Testing for Antibiotics in Dairy: Multi- vs. Single-class Methods

Introduction

According to the World Health Organization (WHO), antimicrobial resistance is one of the most serious threats to global public health today. The misuse and overuse of antibiotics in both humans and in animal production has been a major cause of this growing resistance, resulting in a number of regulatory bodies placing stringent restrictions on their use in food-producing animals.

From the dairy farm to the processing plant, raw milk is tested multiple times for the presence of antibiotics. This ensures that any drug residues are below established tolerance levels and that any potential harm to human health is minimized.

Antibiotic residues in milk also pose an economic risk to the dairy industry. Antibiotics inhibit biotechnological production processes involving microorganisms, such as starter cultures for fermented products. A range of methods have been developed to rapidly test dairy products for the presence of antibiotics.

These tests are available as either a single-class method, which detects the presence of antibiotic drug residues from one family or ‘class’ of drugs, or as a multi-class method. Multi-class tests will detect the presence of antibiotics from a range of different drug classes, such as beta-lactams, sulphonamides and tetracyclines. For single- and multi-class analysis, PerkinElmer offers a comprehensive range of rapid testing solutions to help those in the dairy industry quickly and efficiently verify the safety of their products.

Rapid testing for beta-lactams

PerkinElmer offers two strip tests for the detection of beta-lactams, which are the most commonly used antibiotics around the world - penicillin being the best-known example. The AuroFlow™ Beta-lactam Strip Test Kit uses a simple two-step protocol for the detection of beta-lactams in milk. Raw or chilled milk is mixed with the reagent and because this test can be performed at room temperature, it can be used on farm, as tankers arrive at the plant or in the lab. This qualitative, lateral flow assay can detect 14 beta-lactam antibiotics.

The second beta-lactam test doesn’t require a mixing step but does necessitate an incubator. The AuroFlow^™ PR1ME^™ Beta-lactam MRL Assay enables the detection of beta-lactams at or below EU and CODEX maximum residue limits (MRLs). This test is often the preferred method for lab-based users as the one-step method reduces manual labor. As such, this method can improve dairy quality control efficiency.

Using a digital reader to interpret the results from rapid test strips can eliminate any ambiguity and provide users with a clear positive or negative result. The QuickSTAR^™ Strip Reader is a handheld, portable device that works across the range of rapid strip tests provided by PerkinElmer. This device produces a result within seconds and will store images of the strip enabling traceability of results.

Single-class ELISA test kits

Another tool used for single-class analysis of antibiotics in animal-derived products are enzyme-linked immunosorbent assays (ELISAs). These immunochemical methods offer a rapid, sensitive and cost-effective protocol for the low-level detection of drug residues in dairy products. They have the added benefit of enabling routine quantitative analysis of large numbers of samples. ELISA tests may be used to detect the presence of specific drugs or very low drug concentrations without having to invest in more expensive analytical equipment or extensive training for staff.

A variety of single-class test kits are available for detecting beta-lactams, chloramphenicol, fluoroquinolones, sulphonamides and tetracyclines. The MaxSignal^® ELISA test kits deploy a competitive enzyme immunoassay providing high sensitivity, reproducibility and recovery rates. Results are typically analyzed using a microplate reader and quantitative results can also be produced by comparing the color intensity of unknown samples with a standard curve.

One example is the MaxSignal^® Chloramphenicol ELISA test, which shows considerable advantages over the traditional radioimmunological or gas chromatography techniques. Moreover, this ELISA test no longer requires the use of radioactive materials, in addition to be more cost efficient when compared to gas chromatography.

Multi-class tests

Single-class methods are straightforward to perform due to the similarity of the structural and chemical properties of drugs within the same family. However, with the high number of regulated veterinary drugs, multi-class methods improve efficiency dramatically by detecting of a variety of drugs in a single test.

PerkinElmer offers a range of rapid, multi-class methods for the detection of multiple antibiotic drug classes in a single procedure. For example, beta-lactam, tetracycline and sulphonamide antibiotic residues can be detected in raw commingled cow’s milk using the AuroFlow^™ BTS Combo Strip Test.

Similar to the single-class methods, these tests are designed for use in the field, with the two-step method, or in the lab, utilizing the one-step method. This specific kit can detect a higher number of antibiotics at or below defined MRLs compared to any other competitor kit.

Mitigating risk throughout the chain

Rapid testing solutions for the detection of antibiotics in dairy are put in place to comply with regulations, protect the dairy industry from expensive mistakes and ultimately to ensure the safety of consumers. With simple to use methods that can be deployed just about anywhere, testing at all appropriate points along the supply chain is possible.