During infection, group A streptococci produce a range of enzymes (including streptodornase B and streptolysin O) that contribute to their pathogenicity.
These different molecules, in particular streptodornase B, are immunogenic. Streptodornase or DNAse causes the degradation of nucleic acids. The human body responds to infection via the formation of specific antibodies targeted against these toxins. The DOR-BAR kit enables the semi-quantitative detection of anti-streptodornase B antibodies (ASDOR) from human serum, thus confirming an active or recent streptococcal A infection.
Each DOR-BAR tray includes:
A negative control well (containing streptodornase B, but no serum) to verify the depolymerization of the substrate by streptodornase,
A positive control (containing serum but no streptodornase B) to check that depolymerization does not occur in the presence of serum and the substrate.
The serodiagnosis of group A streptococcus can be taken a step further with the ASO-BAR kit which allows the titration of anti-streptolysine O antibodies (ASLO) (Ref. 04125).
The detection of anti-streptodornase B antibodies is based upon the neutralization of the streptodornase B depolymerization activity by antibodies present in the test serum. The tray contains increasing concentration of dehydrated streptodornase for determination of the antibody concentration. The immunological complexes that are formed are revealed by the addition of a color indicator. The inhibition of streptodornase B activity by anti-streptodornase B antibodies leads to a reduction in depolymerization of the substrate (DNA) which is visually read (color change from blue to pink).
The DOR-BAR is a practical test, with no need for serial dilution, a lyophilized substrate (single use vial) and individual tray packaging. Each DOR-BAR tray is a divisible tray of 2 x 10 wells (2 tests per tray).
The reaction is carried out in wells 1 to 8 of the tray. These wells contain increasing concentrations of streptodornase B in order to enable the determination of the serum antibody concentration.
The antibody titre corresponds to the last well of the tray that remains blue.
Easy-to-read and easy-to-interpret results
Absence of a color change (medium blue or blue-violet) The absence of a color change of the medium in the wells correlates to there being sufficient anti-streptodornase B antibodies in the test serum in order to neutralize the streptodornase B in the wells of the tray. Presence of a color change (medium pink or pink-violet) The presence of a color change of the medium in the wells to pink or pink-violet correlates to there being an insufficient concentration of anti-streptodornase B antibodies in the test serum to neutralize the streptodornase B in the wells of the tray.
The titre of anti-streptodornase B antibodies in the serum, in U/ml, corresponds to the LAST WELL THAT DOES NOT DEMONSTRATE A COLOR CHANGE (last well that remains blue or blue-violet). A titre greater than 200 U/mL in adults and 300 U/mL in children is considered to be pathological.
Vial of diluant containing imidazole
Vial of lyophilized medium containing the substrate (DNA), a color indicator and bovine albumin
Divisible tray of 2 x 10 wells (2 tests), individually wrapped in aluminum sachets
Vial of positive control titered at 600 U/mL (human serum)
Stability and Storage
The reagents stored at 2-8 °C are stable until the expiry date.
The DIL reagent is stable at 2-8 °C until the expiry date.
The reconstituted SUBS is stable at 2-8 °C until the expiry date.
The unused half of the DOR-BAR tray is stable for 2 months at 2-8 °C, provided that it is stored hermetically in its original packaging.
A comparative study was carried out between the DOR-BAR and the streptodornase B (Fumouze).
The percentage of agreement was 100% for the negative serums.
The percentage of agreement was 90% for the positive serums.
Material required but not provided
Automatic pipette(s) appropriate to the volumes measured