Display of porcine epidemic diarrhea virus spike protein B-cell linear epitope on Lactobacillus mucosae G01 S-layer surface induce a robust immunogenicity in mice.

The Porcine epidemic diarrhea virus (PEDV) presents a substantial risk to the domestic pig industry, resulting in extensive and fatal viral diarrhea among piglets. Recognizing the mucosal stimulation triggered by PEDV and harnessing the regulatory impact of lactobacilli on intestinal function, we have developed a lactobacillus-based vaccine that is carefully designed to elicit a strong mucosal immune response. Through bioinformatics analysis, we examined PEDV S proteins to identify B-cell linear epitopes that meet the criteria of being non-toxic, soluble, antigenic, and capable of neutralizing the virus. In this study, a genetically modified strain of Lactobacillus mucosae G01 (L.mucosae G01) was created by utilizing the S layer protein (SLP) as a scaffold for surface presentation. Chimeric immunodominant epitopes with neutralizing activity were incorporated at various sites on SLP. The successful expression of SLP chimeric immunodominant epitope 1 on the surface of L.mucosae G01 was confirmed through indirect immunofluorescence and transmission electron microscopy, revealing the formation of a transparent membrane. The findings demonstrate that the oral administration of L.mucosae G01, which expresses the SLP chimeric immunodominant gene epitope1, induces the production of secreted IgA in the intestine and feces of mice. Additionally, there is an elevation in IgG levels in the serum. Moreover, the levels of cytokines IL-2, IL-4, IFN-γ, and IL-17 are significantly increased compared to the negative control group. These results suggest that L. mucosae G01 has the ability to deliver exogenous antigens and elicit a specific mucosal immune response against PEDV. This investigation presents new possibilities for immunoprophylaxis against PEDV-induced diarrhea.

RPA-CRISPR/Cas12a-Based Detection of Haemophilus parasuis.

Haemophilus parasuis (H. parasuis, HPS) is a prominent pathogenic bacterium in pig production. Its infection leads to widespread fibrinous inflammation in various pig tissues and organs, often in conjunction with various respiratory virus infections, and leads to substantial economic losses in the pig industry. Therefore, the rapid diagnosis of this pathogen is of utmost importance. In this study, we used recombinase polymerase amplification (RPA) and clustered regularly interspaced short palindromic repeats (CRISPR) technology to establish a convenient detection and analysis system for H. parasuis that is fast to detect, easy to implement, and accurate to analyze, known as RPA-CRISPR/Cas12a analysis. The process from sample to results can be completed within 1 h with high sensitivity (0.163 pg/µL of DNA template, p < 0.05), which is 104 -fold higher than the common PCR method. The specificity test results show that the RPA-CRISPR/Cas12a analysis of H. parasuis did not react with other common pig pathogens, including Streptococcus suis type II and IX, Actinobacillus pleuropneumoniae, Escherichia coli, Salmonella, Streptococcus suis, and Staphylococcus aureus (p < 0.0001). The RPA-CRISPR/Cas12a assay was applied to 15 serotypes of H. parasuis clinical samples through crude extraction of nucleic acid by boiling method, and all of the samples were successfully identified. It greatly reduces the time and cost of nucleic acid extraction. Moreover, the method allows results to be visualized with blue light. The accurate and convenient detection method could be incorporated into a portable format as point-of-care (POC) diagnostics detection for H. parasuis at the field level.

Development of a multiplex qRT-PCR assay for the detection of porcine epidemic diarrhea virus, porcine transmissible gastroenteritis virus and porcine Deltacoronavirus.

Currently, porcine coronaviruses are prevalent in pigs, and due to the outbreak of COVID-19, porcine coronaviruses have become a research hotspot. porcine epidemic diarrhea virus (PEDV), Transmissible Gastroenteritis Virus (TGEV), and Porcine Deltacoronavirus (PDCoV) mentioned in this study mainly cause diarrhea in pigs. These viruses cause significant economic losses and pose a potential public health threat. In this study, specific primers and probes were designed according to the M gene of PEDV, the S gene of TGEV, and the M gene of PDCoV, respectively, and TaqMan probe-based multiplex real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was developed for the simultaneous detection of PEDV, TGEV, and PDCoV. This method has high sensitivity and specificity, and the detection limit of each virus can reach 2.95 × 100 copies/µl. An assay of 160 clinical samples from pigs with diarrhea showed that the positive rates of PEDV, TGEV, and PDCoV were 38.13, 1.88, and 5.00%; the coinfection rates of PEDV+TGEV, PEDV+PDCoV, TGEV+PDCoV, PEDV+TGEV+PDCoV were 1.25, 1.25, 0, 0.63%, respectively. The positive coincidence rates of the multiplex qRT-PCR and single-reaction qRT-PCR were 100%. This method is of great significance for clinical monitoring of the porcine enteric diarrhea virus and helps reduce the loss of the breeding industry and control the spread of the disease.

