Basis for the evaluation of the microbiological risks due to veterinary drug residues in food

The history of the establishment of safe residue levels is reviewed. Current internation agreements within the FAO/WHO Codex Alimentarius programme and EC legislation establish these levels on the basis of toxicology studies. In addition to conventional toxicological effects, other effects such as the effects of drugs on the immune system, and pharmacological effects should be taken into account. The latter also include specific effects of residues of veterinary antibiotics on the human gut flora. The methods for the assessment of these effects are evaluated. Studies in human volunteers enable the establishment of a no-effect level in conditions which are the most closely mimicking the conditions of use. However, they are less favourable from a practical and ethical point of view. Studies with animal models can be used; for example human intestinal flora can be inoculated to gnotobiotic mice. These models need nevertheless to be further validated. Studies in vitro, such as those to determine the MIC, are relatively simple to carry out and inexpensive, but are not always representative of the relevant bacteria, and may not take into account factors such as, Ph, anaerobiosis and the barrier effect.