γ (IFN-γ), it is found that recombinant GmhA, the mixed LpxC and GmhA can stimulate the body to produce Th1 and Th2 immune responses, while recombinant LpxC and inactivated bacteria can only produce Th2 immune responses. On the protection rate for mice, recombinant LpxC, GmhA and the mixture of LpxC and GmhA can provide 50%, 50% and 60% protection for lethal dose of G. parasuis infection, respectively. The partial protection achieved by the recombinant LpxC and GmhA supports their potential as novel vaccine candidate antigens against G. parasuis.

Comparison of De Novo Assembly Strategies for Bacterial Genomes

(1) Background: Short-read sequencing allows for the rapid and accurate analysis of the whole bacterial genome but does not usually enable complete genome assembly. Long-read sequencing greatly assists with the resolution of complex bacterial genomes, particularly when combined with short-read Illumina data. However, it is not clear how different assembly strategies affect genomic accuracy, completeness, and protein prediction. (2) Methods: we compare different assembly strategies for Haemophilus parasuis, which causes Glässer's disease, characterized by fibrinous polyserositis and arthritis, in swine by using Illumina sequencing and long reads from the sequencing platforms of either Oxford Nanopore Technologies (ONT) or SMRT Pacific Biosciences (PacBio). (3) Results: Assembly with either PacBio or ONT reads, followed by polishing with Illumina reads, facilitated high-quality genome reconstruction and was superior to the long-read-only assembly and hybrid-assembly strategies when evaluated in terms of accuracy and completeness. An equally excellent method was correction with Homopolish after the ONT-only assembly, which had the advantage of avoiding hybrid sequencing with Illumina. Furthermore, by aligning transcripts to assembled genomes and their predicted CDSs, the sequencing errors of the ONT assembly were mainly indels that were generated when homopolymer regions were sequenced, thus critically affecting protein prediction. Polishing can fill indels and correct mistakes. (4) Conclusions: The assembly of bacterial genomes can be directly achieved by using long-read sequencing techniques. To maximize assembly accuracy, it is essential to polish the assembly with homologous sequences of related genomes or sequencing data from short-read technology.

LncRNA-MEG3 Regulates the Inflammatory Responses and Apoptosis in Porcine Alveolar Macrophages Infected with Haemophilus parasuis Through Modulating the miR-210/TLR4 Axis

Haemophilus parasuis (H. parasuis, HPS) can elicit serious inflammatory responses and cause enormous economic loss to swine industry worldwide. However, the factors responsible for systemic infection and inflammatory responses of HPS have not yet been fully clarified. In this study, we found that lncRNA-MEG3 was significantly up-regulated in porcine alveolar macrophages (PAMs) infected with HPS. The gain- and loss-of-function analysis confirmed that lncRNA-MEG3 participated in the inflammatory responses and apoptosis in HPS-infected PAMs, which was assessed via several inflammatory cytokine genes (TNF-α, IL-1β, and IL-6) and apoptotic factors (Bcl-2, Bax, and C-caspase-3). Based on biotin-labeled RNA pull-down assay, we found that lncRNA-MEG3 bound with miR-210 in HPS-infected PAMs. Based on both overexpression and knockdown analysis of lncRNA-MEG3, our results indicated that lncRNA-MEG3 promoted the expression of TLR4 in HPS-infected PAMs. Using dual-luciferase reporter assays, we showed that lncRNA-MEG3 positively regulated the expression of TLR4 gene in HPS-infected PAMs through miR-210 pathway. Taken together, our results indicated that lncRNA-MEG3 participated in the inflammatory responses and apoptosis in HPS-infected PAMs through modulating the miR-210/TLR4 axis. The results from this investigation provided significant information for a novel target to control HPS infection in swine.

Baicalin Protects Vascular Tight Junctions in Piglets During Glaesserella parasuis Infection

Glaesserella parasuis (G. parasuis) can cause Glässer's disease and severely affect swine industry worldwide. This study is an attempt to address the issue of the capability of G. parasuis to damage the vascular barrier and the effects of baicalin on vascular tight junctions (TJ) in order to investigate the interactions between the pathogen and the porcine vascular endothelium. Piglets were challenged with G. parasuis and treated with or without baicalin. The expressions of vascular TJ genes were examined using RT-PCR. The distribution patterns of TJ proteins were detected by immunofluorescence. The involved signaling pathways were determined by Western blot assays on related proteins. G. parasuis can downregulate TJ expression and disrupt the distribution of TJ proteins. Baicalin can alleviate the downregulation of vascular TJ mRNA, maintain the distribution, and prevent the abnormalities of TJ. These results provide ample evidence that baicalin has the capacity to protect vascular TJ damaged by G. parasuis through inhibiting PKC and MLCK/MLC pathway activation. As a result, baicalin is a promising candidate for application as a natural agent for the prevention and control of G. parasuis infection.