Lactate is useful for the efficient replication of porcine epidemic diarrhea virus in cell culture.

Porcine epidemic diarrhea virus (PEDV) is a deadly pathogen infecting pig herds, and has caused significant economic losses around the world. Vaccination remains the most effective way of keeping the PEDV epidemic under control. Previous studies have shown that the host metabolism has a significant impact on viral replication. In this study, we have demonstrated that two substrates of metabolic pathway, glucose and glutamine, play a key role in PEDV replication. Interestingly, the boosting effect of these compounds toward viral replication appeared to be dose-independent. Furthermore, we found that lactate, which is a downstream metabolite, promotes PEDV replication, even when added in excess to the cell culture medium. Moreover, the role of lactate in promoting PEDV was independent of the genotype of PEDV and the multiplicity of infection (MOI). Our findings suggest that lactate is a promising candidate for use as a cell culture additive for promoting PEDV replication. It could improve the efficiency of vaccine production and provide the basis for designing novel antiviral strategies.

Butyrate limits the replication of porcine epidemic diarrhea virus in intestine epithelial cells by enhancing GPR43-mediated IFN-III production.

Porcine epidemic diarrhea virus (PEDV) is a threat to the health of newborn piglets and has a significant impact on the swine industry. Short-chain fatty acids (SCFAs) are gut microbial metabolites that regulate intestinal function through different mechanisms to enhance the intestinal barrier and immune function. In this study, we aimed to determine whether butyrate displayed a better effect than other SCFAs on limiting PEDV replication in porcine intestinal epithelial cells. Mechanistically, butyrate treatment activated the interferon (IFN) response and interferon-stimulated gene (ISG) expression. Further experiments showed that inhibition of GPR43 (free fatty acid receptor 2) in intestinal epithelial cells increased virus infection and reduced antiviral effects through IFN λ response. Our findings revealed that butyrate exerts its antiviral effects by inducing GPR43-mediated IFN production in intestinal epithelial cells.

A novel linear displacement isothermal amplification with strand displacement probes (LDIA-SD) in a pocket-size device for point-of-care testing of infectious diseases.

Nucleic acid amplification is crucial for disease diagnosis, especially lethal infectious diseases such as COVID-19. Compared with PCR, isothermal amplification methods are advantageous for point-of-care testing (POCT). However, complicated primer design limits their application in detecting some short targets or sequences with abnormal GC content. Herein, we developed a novel linear displacement isothermal amplification (LDIA) method using two pairs of conventional primers and Bacillus stearothermophilus (Bst) DNA polymerase, and reactions could be accelerated by adding an extra primer. Pseudorabies virus gE (high GC content) and Salmonella fimW (low GC content) genes were used to evaluate the LDIA assay. Using strand displacement (SD) probes, a LDIA-SD method was developed to realize probe-based specific detection. Additionally, we incorporated a nucleic acid-free extraction step and a pocket-sized device to realize POCT applications of the LDIA-SD method. The LDIA-SD method has advantages including facile primer design, high sensitivity and specificity, and applicability for POCT, especially for amplification of complex sequences and detection of infectious diseases.

Genomic Characterization of Salmonella enterica serovar Weltevreden Associated with Human Diarrhea.

