Antibiotics in milk: causes and methods of detection

Milk is an essential food, rich in proteins, fats, carbohydrates, vitamins, and minerals. However, its quality can be compromised by the presence of undesirable substances, such as antibiotics. The presence of antibiotic residues in milk raises serious concerns among consumers, as they can lead to allergic reactions, disrupt gut microbiomes, and contribute to the development of antibiotic resistance in humans. Therefore, it is crucial to understand the causes of antibiotics in milk and know effective methods for detecting them.

Reasons for the appearance of antibiotics in milk

The main reasons why antibiotics may appear in milk are:

• Treatment of animal diseases: Antibiotics are widely used in veterinary medicine to treat bacterial infections in dairy animals, such as mastitis , pneumonia, enteritis, and others. After administration, some of the drug's metabolites are excreted from the animal's body in milk.
• Prophylactic use: In some cases, antibiotics may be used to prevent disease, especially in crowded livestock conditions.
• Violation of withdrawal periods: Each antibiotic has a so-called "withdrawal period," during which milk from treated animals cannot be used for food or processing. If milk from such animals is collected before this period has passed, it becomes contaminated with antibiotics.
• Milking errors: Using the same milking equipment for healthy and treated animals without proper cleaning and disinfection can lead to cross-contamination of milk.
• Use of feed containing antibiotics: Although less common, antibiotic residues can enter milk through feed if it contains antibacterial additives not intended for dairy cattle or was used improperly.

Methods for detecting antibiotics in milk

To ensure the safety of dairy products, various methods have been developed to detect the presence of antibiotics in milk. These can be divided into several categories:

• Rapid tests (quick tests ):
  • Microbiological inhibitor tests: These are based on the sensitivity of specific bacterial strains to antibiotics. If antibiotics are present in milk, bacterial growth is inhibited, which is indicated by a color change in the indicator. These tests are quick, relatively inexpensive, and can detect the presence of broad-spectrum antibiotics. Examples: Delvotest, Charm MRL.
  • Enzyme-linked immunosorbent assays (ELISA) and immunochromatographic tests (test strips): These use antibodies to specifically bind to antibiotic molecules. The result is usually indicated by a color change. These tests are highly specific and sensitive to certain groups of antibiotics, providing rapid results.
• Laboratory methods:
  • High-performance liquid chromatography with mass spectrometry (HPLC-MS): This is the "gold standard" for the accurate quantification and identification of a wide range of antibiotics. This method is highly sensitive and specific, but requires expensive equipment and qualified personnel.
  • Thin layer chromatography (TLC): A less sensitive and more labor-intensive method, but can be used to screen for certain groups of antibiotics.
  • Gas chromatography with mass spectrometry (GC-MS): Also used for the analysis of some groups of antibiotics after appropriate derivatization.
  • Biological methods (long-term microbiological tests): Longer versions of inhibitor tests, often used to confirm rapid test results or to detect residues that may not be detected by rapid methods.

Conclusion

Monitoring antibiotic levels in milk is a critical aspect of food safety. Regular milk testing at all stages of production, from the farm to the processing plant, prevents contaminated products from reaching the shelves. Adherence to regulations on the use of veterinary drugs and withdrawal periods, as well as the implementation of modern and effective control methods, such as rapid tests for initial screening and laboratory methods for confirmation, help maintain the high quality and safety of dairy products for consumers.