Validation of BetaXpress Milk

The BetaXpress Milk (Unisensor s.a., Wandre, BE) is a competitive receptor test for the rapid screening of residues of ß-lactams (penicillins and cefalosporins) in raw milk. The time to result for the assay is approximately 3 minutes (two incubation steps of 90 seconds).

This new test was validated at ILVO-T&V (Technology & Food Science Unit of the Institute for Agricultural and Fisheries Research of the Flemish Community) according to Commission Decision 2002/657/EC and to the CRL (Community Reference Laboratories) guidelines for the validation of screening methods for residues of veterinary medicines (Anonymous, 2010). The following analytical parameters were checked: test specificity, detection capability, and test robustness (impact of deviation of the test protocol impact of the milk composition, and batch differences of reagents). Further the suitability of the BetaXpress Milk to screen different milk types (UHT milk, sterilized milk, reconstituted milk powder, thawed milk) or milk from animal species other than the cow (goat, ewe, and mare) was also tested. Finally, the test was integrated in the monitoring of dairy samples to check the occurrence of false negative or false positive results, and the test was also included in a national ring trials.

The test was very specific; no interaction was noticed by compounds of antibiotic families or chemotherapeutics other than ß-lactams except for the interference by clavulanic acid. All ß-lactams with a Maximum Residue Limit (MRL) in milk were at least in 95% of the replicates detected at their respective MRL except for nafcillin (MRL=30 µg/kg; ccß=100 µg/kg) and cephalexin (MRL=100 µg/kg; ccß=900 µg/kg). The detection capability for ?-lactam antibiotics of the BetaXpress Milk is comparable to the detection capability of the TwinSensor Milk on the ß-lactam channel (Reybroeck & Ooghe, 2010).

The repeatability of the reader and the test were very good. The test result remained reliable even when delaying the reading or using not the correct volume of milk or testing milk of different temperature. Also, the impact of milk parameters (somatic cells, total bacterial count, fat and protein content, pH) was tested as part of the robustness testing. No interference by these milk parameters was noticed except for milk with a high fat content, giving a false positive result for blank milk. No significant differences were noticed in detection capability of benzylpenicillin for different milk types (raw milk, UHT-milk, sterilized milk, reconstituted milk powder, or thawed milk) and other species animal milk (goats’, mares’, or ewes’ milk). Therefore, BetaXpress Milk offers the flexibility of testing all different milks. The detection capability of cefquinome was somewhat hampered in heat-treated milk and in ewes’ and mares’ milk. No significant differences in detection capability were found between three different batches of reagents of BetaXpress Milk. Correct BetaXpress Milk results were obtained in two ring trials.

Out of the data of this validation study it can be concluded that the BetaXpress Milk is a very fast, simple, and reliable test for the control of residues of ß-lactam antibiotics in tanker milk at the entrance. The test could also be used at farm level in order to prevent tanker milk contamination. The test is also giving reliable rest results for different milk types and milk of animal species different from the cow (goat, ewe, mare).