Establishment of a microbiologically acceptable daily intake of antimicrobial drug residues

Relationship between drug structure and minimal inhibitory concentration value used for acceptable daily intake analysis

The minimal inhibitory concentration (MIC) of an antimicrobial agent for a microbial population (MIC(50, obs) and MIC(90, obs)) is an interpolated value determined for antibacterial drugs by in vitro methods. Many studies have tried to determine the correlation between the MIC(50, obs) or MIC(90, obs) value and the physicochemical parameters to allow quantitaive structure activity relationship (QSAR) predictions of efficacy. A rigorous evaluation of approaches to this problem is presented here. In order to find a correlation between chemical structure and the derivatives of the MIC values for 9 indicatory bacterial strains, it is necessary to employ a number of physicochemical parameters in combination. Only an arithmetic expression composed of many features illustrating the chemical structure of the molecule can be linked to the ƒMIC(50, obs) value. This article demonstrated that, despite the complexity of the MIC value used as the end point, it is possible to validate the model in a limited extent.

Approaches in the safety evaluations of veterinary antimicrobial agents in food to determine the effects on the human intestinal microflora

The administration of antimicrobial agents to livestock creates potential for antibiotic residues to enter the food supply and be consumed by humans. Therefore, as a process of food animal drug registration, national regulatory agencies and international committees evaluate data regarding the chemical, microbiologic, pharmacokinetic, pharmacodynamic, pharmacologic, toxicologic, and antimicrobial properties of veterinary drugs to assess the safety of ingested antimicrobial residues to consumers. Currently, European, Australian and United States guidelines for veterinary drug registration require a safety assessment of microbiologic hazards from consumption of antimicrobial residues taking into account the potentially adverse effects on human intestinal microflora. The main concerns addressed are selection of resistant bacteria in the gastrointestinal tract and disruption of the colonization barrier of the resident intestinal microflora. Current requirements differ among national agencies. Efforts are ongoing internationally to review and harmonize approaches and test methods and protocols for application to these microbiologic safety evaluations of antimicrobial drug residues in food. This review describes the background to current regulatory approaches used in applying in vitro and in vivo methods to set a microbiologic acceptable daily intake for residues in food derived from animals treated with an antimicrobial agent. This paper also examines the current research needs to support these evaluations.

Human health hazards associated with the administration of antimicrobials to slaughter animals. Part I. An assessment of the risks of residues of tetracyclines in pork

This article describes the assessment of consumer risks of residues of tetracyclines in slaughter pigs in the Netherlands. The assessed risks were toxic and allergic reactions, and the disturbance of the consumers' intestinal flora. Toxic and allergic reactions in humans and animals have only been observed at therapeutic doses, affecting between an estimated 1 in 5,000 and one 1 in 140,000 individuals exposed. Residues of tetracyclines in pigs are closely associated with treatment with injectable formulations. Established Maximum Residue Levels (MRLs) do not reflect actual consumer risks in case a limit is violated incidentally. For example, when the established MRLs for tetracyclines in meat are exceeded with a factor 400, 40,000, and 200,000, respectively, the actual risk of an adverse drug reaction for the consumer following a single consumption of this meat is maximally 1 in 3 million, 1 in 300,000, and 1 in 8,000, respectively. At the current estimated low levels of incidental exposure via pork, the annual risk of negative health effects for a random consumer is estimated at maximally 1 in 33 million. The annual risk that a temporary disturbance of the intestinal flora may also result in a facilitated infection with certain enteropathogens, such as Salmonella spp., is estimated at 1 in 45 million. It is concluded that the current microbiological risks of pork are greater than the risks of residues of tetracyclines as such, and that the control of the microbiological risks of pork should therefore be given first priority.

Reduction of Campylobacter jejuni in a simulated chicken digestive tract by Lactobacilli cultures

Studies were conducted to investigate the impact of a selected lactobacilli mixed culture on Campylobacter jejuni in simulated chicken digestive tract models. Veronal buffer solutions corresponding to the pH of successive segments of the chicken digestive tract were prepared. The lactobacilli mixtures were prepared by mixing four fresh lactobacilli cultures, including Lactobacillus acidophilus, Lactobacillus fermenentum, Lactobacillus crispatus, and Lactobacillus brevis. The C. jejuni and lactobacilli mixture were mixed with sterile poultry feed, and the previously prepared veronal buffer solutions were then added separately. The mixture was incubated at 41.1 degrees C for various lengths of time with periodic agitation. The feed passage time for five segments of the digestive tract were adopted: crop (pH 4.5), 30 min; proventriculus (pH 4.4), 15 min; gizzard (pH 2.6), 90 min; small intestine (pH 6.2), 90 min; and large intestine (pH 6.3), 15 min. The Campylobacter and lactobacilli were enumerated. An antagonistic effect on C. jejuni by the tested lactobacilli spp. was found in individual sections and the complete simulated digestive tract models. In the simulated complete chicken digestion system, no C. jejuni were found during the final incubation period when a lactobacilli mixture was present. The results of this in vitro study indicate the potential value of future in vivo studies.

Evaluation of veterinary drug residues in food for their potential to affect human intestinal microflora

The use of veterinary drugs in food-producing animals may result in trace quantities of the drugs or their metabolites being present as residues in food. The effects of veterinary drugs intended for use in food-producing animals on intestinal microflora are evaluated in drug registration since these residues may pose a risk due to their antibiotic activity. This article reviews the different in vivo and in vitro experimental test systems and approaches used by animal health industries, contract laboratories, and regulatory authorities to assess the safety of veterinary drug residues in foods for human consumption. Furthermore, we propose a systematic approach to assess the effects and safety of veterinary drug residues on the human intestinal microflora.

The use of microbiological end-points in the safety evaluation and elaboration of maximum residue limits for veterinary drugs intended for use in food producing animals

The safety evaluation of veterinary drugs intended for use in food producing animals relies heavily on the results of toxicity studies in laboratory animals, supported where possible by any data resulting from human exposure. The general approach involves the calculation of an acceptable daily intake which in turn can be used to elaborate maximum residue limits. It is an approach used in the European Union, in other countries and at the international level. In recent years, concern has been expressed over the presence of microbiologically active residues of veterinary drugs in food and their possible effects on the human gastrointestinal microflora. Methodologies for conducting microbiological safety studies have been investigated and approaches to microbiological safety assessments have been debated. The whole approach has proved to be controversial, partly because there are considerable doubts over the ability of low concentrations of antibiotic substances to produce adverse effects on the human gut flora and partly because there are no validated methods for testing for these attributes. This paper reviews the problems in some detail and discusses the regulatory consequences.