Serological diagnosis of bovine brucellosis using B. melitensis strain B115

Novel Vertical Flow Immunoassay with Au@PtNPs for Rapid, Ultrasensitive, and On-Site Diagnosis of Human Brucellosis

Brucellosis is an infectious zoonosis caused by Brucella with clinical symptoms of wavy fever, fatigue, and even invasion of tissues and organs in the whole body, posing a serious threat to public health around the world. Herein, a novel vertical flow immunoassay based on Au@Pt nanoparticles (Au@PtNPs-VFIA) was established for detection of Brucella IgG antibody in clinical serum samples. The testing card of Au@PtNPs-VFIA was manufactured by printing the purified Brucella LPS and goat antimouse IgG on the nitrocellulose membrane as the test-spot or control-spot, respectively. Au@PtNPs labeled with protein G (Au@PtNPs-prG) were concurrently employed as detection probes presenting visible spots and catalysts mimicking catalytic enzymes to catalyze the DAB substrate (H2O2 plus O-phenylenediamine) for deepening color development. The testing procedure of Au@PtNPs-VFIA takes 2-3 min, and the limit of detection (LOD) for Brucella antibody is 0.1 IU/mL, which is faster and more sensitive than that of Au@PtNP-based lateral flow immunoassay (Au@PtNPs-LFIA: 15 min and 1.56 IU/mL, respectively). By comparing with vertical flow immunoassay based on classic Au nanoparticles (AuNPs-VFIA), the Au@PtNPs-VFIA is 32 times or 16 times more sensitive with or without further development of DAB substrate catalysis. Au@PtNPs-VFIA did not react with the serum samples of Gram-negative bacterium infections but only weakly cross-reacted with diagnostic serum of Y. enterocolitica O9 infection. In detection of clinical samples, Au@PtNPs-VFIA was validated for possessing 98.33% sensitivity, 100% specificity, and 99.17% accuracy, which were comparable with or even better than those obtained by the Rose-Bengal plate agglutination test, serological agglutination test, AuNPs-VFIA, and Au@PtNPs-LFIA. Therefore, this newly developed Au@PtNPs-VFIA has potential for rapid, ultrasensitive, and on-site diagnosis of human Brucellosis in clinics.

False Positives in Brucellosis Serology: Wrong Bait and Wrong Pond?

This review summarizes the status of resolving the problem of false positive serologic results (FPSR) in Brucella serology, compiles our knowledge on the molecular background of the problem, and highlights some prospects for its resolution. The molecular basis of the FPSRs is reviewed through analyzing the components of the cell wall of Gram-negative bacteria, especially the surface lipopolysaccharide (LPS) with details related to brucellae. After evaluating the efforts that have been made to solve target specificity problems of serologic tests, the following conclusions can be drawn: (i) resolving the FPSR problem requires a deeper understanding than we currently possess, both of Brucella immunology and of the current serology tests; (ii) the practical solutions will be as expensive as the related research; and (iii) the root cause of FPSRs is the application of the same type of antigen (S-type LPS) in the currently approved tests. Thus, new approaches are necessary to resolve the problems stemming from FPSR. Such approaches suggested by this paper are: (i) the application of antigens from R-type bacteria; or (ii) the further development of specific brucellin-based skin tests; or (iii) the application of microbial cell-free DNA as analyte, whose approach is detailed in this paper.

Rapid vertical flow technique for the highly sensitive detection of Brucella antibodies with Prussian blue nanoparticle labeling and nanozyme-catalyzed signal amplification

Brucellosis is a chronic infectious disease caused by Brucella, which is characterized by inflammation of reproductive organs and fetal membranes, abortion, infertility, and local inflammatory lesions of various tissues. Due to the widespread prevalence and spread of brucellosis, it has not only caused huge losses to animal husbandry, but also brought serious impacts on human health and safety. Therefore, rapid and accurate diagnosis is of great significance for the effective control of brucellosis. Therefore, we have developed a rapid vertical flow technique (RVFT) using Prussian blue nanoparticles (PBNPs) as a marker material for the detection of brucellosis antibodies. Lipopolysaccharide (LPS) was purified and used to detect brucellosis antibodies to improve the sensitivity of this technique. To enhance the sensitivity of serum antibody detection, a single multifunctional compound buffer was created using whole blood as a biological sample while retaining the advantages of typical lateral flow immunoassays. After signal amplification, standard Brucella-positive serum (containing Brucella antibody at 4000 IU mL^-1) could be detected in this system even at a dilution factor of 1 × 10^-2. The detection limit was 40 IU mL^-1, which is ten times that before signal amplification. This RVFT displayed good specificity and no cross-reactivity. This RVFT effectively avoided the false negative phenomenon of lateral flow immunoassays, was easy to operate, had a short reaction time, has good repeatability, and could elicit results that were visible to the naked eye for 2 ~ 3 min without any equipment. Since this method is very important for controlling the prevalence of brucellosis, it holds great promise for application in primary medical units and veterinary brucellosis detection.

