A microbiological multi-plate method to detect cephalosporin residues in milk

Abstract

The aim of this study was to determine the detection capability (CCβ) of a multi-plate diffusion method for selected cephalosporins for which the maximum residue limits (MRLs) in milk have been set (ceftiofur, cefoperazone, cephalexine, cephazoline, cephalonium, cephapirine, cefquinome). The multiplate method was composed of Bacillus subtilis BGA CCM 4062 plates (agar pH of 6, 8 and 7.2); Kocuria rhizophila CCM 552 plate, Geobacillus stearothermophilus CCM 5965 plate and Escherichia coli CCM 7372 plate. Geobacillus stearothermophilus plate showed the highest sensitivity. CCβ for the tested cephalosporins was determined at MRLs or lower, except for cefquinome, which was undetectable even at 12 × the MRL. Kocuria rhizophila plate showed the highest sensitivity to ceftiofur (CCβ = 100 μg/l); cephazoline and cephalonium could not be detected even at 12 × times the MRL. Escherichia coli plate was most sensitive to cefoperazone (CCβ = 60 μg/l). Other than cephapirine, none of the cephalosporins could be detected by B. subtilis BGA (pH 6, 8 and 7.2) plates even at 12 × the MRL. Our results demonstrate the differences in sensitivity to selected cephalosporins of the individual plate methods that together form the multi-plate method. The multi-plate method is sensitive enough to detect most of the tested cephalosporins, with the exception of cefquinome, which could not be detected at levels close to MRL.