Elucidating the biological characteristics and pathogenicity of the highly virulent G2a porcine epidemic diarrhea virus.

Since the large-scale outbreak of porcine epidemic diarrhoea (PED) in 2010, caused by the genotype 2 (G2) variant of the porcine epidemic diarrhoea virus (PEDV), pig farms in China, even those vaccinated with the G2b vaccine, have experienced infections from the G2a variant, leading to significant economic losses. This study successfully isolated the G2a strain DY2020 from positive small intestine contents (SICs) by blind passage on Vero cells for four generations. The SICs were taken from Daye, Hubei Province, China. The biological characteristics were identified by indirect immunofluorescence assay (IFA) and transmission electron microscopy (TEM). The growth kinetics of the strain on Vero cells were detected by TCID50, and the virus titre could reach 107.35 TCID50 ml-1 (SD: 5.07×106). The pathogenicity towards colostrum-deprived piglets was conducted by assessing faecal viral shedding, morphometric analysis of intestinal lesions, and immunohistochemical staining. The results showed that DY2020 was highly virulent to colostrum-deprived piglets, with severe watery diarrhoea and other clinical symptoms appeared at 6 h post-infection (h p.i.), and all died within 30 h. Pathological tissue examination results showed that the lesions mainly occurred in the intestines of piglets, causing pathological changes such as shortening of intestinal villi. In summary, the discovery of the G2a strain DY2020 in this study is of great significance for understanding Hubei PEDV and provides an important theoretical basis for the development of new efficient PEDV vaccines.

Isolation, identification and characteristics of Bibersteinia trehalosi from goat.

A conditionally pathogenic bacterium called Bibersteinia trehalosi inhabits the upper respiratory tract of ruminants and is becoming a significant cause of pneumonia, especially in goats. In this study, we identified a gram-negative bacteria strain isolated from dead goat's lungs, which was named M01. By integrating the outcomes of its morphological and biochemical characterization with the investigation of the 16S rRNA gene sequence analysis, the isolate was identified as B. trehalosi. Based on antibiotic susceptibility tests, the isolate was shown to be resistant to ß-lactams, tetracyclines, and amphenicols. Its genome was discovered to comprise 2115 encoded genes and a circular chromosome measuring 2,345,568 bp using whole genome sequencing. Annotation of the VFBD database revealed that isolate M01 had four virulence genes encoding three virulence factors. The CARD database revealed that its genome has two antibiotic-resistance genes. Based on pathogenicity testing, isolate M01 was highly pathogenic to mice, primarily causing pneumonia, with an LD50 of 1.31 × 107 CFU/ml. Moreover, histopathology showed loss of alveolar structure and infiltration of lung inflammatory cells. Hence, the current study could provide sufficient information for prevention and control strategies for future epidemics of B. trehalosi in goat species.

Mutations in troABCD against Copper Overload in a copA Mutant of Streptococcus suis.

Streptococcus suis is a major swine pathogen that is increasingly recognized as a porcine zoonotic pathogen that threatens the health of both pigs and humans. Metal homeostasis plays a critical role during the process of bacterial infection. In this study, RNA sequencing was used to identify potential candidate genes involved in the maintenance of intracellular copper homeostasis. CopA was identified as the primary copper exporter in S. suis. The copA deletion mutant strain was found to be more sensitive to copper and accumulated more intracellular copper than the wild-type (WT) parent strain. In addition, adding manganese increased the ability of S. suis to resist copper, and the manganese transporter, TroABCD, was involved in tolerance to copper. The copA deletion mutant strain accumulated less copper when supplemented with manganese. Furthermore, when cultured with copper, the double deletion mutant (ΔcopAΔtroA) exhibited improved growth compared to the copA deletion mutant strain. In addition, the double deletion mutant (ΔcopAΔtroA) accumulated less copper than the copA deletion mutant strain. These data were consistent with a model wherein defective TroABCD resulted in decreased cellular copper accumulation and protected the strain against copper poisoning. IMPORTANCE Metal homeostasis plays a critical role during the process of bacterial infection. We identified three important potential candidate genes involved in maintenance of intracellular copper homeostasis. CopA was demonstrated to be the main copper exporter in Streptococcus suis, and manganese increased the tolerance of S. suis to copper. The double deletion mutant (ΔcopAΔtroA) improved growth ability over the copA deletion mutant strain in the presence of high concentrations of copper and accumulated less copper. These findings are consistent with a model wherein defective TroABCD resulted in decreased cellular accumulation of copper and protected the strain against copper poisoning.

