An Arkray Brucella Melitensis Antigen is a diagnostic reagent used to detect antibodies against the Brucella melitensis bacteria in human serum, which helps diagnose brucellosis, a zoonotic disease transmitted through infected animal products. The reagent consists of smooth, stained, attenuated suspensions of Brucella bacteria that cause an agglutination (clumping) reaction in the presence of specific antibodies in the patient's serum. No agglutination indicates the absence of these antibodies.