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.

The Role of Antibodies Against the Crude Capsular Extract in the Immune Response of Porcine Alveolar Macrophages to In Vitro Infection of Various Serovars of Glaesserella (Haemophilus) parasuis

In Glässer’s disease outbreaks, Glaesserella (Haemophilus) parasuis has to overcome the non-specific immune system in the lower respiratory tract, the alveolar macrophages. Here we showed that porcine alveolar macrophages (PAMs) were able to recognize and phagocyte G. parasuis with strain-to-strain variability despite the presence of the capsule in virulent (serovar 1, 5, 12) as well in avirulent strains (serovar 6 and 9). The capsule, outer membrane proteins, virulence-associated autotransporters, cytolethal distending toxins and many other proteins have been identified as virulence factors of this bacterium. Therefore, we immunized pigs with the crude capsular extract (cCE) from the virulent G. parasuis CAPM 6475 strain (serovar 5) and evaluated the role of the anti-cCE/post-vaccinal IgG in the immune response of PAMs to in vitro infection with various G. parasuis strains. We demonstrated the specific binding of the antibodies to the cCE by Western-blotting assay and immunoprecipitation as well as the specific binding to the strain CAPM 6475 in transmission electron microscopy. In the cCE, we identified several virulence-associated proteins that were immunoreactive with IgG isolated from sera of immunized pigs. Opsonization of G. parasuis strains by post-vaccinal IgG led to enhanced phagocytosis of G. parasuis by PAMs at the first two hours of infection. Moreover, opsonization increased the oxidative burst and expression/production of both pro- and anti-inflammatory cytokines. The neutralizing effects of these antibodies on the antioxidant mechanisms of G. parasuis may lead to attenuation of its virulence and pathogenicity in vivo. Together with opsonization of bacteria by these antibodies, the host may eliminate G. parasuis in the infection site more efficiently. Based on these results, the crude capsular extract is a vaccine candidate with immunogenic properties.

Altered oral microbiota composition associated with recurrent aphthous stomatitis in young females

Oral microbiota has been implicated in pathogenesis of recurrent aphthous stomatitis (RAS), which is a common mucosal disorder with unclear etiology. This study has explored the association between oral microbiota disorder and RAS in high-risk young female population.Forty-five young females were enrolled, including 24 RAS patients and 21 healthy individuals. Oral microbiome was analyzed by Illumina Miseq sequencing.Oral microbiota associated with RAS was characterized by the lower alpha-diversity indices (Chao1 and ACE). Several infectious pathogens increased in RAS, such as genera Actinobacillus, Haemophilus, Prevotella and Vibrio. The PICRUSt analysis indicated that the oral microbiota might be related with the up-regulation of genes involving infectious and neurodegenerative diseases, environmental adaptation, the down-regulation of genes involving basal metabolism, such as carbohydrate, energy, and amino acid metabolism.This study indicated that oral microbiota may play a significant role in RAS development.

Protective Effects of Baicalin on Peritoneal Tight Junctions in Piglets Challenged with Glaesserella parasuis

Glaesserella parasuis (G. parasuis) causes inflammation and damage to piglets. Whether polyserositis caused by G. parasuis is due to tight junctions damage and the protective effect of baicalin on it have not been examined. Therefore, this study aims to investigate the effects of baicalin on peritoneal tight junctions of piglets challenged with G. parasuis and its underlying molecular mechanisms. Piglets were challenged with G. parasuis and treated with or without baicalin. RT-PCR was performed to examine the expression of peritoneal tight junctions genes. Immunofluorescence was carried out to detect the distribution patterns of tight junctions proteins. Western blot assays were carried out to determine the involved signaling pathways. Our data showed that G. parasuis infection can down-regulate the tight junctions expression and disrupt the distribution of tight junctions proteins. Baicalin can alleviate the down-regulation of tight junctions mRNA in peritoneum, prevent the abnormalities and maintain the continuous organization of tight junctions. Our results provide novel evidence to support that baicalin has the capacity to protect peritoneal tight junctions from G. parasuis-induced inflammation. The protective mechanisms of baicalin could be associated with inhibition of the activation of PKC and MLCK/MLC signaling pathway. Taken together, these data demonstrated that baicalin is a promising natural agent for the prevention and treatment of G. parasuis infection.

