A microbiological assay system for assessment of raw milk exceeding EU maximum residue levels

A microbiological multiplate system is described, which can be used to eval uate the milk residue state near the established EU MRLs for beta-lactam an tibiotics, tetracyclines, macrolides, aminoglycosides, quinolones, polymyxi ns, and other antibiotics like rifamycin and novobiocin. The multiplate sys tem consists of a Bacillus stearothermophilus var, calidolactis plate at pH 8.0, a Bacillus cereus plate at pH 6.0, a Micrococcus luteus plate at pH 8 .0, Bacillus subtilis plates at pH 7.0 (sulpha plate) and pH 8.0, an Escher ichia coli plate at pH 6.0 and a Staphylococcus epidermidis plate at pH 6.0 . Among the 48 antimicrobial drugs tested the multiplate system did not rea ch the required sensitivities for sulphanilamide, cefquinone, spectinomycin and colistin with respect to established MRLs for milk. The mean variation coefficient of reproducibility for the 7 test plates ranged between 4.5 (M . luteus plate) and 9.8% (E. coli plate) at MRL level. Based on the inhibit ion zone patterns an indication can be given of the type of drug residue in volved. For each test plate a so-called action level is proposed below whic h the raw milk fulfils the EU MRL criteria, except for cefquinome, spectino mycin, tylosin, colistin, trimethoprim and sulphanilamide. (C) 1999 Elsevie r Science Ltd. All rights reserved.