Tea Polyphenols Protects Tracheal Epithelial Tight Junctions in Lung during Actinobacillus pleuropneumoniae Infection via Suppressing TLR-4/MAPK/PKC-MLCK Signaling.

Actinobacillus pleuropneumoniae (APP) is the causative pathogen of porcine pleuropneumonia, a highly contagious respiratory disease in the pig industry. The increasingly severe antimicrobial resistance in APP urgently requires novel antibacterial alternatives for the treatment of APP infection. In this study, we investigated the effect of tea polyphenols (TP) against APP. MIC and MBC of TP showed significant inhibitory effects on bacteria growth and caused cellular damage to APP. Furthermore, TP decreased adherent activity of APP to the newborn pig tracheal epithelial cells (NPTr) and the destruction of the tight adherence junction proteins ß-catenin and occludin. Moreover, TP improved the survival rate of APP infected mice but also attenuated the release of the inflammation-related cytokines IL-6, IL-8, and TNF-α. TP inhibited activation of the TLR/MAPK/PKC-MLCK signaling for down-regulated TLR-2, TLR4, p-JNK, p-p38, p-PKC-α, and MLCK in cells triggered by APP. Collectively, our data suggest that TP represents a promising therapeutic agent in the treatment of APP infection.

Theaflavin Ameliorates Streptococcus suis-Induced Infection In Vitro and In Vivo.

Streptococcus suis (S. suis) is one of the most important zoonotic pathogens that threaten the lives of pigs and humans. Even worse, the increasingly severe antimicrobial resistance in S. suis is becoming a global issue. Therefore, there is an urgent need to discover novel antibacterial alternatives for the treatment of S. suis infection. In this study, we investigated theaflavin (TF1), a benzoaphenone compound extracted from black tea, as a potential phytochemical compound against S. suis. TF1 at MIC showed significant inhibitory effects on S. suis growth, hemolytic activity, and biofilm formation, and caused damage to S. suis cells in vitro. TF1 had no cytotoxicity and decreased adherent activity of S. suis to the epithelial cell Nptr. Furthermore, TF1 not only improved the survival rate of S. suis-infected mice but also reduced the bacterial load and the production of IL-6 and TNF-α. A hemolysis test revealed the direct interaction between TF1 and Sly, while molecular docking showed TF1 had a good binding activity with the Glu198, Lys190, Asp111, and Ser374 of Sly. Moreover, virulence-related genes were downregulated in the TF1-treated group. Collectively, our findings suggested that TF1 can be used as a potential inhibitor for treating S. suis infection in view of its antibacterial and antihemolytic activity.

PerR-Regulated Manganese Import Contributes to Oxidative Stress Defense in Streptococcus suis.