Relationships among Fecal, Air, Oral, and Tracheal Microbial Communities in Pigs in a Respiratory Infection Disease Model

The association of the lower respiratory tract microbiome in pigs with that of other tissues and environment is still unclear. This study aimed to describe the microbiome of tracheal and oral fluids, air, and feces in the late stage of Mycoplasma hyopneumoniae infection in pigs, and assess the association between the tracheal microbiome and those from air, feces, and oral fluids. Tracheal fluids (n = 73), feces (n = 71), oropharyngeal fluids (n = 8), and air (n = 12) were collected in seeder pigs (inoculated with M. hyopneumoniae) and contact pigs (113 days post exposure to seeder pigs). After DNA extraction, the V4 region from 16S rRNA gene was sequenced and reads were processed using Divisive Amplicon Denoising Algorithm (DADA2). Clostridium and Streptococcus were among the top five genera identified in all sample types. Mycoplasma hyopneumoniae in tracheal fluids was associated with a reduction of diversity and increment of M. hyorhinis, Glaesserella parasuis, and Pasteurella multocida in tracheal fluids, as well as a reduction of Ruminiclostridium, Barnesiella, and Lactobacillus in feces. Air contributed in a greater proportion to bacteria in the trachea compared with feces and oral fluids. In conclusion, evidence suggests the existence of complex interactions between bacterial communities from distant and distinct niches.

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.

Effects of respiratory disease on Kele piglets lung microbiome, assessed through 16S rRNA sequencing

Background and Aim

Due to the incomplete development of the immune system in immature piglets, the respiratory tract is susceptible to invasion by numerous pathogens that cause a range of potential respiratory diseases. However, few studies have reported the changes in pig lung microorganisms during respiratory infection. Therefore, we aimed to explore the differences in lung environmental microorganisms between healthy piglets and piglets with respiratory diseases.

Materials and Methods

Histopathological changes in lung sections were observed in both diseased and healthy pigs. Changes in the composition and abundance of microbiomes in alveolar lavage fluid from eleven 4-week-old Chinese Kele piglets (three clinically healthy and eight diseased) were studied by IonS5™ XL sequencing of the bacterial16S rRNA genes.

Results

Histopathological sections showed that diseased pigs displayed more lung lesions than healthy pigs. Diseased piglets harbored lower bacterial operational taxonomic units, α-diversity, and bacterial community complexity in comparison to healthy piglets. Taxonomic composition analysis showed that in the diseased piglets, the majority of flora was composed of Ureaplasma, Mycoplasma, and Actinobacillus; while Actinobacillus, Sphingomonas, and Stenotrophomonas were dominant in the control group. The abundance of Ureaplasma was significantly higher in ill piglets (p<0.05), and the phylogenetic tree indicated that Ureaplasma was clustered in Ureaplasma diversum, a conditional pathogen that has the potential to affect the swine respiratory system.

Conclusion

The results of this study show that the microbial species and structure of piglets' lungs were changed during respiratory tract infection. The finding of Ureaplasma suggested that besides known pathogens such as Mycoplasma and Actinobacillus, unknown pathogens can exist in the respiratory system of diseased pigs and provide a potential basis for clinical treatment.

Antibacterial effect of Blumea balsamifera DC. essential oil against Haemophilus parasuis

Haemophilus parasuis (H. parasuis), the cause of the Glasser's disease, is a potentially pathogenic gram-negative organism that colonizes the upper respiratory tract of pigs. The extraction of Blumea balsamifera DC., as a traditional Chinese herb, has shown great bacteriostatic effect against several common bacteria. To study the antibacterial effect on H. parasuis in vitro, this study evaluated the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of Blumea balsamifera DC. essential oil (BBO) as well as morphological changes in H. parasuis treated with it. Furthermore, changes in expression of total protein and key virulence factors were also assessed. Results showed that the MIC and MBC were 0.625 and 1.25 μg/mL, respectively. As the concentration of BBO increased, the growth curve inhibition became stronger. H. parasuis cells were damaged severely after treatment with BBO for 4 h, demonstrating plasmolysis and enlarged vacuoles, along with broken cell walls and membranes. Total protein and virulence factor expression in H. parasuis was significantly downregulated by BBO. Taken together, these results indicated a substantial antibacterial effect of BBO on H. parasuis.

