Evaluation of the Charm maximum residue limit beta-lactam and tetracycline test for the detection of antibiotics in ewe and goat milk

Abstract

The Charm maximum residue limit P-lactam and tetracycline test (Charm MRL BLTET; Charm Sciences Inc., Lawrence, MA) is an immunoreceptor assay utilizing Rapid. One-Step Assay lateral flow technology that detects P-lactam or tetracycline drugs in raw commingled cow milk at or below European Union maximum residue levels (EU-MRL). The Charm MRL BLTET test procedure was recently modified (dilution in buffer and longer incubation) by the manufacturers to be used with raw ewe and goat milk. To assess the Charm MRL BLTET test for the detection of beta-lactams and tetracyclines in milk of small ruminants, an evaluation study was performed at Instituto de Ciencia y Tecnologia Animal of Universitat Politecnica de Valencia (Spain). The test specificity and detection capability (CC beta) were studied following Commission Decision 2002/657/EC. Specificity results obtained in this study were optimal for individual milk free of antimicrobials from ewes (99.2% for beta-lactams and 100% for tetracyclines) and goats (97.9% for beta-lactams and 100% for tetracyclines) along the entire lactation period regardless of whether the results were visually or instrumentally interpreted. Moreover, no positive results were obtained when a relatively high concentration of different substances belonging to antimicrobial families other than beta-lactams and tetracyclines were present in ewe and goat milk. For both types of milk, the CC beta calculated was lower or equal to EU-MRL for amoxicillin (4 mu g/kg), ampicillin (4 mu g/kg), benzylpenicillin (<= 2 mu g/kg), dicloxacillin (30 mu g/kg), oxacillin (30 mu g/kg), cefacetrile (<= 63 mu g/kg), cefalonium (<= 10 mu g/kg), cefapirin (<= 30 mu g/kg), desacetylcefapirin (<= 30 mu g/kg), cefazolin (<= 25 mu g/kg), cefoperazone (<= 25 mu g/kg), cefquinome (20 mu g/kg), ceftiofur (<= 50 mu g/kg), desfuroylceftiofur (<= 50 mu g/kg), and cephalexin (<= 50 mu g/kg). However, this test could neither detect cloxacillin nor nafcillin at or below EU-MRL (CC beta >30 mu g/kg). The CC beta for tetracyclines was also lower than EU-MRL for chlortetracycline (ewe milk: <= 50 mu g/kg; goat milk: 75 mu g/kg), oxytetracycline (<= 50 mu g/kg), and tetracycline (<= 50 mu g/kg). Regarding the 4-epimers of these tetracyclines only 4-epioxytetracycline was detected by the Charm MRL BLTET test below EU-MRL (ewe milk: 75 mu g/kg; goat milk: <= 50 mu g/kg). Acidiol had no effect on the performance of the test. The Charm MRL BLTET test could be used routinely with adapted test procedure for the fast screening of ewe and goat milk.