Salmonella Weltevreden is an emerging pathogen associated with human diarrhea, and knowledge of the genomics and epidemiology of this serovar is still limited. In this study, we performed whole-genome sequencing of 96 S. Weltevreden isolates recovered from diarrheal patients and 62 isolates from food animals in China between 2006 and 2017. Together, with an additional 199 genome sequences of S. Weltevreden published in NCBI, we performed an analysis on all 357 S. Weltevreden genome sequences. Our results demonstrated that the majority of S. Weltevreden from diarrheal patients from China (97.92%, 94/96) and the other regions in the world (94.97%, 189/199) identified in this study were sequence type (ST) 365. The remaining types were ST3771 (n = 3), ST22 (n = 1), ST155 (n = 1), and ST684 (n = 1). In addition, ST365 was also widely recovered from animals, food, and environmental samples in different regions of the world. Phylogenetic analysis and pulsed-field gel electrophoresis (PFGE) revealed that S. Weltevreden from diarrheal patients was closely related to those recovered from food and environmental specimens. We also showed that S. Weltevreden did not exhibit severe antimicrobial resistance profiles, suggesting administering antibiotics is still effective for controlling the agent. Interestingly, we found that S. Weltevreden strains carried a number of virulence factor genes, and a 100.03-kb IncFII(S) type plasmid was widely distributed in S. Weltevreden strains. Elimination of this plasmid decreased the bacterial capacity to infect both Caco-2 cells and C57BL/6 mice, suggesting the importance of this plasmid for bacterial virulence. Our results contribute to the understanding of the epidemiology and virulence of S. Weltevreden. IMPORTANCE Salmonella Weltevreden is a pathogen associated with human diarrheal diseases found across the globe. However, knowledge of the genomics and epidemiology of this pathogen is still limited. In this study, we found S. Weltevreden sequence type (ST) 365 is commonly recovered from diarrheal patients in China and many other regions of the world, and there is no major difference between the Chinese isolates and the global isolates at the phylogenetic level. We also demonstrated that ST365 was widely recovered from animal, food, and environmental samples collected in different, global regions. Importantly, we discovered an IncFII(S) type plasmid commonly carried by S. Weltevreden strains of human, animal, and food origins, and this plasmid is likely to contribute to the bacterial pathogenesis. These findings enhance our understanding of the emergence of S. Weltevreden involved in diarrheal outbreaks and the global spread of S. Weltevreden strains.

Accelerated loop-mediated isothermal amplification method for the rapid detection of Streptococcus suis serotypes 2 and 14 based on single nucleotide polymorphisms.

Streptococcus suis serotypes 2 and 14 are the most prevalent zoonotic strains. The establishment of a sensitive and extremely accurate method for point-of-care testing for Streptococcus suis serotype 2 and 14 strains is highly desirable. In this study, a loop primer probe-introduced loop-mediated isothermal amplification assay was developed to differentiate Streptococcus suis serotypes 2 and 14 based on SNP (single nucleotide polymorphism). The specific fluorescent probes were designed for the SNP site specific for serotype 2 and 14 Streptococcus suis cpsK genes, and the loop primer probe-introduced loop-mediated isothermal amplification (LAMP) assay was developed using the specific cleavage properties of the RNase H2 enzyme. Rapid and efficient LAMP assays were realized through the use of loop forward primers and stem forward primers. The results showed that the amplification reaction can be performed efficiently at 59°C. The results can be real-time detected or judged using a smartphone and a 3D-printed visualization cassette. The sensitivity of the LAMP assay can reach 18.4 CFU within 40 minutes. The detection rate of the assay system was evaluated using 19 clinical samples with suspected Streptococcus suis infection, and the detection rate was consistent with the sequencing method, suggesting that the test is highly practical. The LAMP assay for Streptococcus suis serotypes 2 and 14 established in this study has strong specificity, high sensitivity, and simple operation, while the reaction can be performed at an isothermal temperature and is not dependent on complex instruments or professional operators, making it suitable for field testing.

Proteome Analysis of Outer Membrane Vesicles From a Highly Virulent Strain of Haemophilus parasuis.

Haemophilus parasuis has emerged as an important bacterial pathogen in pig husbandry, as H. parasuis can coinfect pigs with a variety of pathogenic microorganisms and further cause an aggravation of the disease. It is crucial to investigate its pathogenetic mechanism. Gram-negative bacteria naturally secrete outer membrane vesicles (OMVs), and their potent virulence factors play prominent roles that affect the interaction between bacteria and host. Still, the pathogenesis that is associated with the bacterial OMVs has not been well-elucidated. In this study, we investigated the secretion of OMVs from a clinical H. parasuis isolate strain (H45). In addition, we further analyzed the characterization, the comprehensive proteome, and the virulence potential of OMVs. Our data demonstrated that H. parasuis could secrete OMVs into the extracellular milieu during infection. Using liquid chromatography with tandem mass spectrometry (MS/MS) identification and bio-information analysis, we identified 588 different proteins associated with OMVs. Also, we also analyzed the subcellular location and biological function of those proteins. These proteins are mainly involved in immune and iron metabolism. Moreover, we confirmed the pathogenicity of H. parasuis OMVs by observing a strong inflammatory response in J774A.1 and porcine alveolar macrophages. Taken together, our findings suggested that OMVs from H. parasuis were involved in the pathogenesis of this bacterium during infection.

Crosstalk Between Autophagy and the cGAS-STING Signaling Pathway in Type I Interferon Production.

