Microbiological 5-plate Screening Method for Detection of Tetracyclines, Aminoglycosides, Cephalosporins and Macrolides in Milk

Within the field of food hygiene and food control, the antibiotic residues in food of animal origin are analysed because their presence may have undesirable consequences. These include for example, allergic reactions in people, spread of resistance to antibiotics among microorganisms and damages in the food industry. Methods available for the detection of antibiotic residues in food are microbial, chemical and immunoassays. Microbial methods are used as screening methods and are always the first choice for this purpose. The aim of our study was to develop a microbial method for the detection of antibiotic residues from the macrolide, aminoglicoside, cephalosporine and tetracycline families. The study involved investigation of bacterial test strains and establishment of the limits of detection (LOD) of antibiotics. For cephalosporines and macrolides, the most appropriate sensitive strain proved to be Micrococcus luteus ATCC 9341, for aminoglicosides Bacillus subtilis BGA and for tetracyclines Bacillus cereus ATCC 11778. A significant component in our experiment were the so-called confirmation solutions. Magnesium sulphate inactivates aminoglicosides and can be used to confirm their presence when more than one antibiotic group can produce inhibition zones on the same plate. Cephalosporinase inactivates cephalosporines and was used to distinguish this group of antibiotics from macrolides. The LOD was at or below the allowed maximum residue level (MRL) for all tested antibiotic groups.