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.

Expression profile of porcine scavenger receptor A and its role in bacterial phagocytosis by macrophages

Expression of scavenger receptor A (SRA) in macrophages plays key role in macrophage mediated uptake of microbes. However, little is known about the role of porcine scavenger receptor A (pSRA) in phagocytic function of macrophages in swine species. In this study, polyclonal antibody against pSRA was generated by using recombinant proteins to study expression and function of pSRA. We report broad expression of pSRA in different tissues. In the lungs, pSRA is mainly expressed by alveolar macrophages. Blockade of class A scavenger receptor by fucoidan treatment demonstrates that pSRA has role in bacterial phagocytosis by macrophages. Furthermore, importance of SRA-mediated bacterial phagocytosis has been shown using CHO cell line expressing pSRA. In summary, these findings reveal that pSRA, which is predominantly expressed in alveolar macrophages is likely to be an important receptor mediating recognition and uptake of bacteria in pig lungs.

Prevalence and time trend analysis of antimicrobial resistance in respiratory bacterial pathogens collected from diseased pigs in USA between 2006-2016

Swine respiratory disease complex (SRDC) causes massive economic losses to the swine industry and is a major animal welfare concern. Antimicrobials are mainstay in treatment and control of SRDC. However, there is a lack of data on the prevalence and trends in resistance to antimicrobials in bacterial pathogens associated with SRDC. The objective of this study was to estimate the prevalence and changes in resistance to 13 antimicrobials in swine bacterial pathogens (Streptococcus suis, Pasteurella multocida, Actinobacillus suis and Haemophilus parasuis) in the U.S.A using data collected at University of Minnesota Veterinary Diagnostic Laboratory between 2006 and 2016. For antimicrobials for which breakpoints were available, prevalence of resistance remained below 10% except for tetracycline in S. suis and P. multocida isolates, and these prevalence estimates remained consistently low over the years despite statistical significance (p < .05) in trend analysis. For antimicrobial-bacterial combinations without available breakpoints, the odds of isolates being resistant increased by >10% annually for 7 and 1 antimicrobials in H. parasuis and S. suis isolates respectively, and decreased >10% annually for 4 and 1 antimicrobials in A. suis and H. parasuis isolates, respectively, according to the ordinal regression models. Clinical implications of changes in AMR for A. suis and H. parasuis should be interpreted cautiously due to the lack of interpretive criteria and challenges in antimicrobial susceptibility tests in the case of H. parasuis. Future studies should focus on surveillance of antimicrobial resistance and establishment of standardized susceptibility testing methodologies and interpretive criteria for these animal pathogens of critical importance.

Haemophilus parasuis VtaA2 is involved in adhesion to extracellular proteins

Haemophilus parasuis is part of the microbiota of the upper respiratory tract in swine. However, virulent strains can cause a systemic disease known as Glässer’s disease. Several virulence factors have been described in H. parasuis including the virulence-associated trimeric autotransporters (VtaAs). VtaA2 is up-regulated during infection and is only found in virulent strains. In order to determine its biological function, the vtaA2 gene was cloned with its native promotor region in pACYC184, and the transformed Escherichia coli was used to perform functional in vitro assays. VtaA2 was found to have a role in attachment to plastic, mucin, BSA, fibronectin and collagen. As other VtaAs from H. parasuis, the passenger domain of VtaA2 contains collagen domains. In order to examine the contribution of the collagen repeats to VtaA2 function, a recombinant vtaA2 without the central collagen domains was obtained and named vtaA2OL. VtaA2OL showed similar capacity than VtaA2 to adhere to plastic, mucin, BSA, fibronectin and plasma but a reduced capacity to adhere to collagen, suggesting that the collagen domains of VtaA2 are involved in collagen attachment. No function in cell adhesion and invasion to epithelial alveolar cell line A549 or unspecific binding to primary alveolar macrophages was found. Likewise VtaA2 had no role in serum or phagocytosis resistance. We propose that VtaA2 mediates adherence to the host by binding to the mucin, found in the upper respiratory tract mucus, and to the extracellular matrix proteins, present in the connective tissue of systemic sites, such as the serosa.

