Purification of recombinant IpaJ to develop an indirect ELISA-based method for detecting Salmonella enterica serovar Pullorum infections in chickens

An enzyme-activated loop primer probe LAMP method based on a new SNP site in the group_17537 gene for rapid on-site detection of Salmonella Pullorum

Pullorum disease (PD) is a widespread disease that causes significant economic losses within the poultry industry of developing countries. An effective strategy for its prevention and control involves the implementation of decontamination procedures utilizing highly specific on-site detection techniques. In this study, a single-nucleotide polymorphism (SNP) site within the group_17537 gene of Salmonella enterica serovar Gallinarum biovars Pullorum (S. Pullorum) was found by using bioinformatics tools. The prevalence of this SNP among 165 strains of S. Pullorum was determined to exceed 96.3 %. The SNP exhibited a specificity rate greater than 99.9 %, with only 0.08 % detected among 2490 non-target Salmonella strains. It can be concluded that this SNP can be employed to distinguish S. Pullorum from other serotypes of Salmonella, specifically Salmonella enterica serovar Enteritidis (S. Enteritidis) and Salmonella enterica serovar Gallinarum biovars Gallinarum (S. Gallinarum). Additionally, an enzyme-activated loop primer probe LAMP (EALP-LAMP) was developed based on this SNP site for the detection of S. Pullorum. This method exhibited excellent specificity and reproducibility, achieving limit of detection of 53.5 copies/µL with plasmid DNA and 0.2 pg/µL with genomic DNA. Moreover, in clinical applications involving 190 chick embryo samples from poultry farms, 24 samples identified as S. Pullorum positive, aligning with results obtained through traditional isolation and quantitative real-time PCR (qPCR) methods. These fingdings highlight the significant potential of this method, which offers accurate, rapid, on-site and visual detection of S. Pullorum.

Salmonella Phage vB_SpuM_X5: A Novel Approach to Reducing Salmonella Biofilms with Implications for Food Safety

Salmonella, a prevalent foodborne pathogen, poses a significant social and economic strain on both food safety and public health. The application of phages in the control of foodborne pathogens represents an emerging research area. In this study, Salmonella pullorum phage vB_SpuM_X5 (phage X5) was isolated from chicken farm sewage samples. The results revealed that phage X5 is a novel Myoviridae phage. Phage X5 has adequate temperature tolerance (28 °C-60 °C), pH stability (4-12), and a broad host range of Salmonella bacteria (87.50% of tested strains). The addition of phage X5 (MOI of 100 and 1000) to milk inoculated with Salmonella reduced the number of Salmonella by 0.72 to 0.93 log10 CFU/mL and 0.66 to 1.06 log10 CFU/mL at 4 °C and 25 °C, respectively. The addition of phage X5 (MOI of 100 and 1000) to chicken breast inoculated with Salmonella reduced bacterial numbers by 1.13 to 2.42 log10 CFU/mL and 0.81 to 1.25 log10 CFU/mL at 4 °C and 25 °C, respectively. Phage X5 has bactericidal activity against Salmonella and can be used as a potential biological bacteriostatic agent to remove mature biofilms of Salmonella or for the prevention and control of Salmonella.

Recombinant Salmonella enterica OmpX protein expression and its potential for serologically diagnosing Salmonella abortion in mares

Background and Aim

Salmonella abortion in mares is caused by Salmonella enterica subspecies enterica serovar abortus equi infection and is characterized by premature (abortion) or non-viable fetus birth. Although all horses are susceptible to infection, the condition is more often clinically manifested in pregnant mares, with most abortions recorded in young females. In addition, nonspecific clinical disease signs and poorly sensitive and effective bacteriological diagnostic methods hinder rapid and reliable infection diagnoses. Immunochemical methods such as enzyme-linked immunosorbent assay (ELISA) and immunochromatography assays can facilitate effective and rapid diagnoses. However, they require highly specific and active antigens and antibodies. This study aimed to generate a recombinant S. enterica outer membrane protein X (OmpX) and evaluate its suitability for serological diagnosis of Salmonella abortion in mares.

Materials and Methods

Outer membrane protein X from the S. enterica antigen was synthesized de novo and expressed in Escherichia coli using the pET28 vector. Transformed E. coli cells were cultured under different conditions to detect recombinant OmpX (rOmpX) expression, and rOmpX purification and refolding were both conducted using metal affinity chromatography. Refolded and purified rOmpX was characterized by western blotting, liquid chromatography with tandem mass spectrometry, and ELISA.

Results

After optimized rOmpX expression, a 23 kDa molecular weight protein was identified. Amino acid sequence analysis using Mascot program suggested that these peptides were the OmpX protein from S. enterica. High specificity and diagnostic efficiency were recorded when rOmpX was used in ELISA against 89 serum samples from aborted and contact mares.

Conclusion

Recombinant outer membrane protein, in comparison to the O antigen, demonstrated better diagnostic characteristics against sera from mares who aborted and contact horses.