Streptococcus suis has been increasingly recognized as a porcine zoonotic pathogen that threatens the health of both pigs and humans. Metal homeostasis plays a critical role in the antioxidative capability of bacteria, thus facilitating the escape of pathogenic species from the innate immunity systems of hosts. Here, we revealed that manganese increased the ability of S. suis to resist oxidative stress. RNA sequencing was used to identify potential candidate genes involved in the maintenance of intracellular manganese homeostasis. Four genes, termed troABCD, were identified by NCBI BLASTp analysis. The troA, troB, troC, and troD deletion mutant strains exhibited decreased intracellular manganese content and tolerance to H2O2 compared to the wild-type strain. Thus, troABCD were determined to be involved in manganese uptake and played an important role in H2O2 tolerance in S. suis. Furthermore, the inactivation of perR increased the survival of H2O2-pulsed S. suis 2.18-fold and elevated the intracellular manganese content. H2O2-pulsed S. suis and perR deletion mutants upregulated troABCD. This finding suggested that H2O2 released the suppression of troABCD by perR. In addition, an electrophoretic mobility shift assay (EMSA) showed that PerR at 500 ng binds to the troABCD promoter, indicating that troABCD were directly regulated by PerR. In conclusion, this study revealed that manganese increases tolerance to H2O2 by upregulating the expression of troABCD. Moreover, PerR-regulated Mn import in S. suis and increased the tolerance of S. suis to oxidative stress by regulating troABCD. IMPORTANCE During infection, it is extremely important for bacteria to defend against oxidative stress. While manganese plays an important role in this process, its role is unclear in S. suis. Here, we demonstrated that manganese increased S. suis tolerance to oxidative stress. Four manganese ABC transporter genes, troABCD, were identified. Oxidative stress increased the content of manganese in the cell. Furthermore, PerR increased the tolerance to oxidative stress of S. suis by regulating troABCD. Manganese played an important role in bacterial defense against oxidative stress. These findings provide novel insight into the mechanism by which S. suis resists oxidative stress and approaches to inhibit bacterial infection by limiting manganese intake.

The VraSR two-component signal transduction system contributes to the damage of blood-brain barrier during Streptococcus suis meningitis.

Streptococcus suis (S. suis) is an important zoonotic pathogen that can cause high morbidity and mortality in both humans and swine. As the most important life-threatening infection of the central nervous system (CNS), meningitis is an important syndrome of S. suis infection. The vancomycin resistance associated sensor/regulator (VraSR) is a critical two-component signal transduction system that affects the ability of S. suis to resist the host innate immune system and promotes its ability to adhere to brain microvascular endothelial cells (BMECs). Prior work also found mice infected with ΔvraSR had no obvious neurological symptoms, unlike mice infected with wild-type SC19. Whether and how VraSR participates in the development of S. suis meningitis remains unknown. Here, we found ΔvraSR-infected mice did not show obvious meningitis, compared with wild-type SC19-infected mice. Moreover, the proinflammatory cytokines and chemokines in serum and brains of ΔvraSR-infected mice, including IL-6, TNF-α, MCP-1 and IFN-γ, were significantly lower than wild-type infected group. Besides, blood-brain barrier (BBB) permeability also confirmed that the mutant had lower ability to disrupt BBB. Furthermore, in vivo and in vitro experiments showed that SC19 could increase BBB permeability by downregulating tight junction (TJ) proteins such as ZO-1, ß-Catenin, Occludin, and Clauidn-5, compared with mutant ΔvraSR. These findings provide new insight into the influence of S. suis VraSR on BBB disruption during the pathogenic process of streptococcal meningitis, thereby offering potential targets for future preventative and therapeutic strategies against this disease.

Green tea polyphenols inhibit growth, pathogenicity and metabolomics profiles of Streptococcus suis.

Streptococcus suis (SS) is an important pathogen in pigs and can also cause severe infection in humans. Currently, more and more drug resistance is reported, resulting in the search for new drugs being needed urgently. Green tea polyphenols (GTP) was reported to inhibit many bacteria. However, SS response to GTP has not been studied before. In this report, the effect of GTP on growth, cell integrity, pathogenicity and metabolic pathway of SS was examined. The GTP inhibited growth, led to cellular damage, and attenuated pathogenicity of SS. Finally, GTP affected many important metabolic pathways of SS, such as ABC transporters, pyrimidine metabolism, protein digestion and absorption. The results provide new insight into the prevention and control of SS infection.

Expression profile of long non-coding RNAs in porcine lymphnode response to porcine circovirus type 2 infection.

