A promising detection candidate for flagellated Salmonella spp

Development and application of a competitive ELISA for the detection of antibodies against Salmonella Abortusequi in equids

The high abortion rate associated with Salmonella Abortusequi (S. Abortusequi) infection in equids has re-emerged over the past 10 years and has caused serious economic losses to China. Our previous studies showed that the flagellin FljB gene could distinguish S. Abortusequi from most Salmonella serotypes. In this study, the flagellin antigen was used to develop a competitive enzyme-linked immunosorbent assay (cELISA) that could be used to detect both horse and donkey serum samples using a monoclonal antibody (MAb) that was found to bind to FljB. A cELISA was established using the purified MAb coating of the plate and incubation of the mixture of horseradish peroxidase (HRP)-conjugated FljB antigen with the undiluted serum sample. The performance of the cELISA and the tube agglutination test (TAT) assay was compared with respect to sensitivity and specificity, by testing a panel containing 660 S. Abortusequi-positive and 515 S. Abortusequi-negative serum samples, all of which had been characterized by Western blotting. Receiver operator characteristic (ROC) analyses were performed to determine the cutoff value and estimate the detection specificity (Sp) and sensitivity (Se). ROC analysis showed that the area under the ROC curve (AUC) values of cELISA [AUC = 0.9941; 95% confidence interval (CI), 0.9898-0.9984] were higher than those of TAT (AUC = 0.7705; 95% Cl, 0.7437-0.7972). A cutoff value of 39.5% was selected with Sp and Se values of 100 (95% Cl, 99.26-100.00) and 97.58 (95% Cl, 96.10-98.50), respectively. The cELISA has excellent futures compared with TAT, such as shortened detection time, no need for pre-treatment of sera, and easy interpretation of the results, and is more suitable for disease surveillance.

Profiling of Humoral Immune Response in Typhoid Patients against Differentially Extracted Whole Cell Bacterial Protein Derived from S. typhi and S. spp

Typhoid fever is a multiorgan infectious disease caused by Salmonella typhi. It is transmitted through fecal oral route and can be fatal without proper treatment. Therefore, early diagnosis of typhoid fever is crucial. In the previous study, we have developed TYPHOIDYNE EIA, which showed excellent synergy between the genus conserved and species-specific antigens in the serodiagnosis of typhoid fever. TYPHOIDYNE EIA can effectively detect and differentiate typhoid patients, typhoid vaccinated subjects, healthy subjects, and subjects with other febrile illnesses. Following the successful development of TYPHOIDYNE EIA, in this report, we further characterize the antigenic components of differentially extracted S. typhi and S. spp recognized by IgM, IgG, and IgA antibody isotypes in typhoid patients and possible typhoid carrier by the western blot (WB) assay. The WB characterization revealed a dynamic pattern of recognition, with significant variations in the number of antigenic bands observed between the differentially extracted arrays of antigens. The reactivity of patient’s sera was divided into 3 regions, with region 1 (≥55 kDa) showing the strongest reactivity followed by region 2 (54 kDa–34 kDa) and region 3 (<34 kDa). Overall, the good synergy expressed in these bands suggests the potential role of these proteins in differentiating typhoid patients with possible typhoid carrier. The antigenic bands highlighted in this study are also identified as prospective biomarkers for diagnostic use and vaccine development.

Development and Application of Real-Time PCR Assay for Detection of Salmonella Abortusequi

Salmonella enterica subsp. enterica serovar Abortusequi is a major pathogen in horse and donkey herds, causing abortion in pregnant equids and resulting in enormous economic losses. A rapid and reliable method is urgently needed to detect S. Abortusequi in herds where the disease is suspected. To achieve this goal, a TaqMan-based real-time PCR assay targeting the gene for the flagellin protein phase 2 antigen FljB was developed. This real-time PCR assay had high specificity, sensitivity, and reproducibility. The detection limit of the assay was 30 copies/μL of standard plasmid and 10 CFU/μL of bacterial DNA. Furthermore, 540 clinical samples, including 162 tissue, 192 plasma, and 186 vaginal swab samples collected between 2018 and 2021 in China, were tested to assess the performance of the developed assay. Compared to the gold standard method of bacterial isolation, the real-time PCR assay exhibited 100% positive agreement for all tissue, plasma and vaginal swab tests. Additionally, this assay detected DNA from S. Abortusequi from 56.7% (34/60) culture-negative tissue and 22.9% (41/179) culture-negative vaginal swab samples from infected equids. Receiver operating characteristic analysis demonstrated that the results of the developed real-time PCR assays were in significant agreement with those of the culture method. The real-time PCR assay can be completed within 45 min of extraction of DNA from samples. Our results show that this assay could serve as a reliable tool for the rapid detection of S. Abortusequi in tissue, plasma, and vaginal swab clinical samples.

