A study of the origin of chloramphenicol isomers in honey

Due to the unexpected detection of chloramphenicol isomer residues in honey, we have studied the hypothesis of unauthorized or unintended use of unregistered veterinary drug preparations. First, we have investigated honey samples in which a discrepancy was observed between the results of the immunological screening methods and the confirmatory liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. In all samples, previously identified to be contaminated with the banned antibiotic chloramphenicol according to LC-MS/MS only, the presence of dextramycin (SS-para isomer of chloramphenicol) was detected by chiral LC-MS/MS. The source of dextramycin in honey was investigated by studying the preparations utilized in apiaries from which the above non-compliant honey samples have been received. In all these preparations (beehive strips applied against the mite Varroa destructor) chloramphenicol was detected in the concentrations ranging from 33 to 34,400 μg kg-1. Chiral LC-MS/MS demonstrated the presence of chloramphenicol and dextramycin in different ratios, and it was concluded that these preparations can be the source of chloramphenicol and dextramycin residues in honey. These preparations were of foreign production and are not officially registered in accordance with current legislation.