Porcine circovirus type 2 (PCV2) can cause various clinical diseases in pigs, resulting in huge losses for the pig farms all over the world. In order to develop a new strategy to control PCV2, it is essential to understand its mechanisms firstly, especially PCV2 interferes with the host's innate immunity. In the present study, lncRNA and mRNA expression profiles in porcine lymphnode response to PCV2 infection were deeply sequenced and analyzed. 3271 novel lncRNAs were identified in all. 1898 mRNAs and 282 lncRNAs showed differential expression between control and PCV2-infected groups. The bioinformatics analysis including lncRNA-mRNA co-expression network construction, as well as GO and KEGG pathway analysis focused on the DEGs was carried out. The results indicated that lncRNAs might participate in PCV2 infection-induced the pathogenesis of immunosuppression through regulating the host's immune responses, biological regulation, response to stimulus, cellular component organization or biogenesis and metabolism. And these differentially expressed lncRNAs might play important roles in response to PCV2 infection in the host's innate immune system. These findings provided a large-scale survey of dysregulated lncRNAs after PCV2 infection, especially the lncRNAs responded to host's innate immune within the lymphnode. This study will provide a novel insight into the lncRNAs' functions and the possible immunosuppressive mechanism induced by PCV2 infection. However, further research will be required to verify the characteristic function of the dysregulated lncRNAs.

Rapid and simultaneous detection of Japanese encephalitis virus by real-time nucleic acid sequence-based amplification.

Japaneses encephalitis (JE) is most common zoonoses caused by Japanese encephalitis virus (JEV) with a high mortality and disability rate. To take timely preventive and control measures, early and rapid detection of JE RNA is necessary. But due to characteristic brief and low viraemia, JE RNA detection remains challenging. In this study, a real-time nucleic acid sequence-based amplification (RT-NASBA) was developed for rapid and simultaneous detection of JEV. Four pairs of primer were designed using a multiple genome alignment of all JEV strains from GenBank. NASBA assay established and optimal reaction conditions were confirmed by using primers and probe on ns1 gene of JEV. The specificity and sensitivity of the assay were compared with RT-PCR by using serial RNA and virus cultivation dilutions. The results showed that JEV RT-NASBA assay was established, and robust signals could be observed in 10 min with high specificity. The limit of dectetion of RT-NASBA was 6 copies per reaction. The assay was thus 100 to 1, 000 times more sensitive than RT-PCR. The cross-reaction was performed with other porcine pathogens, and negative amplification results indicated the high specificity of this method. The novel JEV RT-NASBA assay could be used as an efficient molecular biology tool to diagnose JEV, which would facilitate the surveillance of reproductive failure disease in swine and would be beneficial for public health security.

Tea polyphenols inhibit the growth and virulence of ETEC K88.

Diarrhea caused by Enterotoxigenic Escherichia coli (ETEC) causes high levels of morbidity and mortality in neonatal piglets. Owing to the abuse of antibiotics and emergence of drug resistance, antibiotics are no longer considered only beneficial, but also potentially harmful drugs. Supplements that can inhibit the growth of bacteria are expected to replace antibiotics. Tea polyphenols have numerous important biological functions, including antibacterial, antiviral, antioxidative, anti-inflammatory, and antihypertensive effects. We investigated the role of tea polyphenols in ETEC K88 infection using a mouse model. Pretreating with tea polyphenols attenuated the symptoms induced by ETEC K88. Furthermore, in a cell adherence assay, tea polyphenols inhibited ETEC K88 adherence to IPEC-J2 cells. When cells were infected with ETEC K88, mRNA and protein levels of claudin-1 were significantly decreased compared with those of control cells. However, when cells were pretreated with tea polyphenols, claudin-1 mRNA and protein levels were higher than those in cells without pretreatment upon cell infection with ETEC K88. TLR2 mRNA levels were also higher following cell infection with ETEC K88 when cells were pretreated with tea polyphenols. These data revealed that tea polyphenols could increase the barrier integrity of IPEC-J2 cells by upregulating expression of claudin-1 through activation of TLR2. Tea polyphenols had beneficial effects on epithelial barrier function. Therefore, tea polyphenols could be used as a novel strategy to control and treat pig infections caused by ETEC K88.