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.

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.

Effects of Baicalin on piglet monocytes involving PKC-MAPK signaling pathways induced by Haemophilus parasuis

Background

Haemophilus parasuis (HPS) is the causative agent of Glässer’s disease, characterized by arthritis, fibrinous polyserositis and meningitis, and resulting in worldwide economic losses in the swine industry. Baicalin (BA), a commonly used traditional Chinese medication, has been shown to possess a series of activities, such as anti-bacterial, anti-viral, anti-tumor, anti-oxidant and anti-inflammatory activities. However, whether BA has anti-apoptotic effects following HPS infection is unclear. Here, we investigated the anti-apoptotic effects and mechanisms of BA in HPS-induced apoptosis via the protein kinase C (PKC)–mitogen-activated protein kinase (MAPK) pathway in piglet’s mononuclear phagocytes (PMNP).

Results

Our data demonstrated that HPS could induce reactive oxygen species (ROS) production, arrest the cell cycle and promote apoptosis via the PKC–MAPK signaling pathway in PMNP. Moreover, when BA was administered, we observed a reduction in ROS production, suppression of cleavage of caspase-3 in inducing apoptosis, and inhibition of activation of the PKC–MAPK signaling pathway for down-regulating p-JNK, p-p38, p-ERK, p-PKC-α and PKC-δ in PMNP triggered by HPS.

Conclusions

Our data strongly suggest that BA can reverse the apoptosis initiated by HPS through regulating the PKC–MAPK signaling pathway, which represents a promising therapeutic agent in the treatment of HPS infection.

Integration of pharmacokinetic-pharmacodynamic for dose optimization of doxycycline against Haemophilus parasuis in pigs

The aims of this study were to establish optimal doses of doxycycline (dox) against Haemophilus parasuis on the basis of pharmacokinetic-pharmacodynamic (PK-PD) integration modeling. The infected model was established by intranasal inoculation of organism in pigs and confirmed by clinical signs, blood biochemistry, and microscopic examinations. The recommended dose (20 mg/kg b.w.) was administered in pigs through intramuscular routes for PK studies. The area under the concentration 0- to 24-hr curve (AUC_0-24 ), elimination half-life (T_½ke ), and mean residence time (MRT) of dox in healthy and H. parasuis-infected pigs were 55.51 ± 5.72 versus 57.10 ± 4.89 μg·hr/ml, 8.28 ± 0.91 versus 9.80 ± 2.38 hr, and 8.43 ± 0.27 versus 8.79 ± 0.18 hr, respectively. The minimal inhibitory concentration (MIC) of dox against 40 H. parasuis isolates was conducted through broth microdilution method, the corresponding MIC₅₀ and MIC₉₀ were 0.25 and 1 μg/ml, respectively. The Ex vivo growth inhibition data suggested that dox exhibited a concentration-dependent killing mechanism. Based on the observed AUC_24 hr /MIC values by modeling PK-PD data in H. parasuis-infected pigs, the doses predicted to obtain bacteriostatic, bactericidal, and elimination effects for H. parasuis over 24 hr were 5.25, 8.55, and 10.37 mg/kg for the 50% target attainment rate (TAR), and 7.26, 13.82, and 18.17 mg/kg for 90% TAR, respectively. This study provided a more optimized alternative for clinical use and demonstrated that the dosage 20 mg/kg of dox by intramuscular administration could have an effective bactericidal activity against H. parasuis.

Comparative transcriptomic analysis of porcine peripheral blood reveals differentially expressed genes from the cytokine-cytokine receptor interaction pathway related to health status

While some research has looked into the host genetic response in pigs challenged with specific viruses or bacteria, few studies have explored the expression changes of transcripts in the peripheral blood of sick pigs that may be infected with multiple pathogens on farms. In this study, the architecture of the peripheral blood transcriptome of 64 Duroc sired commercial pigs, including 18 healthy animals at entry to a growing facility (set as a control) and 23 pairs of samples from healthy and sick pen mates, was generated using RNA-Seq technology. In total, 246 differentially expressed genes were identified to be specific to the sick animals. Functional enrichment analysis for those genes revealed that the over-represented gene ontology terms for the biological processes category were exclusively immune activity related. The cytokine-cytokine receptor interaction pathway was significantly enriched. Nine functional genes from this pathway encoding members (as well as their receptors) of the interleukins, chemokines, tumor necrosis factors, colony stimulating factors, activins, and interferons exhibited significant transcriptional alteration in sick animals. Our results suggest a subset of novel marker genes that may be useful candidate genes in the evaluation and prediction of health status in pigs under commercial production conditions.

