Latex Agglutination: A Rapid, Specific Immunoassay for Diagnosis of Ruminant Brucellosis

Abstract

Latex agglutination immunoassay is widely applied in diagnosis favored by advances in nanotechnology. This study was designed to investigate an inexpensive approach for producing highly specific protein antigen. Soluble Brucella proteins (SBPs 50) fractions were extracted from reference strain of Brucella abortus (strain 99) by differential precipitation with 50% ammonium sulfate. Analysis of the attained proteins by electrophoresis (SDS-PAGE) resulted in predominant 37.6 kDa protein, a medium-sized 30.6 kDa, and low molecular weight protein of 17.2 kDa when compared with low-molecular-mass marker ranged from (14 kDa to 92 kDa). To sustain as an advanced antigen applied in diagnosis of ruminant brucellosis, covalent coupling of obtained SBPs 50 to carbox-ylated polystyrene microsphere latex beads (0.81 ± 0.15 |im diameter) was used to assess the potential diagnostic utility of latex beads coated with the obtained SBPs. The developed assay (latex agglutination test, LAT) scored high diagnostic specificity (DSp) in all examined species; cattle, buffaloes, sheep, and goats (92.3%, 99.0%, 94.1%, and 95.9%) respectively. The diagnostic sensitivity (DSe) of LAT recorded (97.2%, 95.0%, 91.7%, and 85.6%) for cattle, buffaloes, sheep and goats correspondingly which were relatively lower than other counterpart conventional screening immunoassays; buffered antigens (BAPA and RBT). Kappa agreement values (k) between latex agglutination test (LAT) and complement fixation test (CFT), were (0.90, 0.95, 0.83 and 0.76) for cattle, buffaloes, sheep and goats correspondingly indicating almost perfect correlation in examined species except in goats which showed substantial correlation. Besides DSe, DSp and k agreement, other diagnostic indicators were assessed. From the results of this study, Latex agglutination test coated with SBPs 50 was proved to be an advisable method for diagnosis of ruminant brucellosis due to its high specificity, simplicity, fast, promptness, easy to interpret technique and low cost.