Choosing the Right Antibiotic Testing Method for Dairy: Rapid, Semi-Quantification or Full Quantification

Introduction

Across the dairy value chain, farmers, dairy processors and regulatory authorities must work together to avoid unsafe levels of antibiotics in their milk product. This involves various types of tests at various points throughout dairy production and the supply chain.

Knowing which antibiotic test to use, and when, can be a challenging decision with multiple opposing factors - from the need to comply with local regulations to the pressure to be as fast as possible. Stakeholders in the supply chain must select between rapid test, semi-quantification or full quantification methods in order to ensure the milk product’s quality as it travels from the farm to the final product.

“Get Well Soon”

Whenever dairy cows are treated with antibiotics, they are taken out of milking rotation to conserve the overall integrity of the farm’s milk product. Of course, every day a cow is pulled out of milking rotation is a financial loss to the farmer, creating an urgency to get the cow “back to work” as soon as possible.

Unfortunately, without rigorous testing procedures in place, there is a risk that these cows are returned to production too soon – and their tainted milk enters the commercial market. Farmers need highly reliable, easy-to-use methods of testing milk to understand when an antibiotic has been completely eliminated from the cow’s system.

“Hey honey, does this milk smell funny?”

When milk is picked up from a dairy farm, it is often combined with other farms’ milk into a single tanker. Clearly, the production efficacy of processing one large batch can be compromised from potential antibiotic contamination from a single cow.

In order to mitigate and uncover a potential contamination source, processing companies hold back samples of milk from each individual farm. If testing on the whole tanker indicates unsafe levels of antibiotics, these samples can be readily tested and the antibiotics can be traced back to the source of the contamination.

The need for speed

Rapid, high-throughput screening methods can occur at different stages of the milk product’s journey:

• On the farm
• On the truck
• At regional borders
• At delivery
• Pre-processing at the plant

Each check point will have its own unique attribute e.g. testing on trucks requires tools that use minimal space, are hand-held, and are battery operated.

Whenever – or wherever – contamination is suspected, milk can be analyzed with high-sensitivity instruments to deduce the precise antibiotic contaminants and their concentrations, which can shine light on how and where mistakes occurred.

Ironically, regulations are not homogenized.

The rapid testing applied at farms and processing plants may be sufficiently sensitive for screening at the maximum residue levels (MRLs) of antibiotics, however the lack of global standard harmonization means that certain rapid tests are unsuitable in certain regions. Several national and international organizations set MRLs of antibiotics in milk differently.

For instance, the EU has regulations that require the detection of 15 different ß-lactam antibiotics at different thresholds to the 6 ß-lactams that the USA regulates. The standards laid out in the UN’s Codex Alimentarius are different again, and even countries that generally follow international standards may have some exceptions for specific antibiotics.

The result of these conflicting regulations is that businesses in the dairy value chain must maintain constant awareness about where their product is being transported and ensure that they have the appropriate testing in place to comply with local regulations wherever they operate.

Rapid testing

Digital readers make up an important component of supply chain transparency and traceability. Beyond the obvious “rapidness” of rapid testing, images of the test strips should be uploaded to a dairy’s quality management system, providing documentation of product quality needed during audits and inspections. In addition to storing results, digital readers also minimize human error. For instance, in the case where a milk producer and a milk transporter are in disagreement between the visual results of an antibiotic test, digital readers remove this ambiguity and provide a documented, reliable reading.

For manufacturers of fermented dairy products such as sour cream and yogurt, it is important to verify the quality of the milk they purchase. Many of their processes, and certainly their final products, deliberately include bacterial cultures, and it is imperative that no antibiotics are present that may compromise these delicate ecosystems. Strip test kits are available that can determine the presence of over twenty major antibiotics and are deployed to verify incoming milk quality prior to the fermentation processes. These simple tests require no scientific expertise and can give peace of mind to manufacturers of milk-based products.

Semi-quantitative testing

In certain circumstances, where regulations define tighter thresholds of a single antibiotic, or other cases where concentrations of all individual antibiotics are required, semi-quantitative ELISA-based screening methods can provide the right solution. Immunoassays coupled with automated plate readers can provide a high throughput method for investigating whole groups of antibiotic families in milk over a wide dynamic range.

In this technique, milk samples are first placed on a plate that is coated with antibiotic-specific antibodies. By scanning the plate in a spectroscopy-based plate reader, milk testers can measure fluorescence and generate standard curves for the concentrations of different antibiotics in the samples.

Generally, positive results identified using these methods will still need to be confirmed with high-sensitivity analysis, but it remains the quickest and most inexpensive method for measuring concentrations of specific antibiotics in milk.

An important consideration in standard ELISA protocols is the manual labor requirements and resulting impact on throughput. This is a crucial factor to consider in food testing laboratories that are often overrun with samples. Reducing hands-on experimental time with faster sample preparation protocols and automated microplate readers should be a consideration when assessing ELISA protocols for antibiotic testing.

Fully quantitative testing

If routine rapid testing – or even semi-quantitative testing – identifies antibiotic contamination at any point in the dairy supply chain, it must be further investigated using fully quantitative analytical methods such as liquid chromatography tandem mass spectrometry (LC/MS/MS).

These analytical techniques require more space than rapid testing methods, have longer run-times and are more expensive, but they are unparalleled in the accuracy to which they can determine analyte concentrations. LC/MS/MS represents the most reliable way to identify and quantify antibiotics in the dairy supply chain and is a critical tool for contract testing laboratories and central food agencies.

Testing milk and milk products with LC/MS/MS may also be needed within countries that set extremely low MRLs for specific antibiotics or even Minimum Required Performance Limits (MRPLs) for banned drugs. In these cases, rapid testing with strips or ELISA methodologies are often not sufficiently sensitive to confirm regulatory compliance, and so testing must be outsourced to contract laboratories for analysis.

As an additional advantage to central food testing labs, these instruments can also measure drug metabolites and additional analytes, such as aflatoxins and pesticides, in the same test.

Conclusion

The most appropriate test for antibiotics in dairy products depends on the specific needs of the testing site. It is therefore imperative that different facilities have a broad understanding of exactly why they are running certain tests and what results they need.

Wherever milk is tested for antibiotics, rapid, semi-quantitative and fully quantitative methods will all have their own case-specific advantages and disadvantages. Deciding which method is appropriate depends on the user expertise, the space available, and the accuracy and speed required. When the right solutions are implemented at every point in the value chain, it makes the daunting task of antibiotic testing more efficient and much more reliable. This is important not only to ensure compliance with regulations and prevent unintentional food fraud, but also to maintain consumer trust and mitigate the risk of harm to public health.