Bovine brucellosis - a comprehensive review

Brucellosis is a zoonotic disease of great animal welfare and economic implications worldwide known since ancient times. The emergence of brucellosis in new areas as well as transmission of brucellosis from wild and domestic animals is of great significance in terms of new epidemiological dimensions. Brucellosis poses a major public health threat by the consumption of non-pasteurized milk and milk products produced by unhygienic dairy farms in endemic areas. Regular and meticulous surveillance is essentially required to determine the true picture of brucellosis especially in areas with continuous high prevalence. Additionally, international migration of humans, animals and trade of animal products has created a challenge for disease spread and diagnosis in non-endemic areas. Isolation and identification remain the gold standard test, which requires expertise. The advancement in diagnostic strategies coupled with screening of newly introduced animals is warranted to control the disease. Of note, the diagnostic value of miRNAs for appropriate detection of B. abortus infection has been shown. The most widely used vaccine strains to protect against Brucella infection and related abortions in cattle are strain 19 and RB51. Moreover, it is very important to note that no vaccine, which is highly protective, safe and effective is available either for bovines or human beings. Research results encourage the use of bacteriophage lysates in treatment of bovine brucellosis. One Health approach can aid in control of this disease, both in animals and man.

A quantum dot fluorescent microsphere based immunochromatographic strip for detection of brucellosis

BACKGROUND

Brucellosis is a serious zoonosis disease that frequently causes significant economic loss in animal husbandry and threatens human health. Therefore, we established a rapid, accurate, simple and sensitive fluorescent immunochromatographic strip test (ICST) based on quantum dots (QDs) for detection the antibodies of Brucella infection animals serum.

RESULTS

The test strips were successfully prepared by quantum dot fluorescent microspheres (QDFM) as tracers, which were covalently coupled to an outer membrane protein of Brucella OMP22. The outer membrane protein OMP28 and monoclonal antibodies of OMP22 were separately dispensed onto a nitrocellulose membrane as test and quality control lines, respectively. The critical threshold for determining negative or positive through the ratio of the fluorescent signal of the test line and the control line (H_T / H_C) is 0.0492. The repeatability was excellent with an overall average CV of 8.78%. Under optimum conditions, the limit of detection was 1.05 ng/mL (1:512 dilution). With regard to the detection of brucellosis in 150 clinical samples, the total coincidence rate of ICST and Rose Bengal plate test (RBPT) was 97.3%, the coincidence rate of positive samples was 98.8%, the coincidence rate of negative samples was 95.3%, the sensitivity of RBPT is 1:32, and no cross reaction with the sera of other related diseases was observed.

CONCLUSION

In our present study, the QDFM has promising application for on-site screening of brucellosis owing to its high detection speed, high sensitivity, high specificity and low cost.

Development of an Immunodiagnostic Test for Screening Human Brucellosis Cases Using the Whole-Cell Antigens of Brucella abortus

Background

Human brucellosis is an important zoonotic disease of public health and often remains neglected owing to lack of sensitive and efficient diagnostic methods. This study evaluates diagnostic utility of in-house designed enzyme-linked immunosorbent assay (ELISA) using whole-cell antigens of Brucella abortus (B. abortus) S19 against the commercially available kits.

Methods

A prospective cohort study involving different populations within the Vidarbha regions of Maharashtra, India was conducted through camps organised from May 2009 to October 2015. A total of 568 serum samples were collected from high-risk people recruited as study cohorts based on inclusion criteria, additional risk factors and clinical symptoms. Samples were evaluated by indirect ELISA using the whole-cell antigens of B. abortus. The results were compared with the commercially available IgG detection ELISA kit to ascertain the specificity and sensitivity of the developed test.

Results

Fever, body ache, joint pain, lower back pain, loss of appetite and weight loss were major symptoms associated with the disease. With the cut-off of > 0.8, the positivity of brucellosis infection was at 12.32% (70/568) compared to 9.33% (53/568) as detected by the commercial kit. The in-house developed ELISA method yielded a sensitivity of 87.5% and specificity of 99.18% as compared to the commercial kits (sensitivity −80.30% and specificity −99.6%).

Discussion

The B. abortus S19-derived whole-cell protein-based ELISA is rapid and cost-effective and can be used for screening brucellosis infection in lieu of the commercially available ELISA kits.