Lactobacillus casei protects intestinal mucosa from damage in chicks caused by Salmonella pullorum via regulating immunity and the Wnt signaling pathway and maintaining the abundance of gut microbiota

Dysfunction of the intestinal mucosal barrier of chicks caused by Salmonella pullorum is of great harm to the poultry industry. Probiotics are recognized for their beneficial health-promoting properties, promoting maintenance of bowel epithelial integrity and host immune system homeostasis. Our previous research showed that Lactobacillus casei protects jejunal mucosa from injury in chicks infected with S. pullorum. However, the specific mechanisms underlying its protective properties are still not fully understood. In the present study, we aimed to explore the mechanisms underlying the protective effects of L. casei on the intestinal mucosal barrier of chicks infected with S. pullorum through histological, immunological, and molecular biology methods. The results indicated that L. casei significantly reduced the diarrhea rate, increased the daily weight gain, and maintained normal levels of IgA, IgM, and IgG in the serum of chicks infected with S. pullorum. Furthermore, we found that L. casei markedly improved the immunity of gut mucosa by regulating cytokine and chemokine receptor balance, elevating the number of intraepithelial lymphocytes, and hence effectively restraining bowel inflammation. Strikingly, feeding of infected chicks with L. casei notably boosted interleukin-22 expression to activate the Wingless-Int pathway, moderated diamine oxidase and D-lactic acid levels, diminished the generation of myosin light chain kinase, and expanded tight junction protein levels (Zonulin-1 and Claudin-1), strengthening the function of the gut mucosal epithelium. In addition, experiments using 16S rDNA sequencing also demonstrated that L. casei immensely weakened the adhesion of S. pullorum, mainly manifesting as improved diversity of the intestinal microbiota in the V4 area of infected chicks. Taken together, these results show that the application of L. casei may be a good strategy to regulate the intestinal inflammatory response of chicks infected with S. pullorum, providing new perspectives in producing antibiotic substitutes in poultry farms.

Self-made Salmonella Pullorum agglutination antigen development and its potential practical application

Pullorum disease caused by Salmonella Pullorum is one of the most important infectious diseases in the poultry industry worldwide, which leads to serious economic losses in many developing countries because of its high mortality rate in young chicks. The traditional slide agglutination test with low cost, fast reaction, and on-site detection has been widely used in the diagnosis of Pullorum disease. However, in practice, the test performance is with the disadvantages of false positive results and unstable detection results. In this paper, we developed self-made agglutination antigens prepared by local isolates in the poultry farm and compare the detection performance with commercial agglutination antigens (China Institute of Veterinary Drug Control) and Group D Salmonella ELISA kit (BioChek UK Ltd). The results of detecting 200 serum samples indicated that the consistency of commercial agglutination antigen detecting in 2 times was only 79.5%. Using the ELISA kit as the reference method, the commercial agglutination antigen detecting results of the Kappa test were only moderately consistent (0.58 ∼ 0.59). Meanwhile, positive and total coincidence rates of the self-made agglutination antigen test with more reliable repeat could reach 97.4 and 88%, respectively, and the result of Kappa test was highly consistent (0.75). The Receiver Operating Characteristic curve analysis clarified that the area under the receiver-operating-characteristic curve values of self-made and commercial agglutination antigen tests could reach 0.861 and 0.804, respectively. These results were coincident when detecting known positive serum from the infected chickens. It's worth mentioning that the visible positive reaction of self-made agglutination antigen test appeared faster and stronger than commercial antigen test. In conclusion, self-made Salmonella Pullorum agglutination antigen developed in this study was much better than commercial agglutination antigen and is expected to be a valuable tool in the diagnosis of the epidemiology of Salmonella Pullorum.

Application of Monoclonal Antibodies Developed Against the IpaJ Protein for Detection of Chickens Infected With Salmonella enterica Serovar Pullorum Using Competitive ELISA

Pullorum disease remains an epidemic in the poultry industry in China. The causing pathogen is a host-restricted Salmonella enterica serovar Pullorum, which can spread through both horizontal and vertical transmissions. To eradicate the pullorum disease from poultry farms, it is necessary to specifically monitor the prevalence of the bacterial infection in adult chicks. In this study, we constructed a new competitive ELISA method based on the development of monoclonal antibodies (MAbs) against a specific immunogen of S. Pullorum, IpaJ protein. In total, eight MAbs against IpaJ were prepared using the purified recombinant His-IpaJ protein as the immunogen. Characterization of the eight MAbs demonstrated that 4G5 can be used as the competitive antibody in ELISA. A competitive ELISA was subsequently developed using purified MBP-IpaJ as the capture (0.5 μg/ml) and the HRP-labeled 4G5 (0.14 μg/ml) as the competitive antibody, respectively. A specificity test demonstrated that the ELISA assay can differentiate antisera of S. Pullorum-infected chickens from that of S. Gallinarum and S. Enteritidis. Furthermore, 4 out of 200 clinical antisera collected from a poultry farm were detected to be S. Pulloram positive using this method. The plate agglutination test (PAT) and the previously established indirect ELISA confirmed that these positive antisera reacted specifically with S. Pullorum. We propose that the established competitive ELISA assay based on MAb against IpaJ protein, is a novel and quick method that can detect S. Pullroum infection in the poultry industry.

Instrument-Free and Visual Detection of Salmonella Based on Magnetic Nanoparticles and an Antibody Probe Immunosensor

Salmonella, a common foodborne pathogen, causes many cases of foodborne illness and poses a threat to public health worldwide. Immunological detection systems can be combined with nanoparticles to develop sensitive and portable detection technologies for timely screening of Salmonella infections. Here, we developed an antibody-probe-based immuno-N-hydroxysuccinimide (NHS) bead (AIB) system to detect Salmonella. After adding the antibody probe, Salmonella accumulated in the samples on the surfaces of the immuno-NHS beads (INBs), forming a sandwich structure (INB–Salmonella–probes). We demonstrated the utility of our AIB diagnostic system for detecting Salmonella in water, milk, and eggs, with a sensitivity of 9 CFU mL⁻¹ in less than 50 min. The AIB diagnostic system exhibits highly specific detection and no cross-reaction with other similar microbial strains. With no specialized equipment or technical requirements, the AIB diagnostic method can be used for visual, rapid, and point-of-care detection of Salmonella.