Antibiotic resistance of enterobacterial pathogens isolated on the territory of the Northern Kazakhstan

The purpose of this study was to isolate and identify strains of infectious disease pathogens and to determine their antibacterial drug resistance. From 2018-2020, 5322 samples of biological material from animals and birds, products of animal origin were taken at retail outlets, livestock enterprises in Kostanay and North Kazakhstan regions. In the study territories of 20 districts and 4 cities were covered. Phenotypic resistance analysis of the recovered isolates of Salmonella spp. showed a high level of resistance to antibiotics of the tetracyclines (82/137) and nitrofurans (81/137) groups. S. aureus isolates had increased resistance to the β-lactams (124/131) and macrolides (96/131) groups. As a result, the largest number of genes encoding resistance was found to the β-lactams, aminoglycosides, tetracyclines and macrolides groups. The study was carried out within the framework of the project AR05131447 "Monitoring of antibiotic resistance of pathogens of enteropathogenic zooanthroponosis diseases in the Northern Kazakhstan".

Molecular Characterization of Three Tandemly Located Flagellin Genes of Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is a motile, opportunistic pathogen. The flagellum, which is involved in swimming, swarming, adhesion, and biofilm formation, is considered a virulence factor for motile pathogens. Three flagellin genes, fliC1, fliC2, and fliC3, were identified from the sequenced S. maltophilia genome. FliC1, fliC2, and fliC3 formed an operon, and their encoding proteins shared 67–82% identity. Members of the fliC1C2C3 operon were deleted individually or in combination to generate single mutants, double mutants, and a triple mutant. The contributions of the three flagellins to swimming, swarming, flagellum morphology, adhesion, and biofilm formation were assessed. The single mutants generally had a compromise in swimming and no significant defects in swarming, adhesion on biotic surfaces, and biofilm formation on abiotic surfaces. The double mutants displayed obvious defects in swimming and adhesion on abiotic and biotic surfaces. The flagellin-null mutant lost swimming ability and was compromised in adhesion and biofilm formation. All tested mutants demonstrated substantial but different flagellar morphologies, supporting that flagellin composition affects filament morphology. Bacterial swimming motility was significantly compromised under an oxidative stress condition, irrespective of flagellin composition. Collectively, the utilization of these three flagellins for filament assembly equips S. maltophilia with flagella adapted to provide better ability in swimming, adhesion, and biofilm formation for its pathogenesis.

Proximity ligation assay: an ultrasensitive method for protein quantification and its applications in pathogen detection

It is of great significance to establish sensitive and accurate pathogen detection methods, considering the continuous emergence or re-emergence of infectious diseases seriously influences the safety of human and animals. Proximity ligation assay (PLA) is developed for the sensitive protein detection and also can be used for the detection of pathogens. PLA employs aptamer or monoclonal/polyclonal antibody-nucleic acid complexes as proximity probes. When the paired proximity probes bind to the same target protein or protein complex, they will be adjacent to each other and form an amplifiable DNA sequence through ligation. Combining the specificity of enzyme-linked immunosorbent assay (ELISA) and sensitivity of polymerase chain reaction (PCR), PLA transforms the detection of protein into the detection of DNA nucleic acid sequence. Therefore, as an ultrasensitive protein assay, PLA has great potential for quantification, localization of protein, and clinical diagnostics. In this review, we summarize the basic principles of PLA and its applications in pathogen detection. KEY POINTS: • Different forms of proximity ligation assay are introduced. • Applications of proximity ligation assay in pathogen detection are summarized. • Proximity ligation assay is an ultrasensitive method to quantify protein and pathogen.