Brucella melitensis B115-based ELISA to unravel false positive serologic reactions in bovine brucellosis: a field study

Background

Brucellosis is a zoonosis whose incidence is not declining worldwide despite the global effort to control the disease. Accurate and precise diagnosis is a crucial step in any prophylaxis program but single tests to unequivocally detect animals infected with Brucella spp. are currently unavailable. In Italy, serological diagnosis of bovine brucellosis is performed with two official tests: a rapid agglutination test (i.e., Rose Bengal Plate test, RBPT) and a complement fixation test (CFT) that detect antibodies directed mainly to the smooth lipopolysaccharide (S-LPS). Neither of the two tests is able to avoid the detection of false positive serological reactions (FPSRs) caused by bacteria sharing S-LPS components with Brucella spp. and responsible for the single reactors (SR) phenomenon. A B. melitensis R strain-based ELISA showed a good diagnostic performance in unravelling FP animals; however, since a limited number of animals were analyzed in that study, a large field study was conducted here to discriminate between Brucella-infected from FP animals, with the final aim of reducing the unnecessary slaughter of the latter. An ELISA based on a R strain of Brucella, i.e., Brucella melitensis B115, was employed to measure specific IgG responses in a collection of bovine sera (n = 648). Sera were obtained from 180 farms (either officially brucellosis-free or not brucellosis-free) recruited during an extended period of time (2014–2018) and were preliminarily assayed with the official tests by the Italian Reference Centers and then subjected to the ELISA.

Results

Negative sera, when subjected to the ELISA, gave O.D. values below the cutoff; SR sera, i.e. RBPT positive and CFT negative, as well as double positive (DP) sera, i.e. RBPT and CFT positive, gave O.D. values that were below the cutoff. All positive sera, i.e. from Brucella-infected animals, were RBPT positive and CFT positive (ICFTU ranging from 20 to 1280) and gave ELISA O.D. values above the cutoff.

Conclusions

The B. melitensis B115-based ELISA systematically unravelled all false positive (FP) sera while confirming the diagnosis in Brucella-infected animals. Thus, the test employed in the present study may complement the official assays to avoid the costly slaughter of FP animals.

Research Progress on Brucellosis

Brucellosis is a debilitating febrile illness caused by an intracellular Brucella. The disease is distributed in humans and animals widely, especially in developing countries. Ten species are included in the genus Brucella nowadays; four species of them are pathogenic to humans, which make brucellosis a zoonosis with more than 500,000 new cases reported annually. For human brucellosis, the most pathogenic species is B. melitensis followed by B. suis, while B. abortus is the mildest type of brucellosis. The infection mechanism of Brucella is complicated and mostly relies on its virulence factors. The therapy of the disease contains vaccination and antibiotic. However, there are some defects in currently available vaccines such as the lower protective level and safety. Thus, safe and efficient vaccines for brucellosis are still awaited. The dual therapy of antibacterial is effective in the treatment of brucellosis if a rapid and exact detection method is found.

Recombinant Omp2b antigen-based ELISA is an efficient tool for specific serodiagnosis of animal brucellosis

Control of brucellosis as a worldwide zoonotic disease is based on vaccination of animals and diagnosis of infected cases to be eradicated. Accurate and rapid detection of infected animals is of critical importance for preventing the spread of disease. Current detection of brucellosis is based on whole-cell antigens and investigating serum antibodies against Brucella lipopolysaccharide (LPS). The critical disadvantage is misdiagnosis of vaccinated animals as infected ones and also cross-reactions with other Gram-negative bacteria. Recombinant outer membrane protein 2b (Omp2b) of Brucella abortus was evaluated as a novel serodiagnostic target in comparison to conventional tests which are based on LPS. Recombinant Omp2b (rOmp2b) was expressed in Escherichia coli BL21 and purified by Ni²⁺-based chromatography. rOmp2b was evaluated in an indirect enzyme-linked immunosorbent assay (ELISA) system for diagnosis of brucellosis, with sera from Brucella-infected mice along with negative sera and sera from mice which were inoculated with other Gram-negative species for assurance of specificity. Thereafter, cattle sera collected from different regions were assessed along with known negative and known positive serum samples. We found that Omp2b can discriminate between Brucella-infected animals and non-infected ones. Results for assessment of two hundred and fifty cattle sera by Omp2b-based indirect ELISA which were compared to Rose Bengal plate agglutination test (RBPT) and serum tube agglutination test (SAT) showed that our proposed procedure has the sensitivity of 88.5%, specificity of 100%, and accuracy of 90.8%. We suggest that recombinant Omp2b could be used as a protein antigen for diagnosis of brucellosis in domestic animals and can be evaluated for detection of human brucellosis.