Antimicrobial residues in milk. Comparison of different agar diffusion methods.

Different agar diffusion methods were compared in order to find a sensitive method for the detection of various antimicrobial residues in milk. A total of 588 producer milk samples were analyzed using subsets of the most sensitive methods. With the IDF method, 2 positive cases (0.34 %) appeared among the producer milk samples, with the Thermocult method 13 positive cases (2.21 and with the Test agar pH 8 method with trimethoprim and glucose 4 positive cases (0.68 %). A combination of the IDF method and the Test agar pH 8 method resulted in 6 positive cases (1.02 and a combination of the Thermocult method and the Test agar pH 8 method in 17 positive cases (2.89 With penicillinase 41 of the positive cases were identified as β-lactam antibiotics and with p-aminobenzoic acid 18 % of the positive cases were identified as sulphonamides. 41 of the positive cases remained unexplained. The best combination for the detection of antimicrobial agents in milk seems to be that of the Thermocult method and the Test agar pH 8 method with trimethoprim and glucose.