Validation of a wide-spectrum microbiological tube test, the EXPLORER® test, for the detection of antimicrobials in muscle from different animal species

Abstract

Explorer® is a simple and fast new kit for the detection of inhibitory substances in raw meat. The test, a 96-well microtitre plate, is based on the inhibition of microbial growth (Geobacillus stearothermophilus spores). It was validated in accordance with European Commission Decision 2002/657/EC (2002). The specificity and detection capabilities for five compounds from major antimicrobial families and robustness were studied. The specificity of the test was assessed with four different animal species and was found to be very satisfactory (false-positive rates lower than 10%). The detection capabilities for amoxicillin (10 µg kg⁻¹) and tylosin (100 µg kg⁻¹) were at the maximum residue limit (MRL) level (50 and 100 µg kg⁻¹, respectively) for both, for doxycycline (200 µg kg⁻¹) and sulfathiazole (200 µg kg⁻¹) at twice the MRL (100 µg kg⁻¹ for each) and for cefalexin (500 µg kg⁻¹) at 2.5 times the MRL (200 µg kg⁻¹). Twenty-one samples were analysed in parallel with the Four Plate Test, the STAR protocol and the Explorer® test. One false-positive result and two false-negative results (samples containing oxytetracycline) were reported with the Explorer® test. In conclusion, the Explorer® test was shown to be robust and easily automated. Photometric reading allows informatic data storage and objective readings between technicians and days. The test can be used as a wide screening test because it enables detection of most of the antimicrobial families (penicillins, cephalosporins, tetracyclines, sulphonamides, and macrolides) in muscles from different animal species (porcine, bovine, ovine, poultry).

Keywords:

• in-house validation
• inter-laboratory validation
• method validation
• screening–microbial screening
• residues
• veterinary drug residues
• veterinary drug residues–antibiotics
• veterinary drug residues–antimicrobials
• animal products–meat
• meat

Acknowledgements

Thanks to Zeu-Inmunotec (Saragossa, Spain) for providing the authors with different batches of the Explorer® test.