Lennart Wahlström looks at a reliable method for the screening of veterinary drug residues.
Animals used for food production are often treated with a variety of antibiotics and hormones for therapeutic purposes and growth promotion, which can be subsequently consumed by humans. Consumption of contaminated foodstuffs may result in acute food poisoning, allergic reactions or the development of antibiotic resistant micro-organisms.
To protect consumers, regulatory authorities closely control the level of drug residues entering the human food chain, consequently live animals and resultant foodstuffs need to be rapidly tested using detection methods with high degrees of sensitivity to ensure contamination levels do not exceed specified legal limits.
Now, Biacore offers a reliable method for the detection of veterinary drug residues, with kits specifically available for use with SPR technology to rapidly measure levels of contaminants, such as sulphonamides, streptomycin, chloramphenicol and ß-agonists (ractopamine, clenbuterol salbutamol, and about 10 more).
Analysis of a sample can be completed in minutes with a high degree of sensitivity and precision. Here, some of the important veterinary residues and the available products will be presented.
Sulphonamides are a family of broad-spectrum synthetic bacteriostatic antibiotics, which can be used against most gram-positive and many gram-negative organisms as well as protozoa.
Sulphonamides have both therapeutic and prophylactic applications in veterinary medicine. The EU has established a Maximum Residue Limit (MRL) of 100ppb for all parent drugs (or combination of sulphonamides) in edible tissue. The US has applied similar residue limits. The resistance of animal pathogens to sulphonamides is widespread as a result of more than 50 years of therapeutic use. Repeated low dosage is the ideal environment within which resistance factors can develop and spread. This has reduced the effectiveness of sulphonamide use in veterinary medicine and could have serious implications for human medicine.
Using Qflex Kit Sulphonamides with Biacore Q provides a rapid, reliable and automated detection of sulphonamides in food. In contrast to traditional immunoassay techniques, the Biacore assay provides broad-spectrum detection of multiple types of sulphonamide residues and shows no cross-reactivity with the inactive acetylated metabolite. This assay therefore makes an important contribution towards the improved monitoring of antibiotic residues in food
Chloramphenicol is a broad spectrum antibiotic with excellent antibacterial and pharmacokinetic properties. However, in human medicine its use is often associated with the adverse development of aplastic anemia, a rare but serious blood disorder, resulting in the aunexplained' failure of bone marrow to produce blood cells. For this reason it has been banned from use in food producing animals including honey bees in the European Union, the United States of America, Canada and many other countries. Conventional methods for the detection of chloramphenicol include microbiological assays, immunoassays, chromatographic methods and mass spectroscopy. Very low detection limits are vital to monitor the illegal use of this drug and some of the methods lack the necessary sensitivity while others require long pre-treatment of samples.
The combination of the Biacore Q system and the Qflex Kit Chloramphenicol facilitates routine end use for the detection of Chloramphenicol residues in meat, shellfish, milk and honey. Providing an unrivalled alternative to traditional methods, the assay is a robust, automated, label-free inhibition method reducing the risk of experimental errors. Sample preparation is minimal. Limit of detection in milk is 0.025ppb, in honey 0.07ppb, in chicken 0.02 and in shellfish 0.073ppb.
Growth promoters in livestock
ß-agonist drugs (eg clenbuterol, salbutamol) are very effective growth promoters when fed to farm animals at high doses. Although the economic benefits of this practice can be substantial, it can give rise to the presence of toxic residues in meat. Several cases of acute food poisoning resulting from the ingestion of contaminated meat containing the ß-agonist Clenbuterol have been reported throughout Europe. As a result this drug group is banned from use in livestock production.
The Qflex kit Clenbuterol and the recommended sample preparation procedure allows the extraction and detection of at least 13ß-agonists from liver samples at concentrations ranging from below 0.1ngg-1 to almost 1.5ngg-1.
The ß-adrenergic-agonist ractopamine can enhance the growth rate of treated animals by promoting the repartitioing of fat into muscle. The use of ractopamine within the European Union is banned under Council Directive 96/22/EC1. In the USA it is marketed under the trade name Paylean (Elanco Animal Health) as a feed additive, and has received approval from the US Food and Drug Administration's (FDA) Center for Veterinary Medicine (CVM) for use in pig production.
The validated protocols for the determination of ractopamine residues that have been developed for use with BiacoreQ, provide rapid, reliable, sensitive and automated procedures for the analysis of porcine urine and liver. The limit of detection in urine (without deconjugation) is 0.11ng/ml and in liver 0.17ng/ml.
The aminoglycoside antibiotics streptomycin and dihydrostreptomycin are licensed for use in modern agricultural practice for the treatment of bacterial infections in cattle, sheep, pigs and poultry. In combination with penicillins they are the most widely used antibiotics for the treatment of mastitis. Streptomycin is also used for the treatment of bacterial honeybee diseases, such as European Foulbrood, and is also intensively used for the control of firelight, which affects fruit trees mainly during blossom. Consequently tree-spraying with high concentrations of streptomycin creates a contamination chain: pollen-nectar-bee-honey.
The streptomycin kit has been validated for bovine milk, porcine muscle, porcine kidney as well as honey and provides a high degree of sensitivity and reliability. The kit can be used directly on milk with fat content of up to 3.5percent. Honey samples require mixing with buffer follow by pH adjustment to neutral. Limit of detection in milk is 28µg/l, in honey 15µg/l, in kidney 50µg/kg and in muscle 69µg/kg.
As consumer pressure increases, both regulatory bodies and food producers need rapid, robust and accurate methods for detecting drug residues in food. SPR technology offers a means of achieving this, with results that are comparable to LC-MS in terms of accuracy, but that additionally offer the time savings that the industry needs.
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Lennart Wahlström is with Biacore AB, Uppsala, Sweden. www.biacore.com