A COMPARATIVE-STUDY OF A NEWLY DEVELOPED AGAR-DIFFUSION TEST AND BRILLIANT-BLACK REDUCTION TESTS IN CONJUNCTION WITH AN ELISA READER TO MEASURE ANTIBIOTIC RESIDUES IN MILK

The report describes a newly developed agar-diffusion test for the det ection of antibiotic residues in milk, and compares the findings with the brilliant-black reduction tests (BRT BlueStar and BRT AS), The res ults were evaluated with an ELISA-reader. A 55% increase in optical de nsity was chosen to define the sensitivity limit. The agar-diffusion m ethod was tested with the use of decreasing concentrations of antibiot ics. The 3 antibiotics tested represent substances which are used in v eterinary medicine. Consequently, they may be found as residues in bul k tanks. The agar-diffusion test contains spores of B. stearothermophi lus and shows the following detection limits: for Penicillin G 0.0025 IU/ml, for Cefoperazon 0.025 mu g/ml, and for Cloxacillin 0.030 mu g/m l. The BRT BlueStar and the BRT AS (results in parenthesis) tests show detection limits: for Penicillin G 0.0055 IU/ml (0.0075 IU/ml), for C efoperazon 0.05 mu g/ml (0.065 mu g/ml), and for Cloxacillin 0.055 mu g/ml (0.055 mu g/ml). This comparative study demonstrates that the new ly developed agar-diffusion test exhibits more favourable sensitivity limits for the 3 investigated antibiotic residues than the brilliant-b lack reduction tests. The sensitivity limits claimed by the supplier f or BRT BlueStar and BRT AS are basically in line with our findings. th e main advantage is the ''staff independent'' use of the ELISA-reader.