Innate immunity is the front-line defense against infectious microorganisms, including viruses and bacteria. Type I interferons are pleiotropic cytokines that perform antiviral, antiproliferative, and immunomodulatory functions in cells. The cGAS-STING pathway, comprising the main DNA sensor cyclic guanosine monophosphate/adenosine monophosphate synthase (cGAS) and stimulator of IFN genes (STING), is a major pathway that mediates immune reactions and is involved in the strong induction of type I IFN production, which can fight against microbial infections. Autophagy is an evolutionarily conserved degradation process that is required to maintain host health and facilitate capture and elimination of invading pathogens by the immune system. Mounting evidence indicates that autophagy plays an important role in cGAS-STING signaling pathway-mediated type I IFN production. This review briefly summarizes the research progress on how autophagy regulates the cGAS-STING pathway, regulating type I IFN production, with a particular focus on the crosstalk between autophagy and cGAS-STING signaling during infection by pathogenic microorganisms.

Single Multiple Cross Displacement Amplification for Rapid and Real-Time Detection of Porcine Circovirus 3.

Since 2016, a novel porcine circovirus, PCV3, has been infecting pigs, causing significant economic losses to the pig industry. In recent years, the infection rate of PCV3 has been increasing, and thus rapid and accurate detection methods for PCV3 are essential. In this study, we established a novel probe-based single multiple cross displacement amplification (P-S-MCDA) method for PCV3. The method was termed as P-S-MCDA. The P-S-MCDA uses seven primers to amplify the capsid gene, and the assay can be performed at 60°C for 30 min, greatly shortening the reaction time. The results of P-S-MCDA can not only be monitored in real time through fluorescence signals but also be determined by observing the fluorescence of the reaction tubes using a smartphone-based cassette. This method demonstrated good specificity and the same sensitivity as qPCR, with a minimum detection limit of 10 copies. In 139 clinical samples, the coincidence rate with qPCR was 100%. The P-S-MCDA can be widely applied in PCV3 detection in laboratories or in rural areas.

RIPK3-Dependent Necroptosis Limits PRV Replication in PK-15 Cells.

Pigs infected by pseudorabies virus (PRV) display necrotic pathology in multiple organs. The mechanism by which PRV induces cell death is still unclear. Recently, necroptosis was identified as a programmed process dependent on the receptor interacting protein kinase 3 (RIPK3) and mixed lineage kinase-like protein (MLKL). In this study, we demonstrated that PRV induced RIPK3-dependent necroptosis in PK-15 cells. The data showed that PRV infection caused cell death with Propidium Iodide (PI)-positive staining. Transmission electron microscopy analysis indicated plasma membrane disruption in PRV-infected cells. A pan-caspase inhibitor did not prevent PRV-induced necrotic cell death. Western blot analysis indicated that caspase-3 and caspase-8 were not cleaved during PRV infection. Although the transcription of tumor necrosis factor-alpha (TNF-α) was increased by PRV infection, RIPK1 was shown to be not involved in PRV-induced necrotic cell death by use of its specific inhibitor. Further experiments indicated that the phosphorylation of RIPK3 and MLKL was upregulated in PRV-infected cells. Stable shRNA knockdown of RIPK3 or MLKL had a recovery effect on PRV-induced necrotic cell death. Meanwhile, viral titers were enhanced in RIPK3 and MLKL knockdown cells. Hence, we concluded that initiation of necroptosis in host cells plays a limiting role in PRV infection. Considering that necroptosis is an inflammatory form of programmed cell death, our data may be beneficial for understanding the necrotic pathology of pigs infected by PRV.

Competitive activation cross amplification combined with smartphone-based quantification for point-of-care detection of single nucleotide polymorphism.

In this study, we firstly propose a novel smartphone-assisted visualization SNP genotyping method termed competitive activation cross amplification (CACA). The mutation detection strategy depends on the ingenious design of both a start primer and a verification probe with ribonucleotide insertion through competitive combination and perfect matching with the target DNA, Meanwhile, the RNase H2 enzyme was utilized to specifically cleave ribonucleotide insertion and achieve extremely specific dual verification. Simultaneously, the results allow both colorimetric and fluorescence product dual-mode visualization by using self-designed 3D-printed dual function cassette. We validated this novel CACA by analyzing the Salmonella Pullorum rfbS gene at the 237th site, successfully solve the current bottleneck of specific identification and visual detection of this pathogen. The concentration detection limits of the plasmid and genomic DNA were 1500 copies/µL and 3.98 pg/µL, respectively, and as low as the presence of 0.1% mutant-type can be distinguished from 99.9% wild-type. Combined with a powerful hand-warmer, which can provide heating more than 60 °C for 20 h to realize power-free, dual function cassette and smartphone quantitation, our novel CACA platform firstly realizes user-friendly, cost-effective, portable, rapid, and accurate POC detection of SNP.

