Buffer Acidified Plate Brucella Antigen (BAPA).
 The antigen is prepared from a concentrated cell suspension of Co2 independent smooth strain of Br. abortus (Strain 99). The cells are stained with crystal violet and brilliant green stain and suspended in buffered brucella antigen diluent (pH 3.65 + 0.05).
 Glass bottles of 20 ml to apply 600 Diagnostic Unit (DU.) 
 It is used for serological diagnosis of brucellosis in cattle sheep by the plate agglutination test.
 ِA testing box about 48 cm long 33 cm wide and 12 cm deep is employed. However a simple glass plate marked in 4 cm square may be used .
1.        Place 0.08 ml of each serum under test on one squares of the plates.
2.        Shake the antigen bottle until the contents are thoroughly mixed then drop 0.03 ml of the antigen alongside each drop of serum.
3.        Mix the serum and antigen in each drop with a tooth pick or spreader. 
4.        Rotate the plate in the hand for 3 rotations on each occasion 1. after mixing, 2. after 4 minutes and 3. after 8 min then read.
The results are recorded as follows:
·         No agglutination (homogenous) after 8 minutes ……. Negative (-)
·         Weak agglutination (minimal reaction) at the end of 8 minutes ….. suspicious (+)
·         Slight agglutination after 8 minutes …….. (+)
·         Moderate agglutination after 4 minutes ……. (++)
·         Moderate agglutination soon after mixing ……. (+++)
·         Clear agglutination leaving clear solution immediately after mixing …… (++++)
N.B. This is a screen test, any reaction indicates that further test are 
 should be done.
1.        Shake the bottle very well before use. 
2.        Bring both the reactants (the antigen and serum) to room temperature before performing the test.
3.        Readings after 8 minutes, not to be recommended. 
4.        To ensure validity of the antigen use control positive and negative sera. 
 Avoid freezing – keep the antigen at 4 - 8 o C for one year from the date of manufacture.