Biological characteristics and genetic evolutionary analysis of emerging pathogenic Bacillus cereus isolated from Père David's deer (Elaphurus davidianus).

Bacillus cereus (B. cereus) is widely distributed in the environment. It is one of the most common opportunistic food-borne pathogens associated with food poisoning, not only being majorly reported to cause fatal infections of the gastrointestinal tract, but also responsible for abdominal distress and vomiting. The current study was undertaken to evaluate the biological characteristics and the genetic evolution of B. cereus isolated from infected organs of dead Elaphurus davidianus (E. davidianus). B. cereus was characterized through antibiotic sensitivity tests, mouse lethality assay, whole genome sequencing analysis, and genome annotation. The results revealed that the isolated B. cereus strain was highly resistant to rifampicin, lincomycin, sulfamethoxazole, erythromycin, and ampicillin, with a high pathogenicity phenotype. KEGG annotation revealed that "metabolic pathways" had the largest number of unigenes, followed by "biosynthesis of secondary metabolites" and "biosynthesis of antibiotics". GO analysis resulted in 8039 unigenes categorized. Meanwhile, 54,779 unigenes were annotated and grouped into 23 categories based on COG functional classifications. Moreover, one gene (codY) was found to be related to the host in conformity with the analysis done on PHI-base. Other tests led to the identification of 16 B. cereus virulence factor genes and five resistance types, with potential resistance against bacitracin, penicillin, and fosfomycin. We isolated a highly drug-resistant and pathogenic B. cereus strain from E. davidianus, showing that a variety of antimicrobial drugs should be avoided in clinical treatments. Furthermore, to the best of our knowledge, this is the first study to report whole genome sequencing of a emergence of food-borne B. cereus strain isolated from E. davidianus deer; it will be helpful to extensively investigate the genetic and molecular mechanisms of drug resistance and pathogenesis about B. cereus in both humans and animals.

Calcium-Sensing Receptor Arbitrates Hypoxia-Induced Proliferation of Pulmonary Artery Smooth Muscle Cells via the G Protein-PLC-IP3 Pathway.

Pulmonary arterial hypertension (PAH), also known as broilers ascites syndrome, is characterized by hypoxia, pulmonary artery pressure, and right heart failure. However, less information is available about the molecular mechanisms of PAH. We evaluated the mediation of calcium-sensing receptor by inducing hypoxia for the possible proliferation of pulmonary artery smooth muscle cells via the G protein pathway. For this purpose, we used an in vitro trial of chicken cell culture and confirmed our results by using immunohistochemistry, immunofluorescence staining, quantitative real-time polymerase chain reaction assay, and Western blotting analysis. Our results showed that the mRNA and protein expression levels of calcium-sensing receptor (CaSR) were significantly upregulated in cells when co-incubated with CaCl2. However, the levels of mRNA and protein were obviously decreased when supplemented with blocking agents (NiCl2, 2-APB, and D609). Furthermore, the experimentally induced hypoxia also upregulated the expression of CaSR gene as compared to CaSR gene expression in control cells. Together, these results indicate that hypoxia plays an important role in the expression of CaSR gene in pulmonary artery smooth muscle cells and reveals new targets for the CaSR excited hypothesis to prevent and control PAH in chickens.

Surface proteins mhp390 (P68) contributes to cilium adherence and mediates inflammation and apoptosis in Mycoplasma hyopneumoniae.

