Residual antibiotics in milk were identified by high-voltage electrophoresis in 1% agarose gel and bioautographic detection. The test strain Bacillus subtilis BGA was used for the detection, pH of the culture medium was 8.0. An electrophoretic identification map of 13 selected antibiotics has been set up and the following minimal inhibition concentrations (MIC), expressed in microgram per 1 g, have been established: benzylpenicillin 0.06; ampicillin 0.25; streptomycin 0.5; dihydrostreptomycin 0.2; spectinomycin 40; gentamycin 0.06; neomycin 0.15; oxytetracycline 5; tetracycline 2.5; chlortetracycline 1; erythromycin 0.01; tylosin 1; chloramphenicol 20. The established values of MIC were compared with the Maximum Residue Limits (MRL) as defined currently in the legislation of the European Union. The condensation of samples by freeze-drying increased the sensitivity of the method which was used for the identification of residual antibiotics detected by microbiological screening techniques in milk.

Veterinary Research Institute Brno Czech Republic