Establishment of a microbiologically acceptable daily intake of antimicrobial drug residues

Abstract

A model is presented to calculate the microbiologically acceptable daily intake (ADI(m)) of antibiotic residues in food products. The ADI(m) calculation is based on MIC values for indicator bacteria Escherichia coli, Bacteroides fragilis, Bifidobacterium spp. and Eubacterium spp., established under gut-like conditions in an in vitro simulation model. The maximum residue level (MRL) for residues in food products can be derived from the ADI(m). Four phases can be distinguished in this gastro-intestinal simulation model, namely: 1. In vitro determination of the MIC for each bacterial strain by a standard method. 2. Incorporation of the drug into food (meat, milk) followed by testing of the stability of the antibiotic under gut-like conditions. 3. Adjustment of the 'gastric' fluid to the duodenal situation, inoculation with the test bacteria and anaerobic incubation at 37°C for at least 18 h. 4. MIC reading confirmed by counting bacteria growing on specific solidified media. In this study the method for calculation of ADI(m) and MRL is given for flumequine as model drug. On the basis of MIC50 values for E. coli strains, a MRL for flumequine of 1.0 μg/g meat or 0.25 μg/ml milk was calculated. It is suggested that, depending on the antibacterial spectrum of the antibiotic involved, the ADI(m) can be determined with selected indicator bacteria, incubated under simulated gastrointestinal conditions.