Mycoplasma hyopneumoniae is the causative agent of porcine enzootic pneumonia (EP) and responsible for major economic losses in global swine industry. After colonization of the respiratory epithelium, M. hyopneumoniae elicits a general mucociliary clearance loss, prolonged inflammatory response, host immunosuppression and secondary infections. Until now, the pathogenesis of M. hyopneumoniae is not completely elucidated. This present study explores the pathogenicity of mhp390 (P68, a membrane-associated lipoprotein) by elucidating its multiple functions. Microtitrer plate adherence assay demonstrated that mhp390 is a new cilia adhesin that plays an important role in binding to swine tracheal cilia. Notably, mhp390 could induce significant apoptosis of lymphocytes and monocytes from peripheral blood mononuclear cells (PBMCs), as well as primary alveolar macrophages (PAMs), which might weaken the host immune response. In addition, mhp390 contributes to the production of proinflammatory cytokines, at least partially, via the release of IL-1ß and TNF-α. To the best of our knowledge, this is the first report of the multiple functions of M. hyopneumoniae mhp390, which may supplement known virulence genes and further develop our understanding of the pathogenicity of M. hyopneumoniae.

Binding of Fibronectin to SsPepO Facilitates the Development of Streptococcus suis Meningitis.

Background: SsPepO is an important virulence in Streptococcus suis. Methods: In this study, we showed that SsPepO contributes to the human fibronectin-mediated adherence ability of S. suis to human brain microvascular endothelial cells. Results: The addition of an antifibronectin antibody or an arginine-glycine-aspartic acid peptide that blocks fibronectin binding to integrins significantly reduced adherence of the wild-type but not the SspepO mutant strain, indicating the importance of the SsPepO-fibronectin-integrin interaction for S. suis cellular adherence. Conclusions: By analyzing Evans blue extravasation in vivo, we showed that the interaction between SsPepO and human fibronectin significantly increased permeability of the blood-brain barrier. Furthermore, the SspepO mutant caused lower bacterial loads in the brain than wild-type S. suis in models of meningitis. These data demonstrate that SsPepO is a fibronectin-binding protein, which plays a contributing role in the development of S. suis meningitis.

Development of sandwich Enzyme-Linked Immunosorbent Assay for the detection of porcine epidemic diarrhea virus in fecal samples.

Porcine epidemic diarrhea virus (PEDV) causes acute diarrhea and dehydration in new-born piglets with subsequent economic losses to swine industry. In the current study, gene encoding of 381aa-792aa spike protein (S1) with the main epitope relative to virus neutralization of PEDV was amplified by RT-PCR and inserted into vector pET-30A(+). The plasmid was transferred into Escherichia coli BL21 (DE3). Meanwhile, recombinant protein expression was induced by isopropy1-ß-galactopyranoside (IPTG). After denaturation and renaturation of inclusion bodies, the S1 protein was obtained by using purified recombinant S1 protein in immunized female BALB/c mice. Monoclonal antibodies (MAb) against S1 protein, named 4C7 by hybridoma technique were gained successfully. The result showed that MAb can specifically respond to S1 protein and PEDV via ELISA, Western bolt and immunofluorescence assay methods. A sandwich ELISA (S-ELISA) was established by using the captured monoclonal antibodies 4C7. The sensitivity and specificity were compared between S-ELISA and RT-PCR, which showed similar sensitivity and specificity. This work indicated that S-ELISA would be a significant tool alongside a specific diagnostic reagent for PEDV in future.

The 1910HK/RR two-component system is essential for the virulence of Streptococcus suis serotype 2.

Streptococcus suis serotype 2 is a major zoonotic pathogen, and the two-component system plays an important role in bacterial pathogenesis. The present study targeted the 1910HK/RR two-component system of S. suis 2. A 1910HK/RR deletion mutant (Δ1910HK/RR) and the corresponding complementation strain (CΔ1910HK/RR) were constructed in S. suis 2 strain 05ZYH33. 1910HK/RR deletion had no effect on S. suis 2 growth, but significantly inhibited the adherence and invasion of S. suis 2 to HEp-2 cells. Analysis of the role of 1910HK/RR in murine and pig infection models demonstrated that 1910HK/RR played a distinct role in the virulence of S. suis 2. In addition, deletion of 1910HK/RR significantly impaired the survival of 05ZYH33 in human blood. These data provided important insights into the pathogenesis of S. suis 2.