Antimicrobial Activity and Resistance: Influencing Factors

Rational use of antibiotic is the key approach to improve the antibiotic performance and tackling of the antimicrobial resistance. The efficacy of antimicrobials are influenced by many factors: (1) bacterial status (susceptibility and resistance, tolerance, persistence, biofilm) and inoculum size; (2) antimicrobial concentrations [mutant selection window (MSW) and sub-inhibitory concentration]; (3) host factors (serum effect and impact on gut micro-biota). Additional understandings regarding the linkage between antimicrobial usages, bacterial status and host response offers us new insights and encourage the struggle for the designing of antimicrobial treatment regimens that reaching better clinical outcome and minimizing the emergence of resistance at the same time.

Identification of novel Haemophilus parasuis serovar 5 vaccine candidates using an immunoproteomic approach

Haemophilus parasuis is the aetiological agent of Glässer's disease, which is responsible for cases of fibrinous polyserositis, polyarthritis and meningitis. No vaccine is known that provides cross-protection against all serovars. The identification of novel immunoprotective antigens would undoubtedly contribute to the development of efficient subunit vaccines. In the present study, an immunoproteomic approach was used to analyze secreted proteins of H. parasuis and six proteins with high immunogenicity were identified. Five of them were successfully expressed, and their immunogenicity and protective efficacy were assessed in a mouse challenge model. All five proteins elicited strong humoral antibody and cellular immune responses in mice. They all effectively reduced the growth of H. parasuis in mouse organs and conferred different levels of protection (40-80%) against challenge. IgG subtype analysis revealed that the five proteins induce a bias toward a Th1-type immune response, and a significant increase was observed in the cytokine levels of IL-2, IFN-γ and Th2-specific IL-4 in the culture supernatants of splenocytes isolated from immunized mice. The results suggest that both Th1 and Th2 responses are involved in mediating protection. These data suggest that the five proteins could be potential subunit vaccine candidates for use to prevent H. parasuis infection.

BIOLOGICAL SIGNIFICANCE

Haemophilus parasuis can cause huge financial loss in the swine industry worldwide. There are still no vaccines which can provide cross-protection against all serovars. To address this need, we applied an immunoproteomic approach involving 2-DE, MALDI-TOF/TOF MS and Western-blot to identify the secreted proteins which may be able to provide immunoprotection to this disease. We identified six immunogenic proteins, and the immunogenicity and protective efficacy were validated. This result provides a foundation for developing novel subunit vaccines against Haemophilus parasuis.

Omp16-based vaccine encapsulated by alginate-chitosan microspheres provides significant protection against Haemophilus parasuis in mice

Haemophilus parasuis (H. parasuis) is the etiological agent of swine Glässer's disease, which leads to significant economic loss in swine industry over the world. Subunit vaccine based on outer membrane protein is one of the promising choices to protect pigs against H. parasuis infection despite low immunity efficiency. In this paper, outer membrane protein 16 (Omp16) of H. parasuis encapsulated by alginate-chitosan microspheres as antigen carriers was explored for the first time in a mouse model. Our results showed that the microspheres with Omp16 induced significant higher H. parasuis-specific antibodies, and higher titers of IL-2, IL-4, and IFN-γ than those by Omp16-FIA in treated mice (p<0.05). Moreover, H. parasuis load in the tissues from liver, spleen, and lung of mice immunized with microspheres containing Omp16 was significantly decreased (p<0.05) than that in the same counterpart tissues of control groups. In addition, 80% mice treated with Omp16 and 70% mice with Omp16-FIA were survived after challenged with H. parasuis virulent strain LY02 (serovar 5). Therefore, Omp16-based microsphere vaccine induces both humoral and cellular immune responses and provides promising protection against H. parasuis infection in mice.