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.

Diagnostic potential of Brucella melitensis Rev1 native Omp28 precursor in human brucellosis

Serologic tests for brucellosis aim to detect antibodies produced against membranous lipopolysaccharide of bacteria. Diagnostic use of this method is limited due to false positiveness. This study evaluates an alternative antigen to lipopolysaccharides (LPS), outer membrane 28-precursor-protein, of Brucella melitensis Rev1 for its diagnostic value. Omp28 precursor of B. melitensis Rev1 was cloned, expressed, and purified. 6-His and sumo epitope tags were used to tag the protein at N-termini. Omp28 gene was amplified based on the ORF sequence and cloned into a pETSUMO vector. The recombinant construct was propagated in Escherichia coli One Shot^® Mach1™ cells then transformed into E. coli BL21(D3) cells for protein expression. The purified protein was studied in an indirect ELISA for diagnosis of brucellosis. Sera samples from 60 patients were screened by ELISA and the results were compared to Rose Bengal plate test. Recombinant antigen-based iELISA has given a successful outcome with the sensitivity, specificity, positive predictive value, and negative predictive value of 87.8%, 96.2%, 96.6%, and 78.78%, respectively. In conclusion, recombinant production and purification of the immunodominant Omp28 precursor protein has been achieved successfully in a one-step process with efficient yield and can be used for diagnosis of brucellosis in humans.

Expression and regulation of the ery operon of Brucella melitensis in human trophoblast cells

Brucellosis is primarily a disease of domestic animals in which the bacteria localizes to fetal tissues such as embryonic trophoblast cells and fluids containing erythritol, which stimulates Brucella spp. growth. The utilization of erythritol is a characteristic of the genus Brucella. The ery operon contains four genes (eryA, eryB, eryC and eryD) for the utilization of erythritol, and plays a major role in the survival and multiplication of Brucella spp. The objective of the present study was to conduct a preliminary characterization of differential genes expression of the ery operon at several time points after Brucella infected embryonic trophoblast cells (HPT-8 cells). The result showed that the ery operon expression was higher in HPT-8 cells compared with the medium. The relative expression of eryA, eryB and eryC peaked at 2 h post-infection in HPT-8 cells, and eryD expression peaked at 3 h post-infection. The expression of eryA, eryB and eryC may be inhibited by increased eryD expression. However, the expression of the ery operon was stable in the presence of erythritol in cells. 2308Δery and 027Δery mutants of the ery operon were successfully constructed by homologous recombination, which were attenuated in RAW 264.7 murine macrophages. The characterization of the ery operon genes and their expression profiles in response to Brucella infection further contributes to our understanding of the molecular mechanisms of infection and the pathogenesis of brucellosis.