The quinolones (or chinolones) are a family of synthetic broad-spectrum antibiotic drugs. They inhibit the gyrase enzyme and are therefore also known as gyrase inhibitors.

Gyrase inhibitors are divided into four subgroups. The majority of quinolones belong to the subgroup of fluoroquinolones, which have a fluoro-group attached at the central ring system, typically at the 6th position. The fluoroquinolones belong to the so called second generation quinolones. Some of these are admitted as antibiotics in veterinary medicine for food producing animals. Fluoroquinolones are broad spectrum antibiotics against a lot of bacterial species. They are used frequently in veterinary medicine especially for cattle, pigs and chicken. The usage of fluoroquinolones has increased in the past years because large amounts of these antibiotics were applied to prevent infectious diseases, especially in chicken, swine and fish/shrimp farming. The wide use in food producing animals has generated microbial resistances. This led to an amendment of Council Regulation (EEC) No 2377/90 and in the introduction of MRLs (Maximum Residue Limits) for some fluoroquinolones.

Chloramphenicol is a broad spectrum antibiotic which is frequently employed in animal production for its excellent antibacterial and pharmacokinetic properties. However, in humans it leads to hematotoxic side effects, in particular chloramphenicol-induced aplastic anaemia for which a dosage-effect relationship has not yet been established. This has led to a prohibition of chloramphenicol for the treatment of animals used for food production.

Chloramphenicol (2,2-dichloro-N-[(1R,2R)-1,3-dihydroxy-1-(4-nitrophenyl)propan-2-yl]acetamide), produced by Streptomyces venezuelae, was first discovered in 1947 and has been used in veterinary medicine since the 1950s. Today, the use of the broad spectrum antibiotic Chloramphenicol (CAP) is illegal for the administration in food-producing animals in the EU and many other countries worldwide. It is still frequently employed in animal production because of its excellent antibacterial and pharmacokinetic properties and low price. The mechanism of action of Chloramphenicol is bacteriostatic, inhibiting the protein synthesis in bacterial ribosomes. In humans, residues of CAP can cause myelosuppression (damaging the bone-marrow), and the potentially lethal chloramphenicol-induced aplastic anemia. No safe residue level could be established for these side effects. In order to ensure consumer health this led to a complete ban of chloramphenicol for the treatment of animals used for food production and a zero-tolerance for chloramphenicol residues. The EU established a Minimum Required Performance Limit (MRPL) for all test systems of 0.3 ppb.

The chemical structure of chloramphenicol has 8 different stereoisomers, of which only one (RR-p-CAP) is biologically active. The test kit it specific to this stereoisomer. The RIDASCREEN® Chloramphenicol quantitative ELISA is validated for a wide variety of matrices (milk, milk powder and milk products, honey, meat, fish, shrimp, eggs, feed, plasma and serum). In addition, the new version R1511 can also detect the metabolite chloramphenicol glucuronide, allowing for the direct screening of urine.

Nitrofurans are synthetic broad-spectrum antibiotics, which are frequently used in animal production due to their excellent antibacterial and pharmacokinetic properties. They have also been used as growth promoters during the production of shrimp, poultry and pigs.

Long term animal experiments have shown that the parent compounds and their metabolites have carcinogenic and mutagenic characteristics. This led to the prohibition of nitrofurans for the treatment of animals used for food production. In 1993, the EU banned the nitrofurans furaltadone, nitrofurantoin and nitrofurazone for use in animals used as sources of food, and in 1995 the use of furazolidone was also prohibited. The analysis of nitrofurans is based on the detection of the tissue bound metabolites of nitrofurans. The parent compounds are difficult to detect accurately since they are metabolized very rapidly after treatment. The tissue bound nitrofuran metabolites however are present for a long time after administration and they are used to detect nitrofuran abuse.

There are different types of nitrofurans:

• Nitrofurantoin: 1-Aminohydantoin (AHD)
• Furaltadone: 3-Amino-5-morpholinomethyl-2-oxazolidinone (AMOZ)
• Furazolidone: 3-Amino-2-oxazolidinone (AOZ)
• Nitrofurazone: Semicarbazide (SEM)

Prior to analysis, the metabolites have to be derivatized by incubation with 2-Nitrobenzaldehyde into NP-AHD, NP-AMOZ, NP-AOZ and NP-SEM.

β-Lactam antibiotics were named after their characteristic five-membered β Lactam ring and form a large group of antibiotics. They are classified by their chemical structure in several subgroups, whereas the most important ones are the penicillins, cephalosporins and carbapenems.

The penicillins were discovered accidentally in 1928 by Alexander Fleming and inhibit cell wall synthesis of gram positive bacteria. Despite their early discovery, they are still the most widely used group of antibiotics in the world. Especially for mastitis, a bacterial infection of the dairy cow udder, they are the first line treatment. For reasons of consumer protection and process safety in the dairy industry, in Commission Regulation (EU) No 37/2010 Maximum Residue Limits (MRLs) for 7 penicillins in food of animal origin were established.

Next to the ß-lactam antibiotics, in veterinary medicine, streptomycin is one of the mostly used antibiotics for the treatment of mastitis. Residues of streptomycin may therefore occur in food of animal origin, if the withholding period is not obeyed or if it is used improperly.

In high concentrations, streptomycin leads to ototoxic and nephrotoxic effects. The chronic exposure of humans with low concentrations, as found in food, may cause allergies, impair the intestinal flora and induce resistance of pathogenic microorganisms. To protect the consumer against healthy risks and avoid food-technological problems, a sensitive and simple method for the detection of streptomycin is necessary. The EU-regulations for streptomycin are specified in MRLs (maximum residue limits) for meat and milk (muscle and liver: 500 ppb, kidney: 1000 ppb, honey: 10 ppb and milk: 200 ppb).

Sulfonamides are widely used as feed additives, mainly for fattening of calves and pigs. Combined with inhibitors of dihydrofolate reductase such as trimethoprim, tetroxoprim, or pyrimethamine sulfonamides are also used in veterinary medicine for the treatment of intestinal infections, mastitis, pulmonitis and other (systemic) diseases. Sulfonamide residues may therefore occur in food of animal origin such as meat and milk. Particularly the transmission of the carcinogenic sulfamethazine represents a threat to human health. According to the EU law, a maximum residue limit (MRL) for all substances of the sulfonamide-group of 100 µg/kg (ppb) in muscle, fat, liver and kidney and of 100 µg/l (ppb) in milk is valid

In 1948, aureomycin (chlortetracycline) was isolated by Duggan as a metabolite of the actinomyces species Streptomyces aureofaciens. This was the first antibiotic substance of the group of tetracyclines.

Worldwide, tetracycline, chlortetracycline and oxytetracycline are authorized for veterinary use. Therefore, health risks for the consumer can occur. In all animal species which are used for food production, tetracycline residues (the sum of mother substance and the 4-epimer) are limited in the EU law, commission regulation (EU) No 37/2010 with the following limits (MRLs): 100 ppb in muscle and in milk. The RIDASCREEN® Tetracyclin test can be used to detect tetracycline in milk and dairy products (cheese, butter, curd, yoghurt, kefir, cream, sour cream), meat and meat products as well as seafood, egg and honey.