Microbiological system in microtitre plates for detection and classification of antibiotic residues in milk

A novel microbiological system in microtitre plates for the classification of antibiotic residues in milk is presented. The system uses four microbiological bioassays to detect and classify residues of widely used antibiotics on dairy farms. Each bioassay contains a culture medium, acid base or redox indicator, detection capability upgrader or synergist and microorganism spores (Geobacillus stearothermophilus, Bacillus cereus and Bacillus subtilis) that are sensitive to different groups of antibiotics. The system identifies residues of beta-lactams, tetracyclines, sulfamides and quinolones in milk at levels near to their maximum residues limits in 6 h. Thus, this microbial system in microtitre plates presents an alternative to traditional systems in Petri dishes that take 24 h to provide results. The system also has a dichotomous response (positive or negative) that is easy to interpret. Implementation of the system allows a preliminary classification of antibiotics into four groups, prior to subsequent analysis by chromatographic techniques.