Comparison of Host Cytokine Response in Piglets Infected With Toxigenic and Non-toxigenic Staphylococcus hyicus.

Staphylococcus hyicus is the most common causative agent of exudative epidermitis (EE) in piglets. Staphylococcus hyicus can be grouped into toxigenic and non-toxigenic strains based on its ability to cause EE in pigs. However, the inflammatory response of piglets infected with toxigenic and non-toxigenic S. hyicus has not been elucidated. In this study, we evaluated the serum cytokine profile in piglets inoculated with toxigenic and non-toxigenic S. hyicus strains and recorded the clinical signs in piglets. Fifteen piglets were divided into three groups (n = 5) and inoculated with a toxigenic strain (ZC-4), a non-toxigenic strain (CF-1), and PBS (control), respectively. The changes in serum levels of cytokines (interleukin [IL]-1ß, IL-4, IL-6, IL-8, IL-10, IL-12, granulocyte-macrophage colony-stimulating factor, interferon-γ, transforming growth factor-ß1, and tumor necrosis factor-α) were evaluated using a cytokine array at 6, 24, 48, and 72 h post inoculation. The results showed that piglets infected with the toxigenic strain exhibited more severe clinical signs and higher mortality than those infected with the non-toxigenic strain. The serum levels of pro-inflammatory cytokine IL-1ß were significantly increased in toxigenic-and non-toxigenic-strain-infected piglets compared to those in the control group (p < 0.05), while the anti-inflammatory cytokine IL-10 was significantly up-regulated only in toxigenic group than in control group (p < 0.05). These results indicated that piglets infected with toxigenic and non-toxigenic S. hyicus showed differential infection status and inflammatory responses. Both toxigenic- and non-toxigenic- S. hyicus infection could induce a pro-inflammatory reaction in piglets. In addition, the toxigenic strain induced a strong anti-inflammatory response in piglets as indicated by the increased serum level of IL-10, which may be associated with the severe clinical signs and increased mortality and may be the key cytokine response responsible for pathogenic mechanisms of S. hyicus.

A one-step closed-tube enzyme-activated blocked probe assay based on SNP for rapid detection of Salmonella Pullorum.

Salmonella enterica serovar Gallinarum biovars Pullorum (S. Pullorum) is an infectious bacterial pathogen in the poultry industry that causes systemic pullorum disease. This disease causes great losses in terms of the clinical production and quality of chicken products in breeding farms. However, an acknowledged usable rapid detection method for its specific identification has not been reported, and it is generally difficult to distinguish from fowl typhoid caused by Salmonella enterica serovar Gallinarum biovars Gallinarum. The development of a specific and rapid detection method for this pathogen is therefore needed. In the present study, we targeted the single-nucleotide mutation position 237 of the S. Pullorum rfbS gene to develop an enzyme-activated blocked probe for its clinical rapid detection. The method displayed robust specificity and reproducibility, and it achieved minimal detection limits of 21 copies/µL of copy number and 4.53 pg/µL of genomic DNA. Compared with traditional identification and PCR methods, this method performed better for the detection of 100 clinical actual samples and without false negative results. The entire process can be accomplished in a 1-step closed-tube operation, overcomes the difficulties currently associated with S. Pullorum detection, and provides a specific and rapid method with broad application potential for SNP detection.

The Colorimetric Isothermal Multiple-Self-Matching-Initiated Amplification Using Cresol Red for Rapid and Sensitive Detection of Porcine Circovirus 3.

In 2016, a novel porcine circovirus (PCV), PCV3, was identified in USA. Subsequently, it was proved to be also epidemic in China, Poland, and Korea. To analyze and control the epidemic situation of PCV3, it is necessary to establish accurate and high-throughput detection methods. In this study, the colorimetric isothermal multiple-self-matching-initiated amplification (IMSA) using cresol red was developed to detect PCV3 for the first time. The reaction can be easily performed by incubating the tube at 63°C for 60 min. By the addition of pH-sensitive indicator dye cresol red, the initial color of the reaction mixture is red. When PCV3 capsid gene DNA was positive in the sample, the color of the reaction mixture changed from red to yellow after the isothermal incubation at 63°C, while the negative control maintained the red color. The colorimetric IMSA displayed good specificity in detecting PCV3, PCV2, and PCV1 and 4 porcine DNA pathogens. Moreover, it has a low and repeatable detection limit of 10 copies, which is consistent with TaqMan-based qPCR, but 10 times more sensitive than PCR. In diagnosing 128 clinical specimens, it not only showed 100% agreement with qPCR but also detected 15 positive results more than PCR. The colorimetric IMSA we offered might be a good choice for PCV3 epidemiological investigation and point-of-care testing.