Advancement in the Antigenic Epitopes and Vaccine Adjuvants of African Swine Fever Virus.

African swine fever virus (ASFV), a highly virulent double-stranded DNA virus, poses a significant threat to global pig farming, with mortality rates in domestic pigs reaching up to 100%. Originating in Kenya in 1921, ASFV has since proliferated to Western Europe, Latin America, Eastern Europe, and most recently China in 2018, resulting in substantial global agricultural losses. Antigenic epitopes, recognized by the immune system's T cells and B cells, are pivotal in antiviral immune responses. The identification and characterization of these antigenic epitopes can offer invaluable insights into the immune response against ASFV and aid in the development of innovative immunotherapeutic strategies. Vaccine adjuvants, substances that amplify the body's specific immune response to antigens, also play a crucial role. This review provides an overview of the progress in studying T/B-cell epitopes in ASFV proteins and ASFV vaccine adjuvants, highlighting their role in the immune response and potential use in new vaccine development.

Porcine circovirus type 2 ORF5 induces an inflammatory response by up-regulating miR-21 levels through targeting nuclear ssc-miR-30d.

Porcine circovirus type 2 (PCV2) infection leads to multi-system inflammation in pigs, and this effect can be achieved by upregulating host miR-21. The underlying mechanism of miR-21 regulates PCV2-induced inflammation is already known, however, how PCV2 regulates miR-21 levels and function using both autonomic and host factors remains to be further revealed. Here we present the first evidence that PCV2 ORF5 induces an inflammatory response by up-regulating miR-21 level through targeting nuclear miR-30d. In this study, we found that overexpression of ORF5 significantly increased miR-21 level and promoted the expression of inflammatory cytokines and activation of the NF-κB pathway, while ORF5 mutation had the opposite effect. Moreover, the differential expression of miR-21 could significantly change the pro-inflammatory effect of ORF5, indicating that ORF5 promotes inflammatory response by up-regulating miR-21. Bioinformatics analysis and clinical detection found that nuclear miR-30d was significantly down-regulated after ORF5 overexpression and PCV2 infection, and targeted pri-miR-21 and PCV2 ORF5. Functionally, we found that miR-30d inhibited the levels of miR-21 and inflammatory cytokines in cells. Mechanistically, we demonstrated that ORF5 inhibits miR-30d expression levels through direct binding but not via the circRNA pathway, and miR-30d inhibits miR-21 levels by targeting pri-miR-21. In summary, the present study revealed the molecular mechanism of ORF5 upregulation of miR-21, further refined the molecular chain of PCV2-induced inflammatory response and elucidated the role of miRNAs in it.

The cAMP receptor protein gene contributes to growth, stress resistance, and colonization of Actinobacillus pleuropneumoniae.

Porcine infectious pleuropneumonia (PCP) is a severe disease of porcine caused by Actinobacillus pleuropneumoniae (APP). The spread of PCP remains a threat to the porcine farms and has been known to cause severe economic losses. The cAMP receptor protein (CRP) serves as a pivotal player in helping bacteria adapt to shifts in their environment, particularly when facing the challenges posed by bacterial infections. In this study, we investigated the role of CRP in APP. Our results revealed that crp mutant (Δcrp) strains were more sensitive to acidic and osmotic stress resistance and had lower biofilm formation ability than wild-type (WT) strains. Furthermore, the Δcrp strains showed deficiencies in anti-phagocytosis, adhesion, and invasion upon interaction with host cells. Mice infected with the Δcrp strains demonstrated reduced bacterial loads in their lungs compared to those infected with the WT strains. This study reveals the pivotal role of crp gene expression in regulating pleuropneumonia growth, stress resistance, iron utilization, biofilm formation, phagocytosis, adhesion, invasion and colonization. Our discoveries offer novel perspectives on understanding the development and progression of APP infections.