Immunochemical screening for antimicrobial drug residues in commercial honey

Honey samples (n = 100; origin: various countries from Eurasia, Oceania, and the Americas) were analysed by enzyme immunoassays (EIA) for tetracyclines, streptomycin, and sulfathiazole. Considering antibody specificity, these EIAs are either quantitative (streptomycin) or qualitative (tetracyclines, sulfathiazole) tests. Honey extract purification was achieved by liquid-liquid partition (tetracyclines), and by solid phase extraction-immunoaffinity chromatography (streptomycin, sulfathiazole). Detection limits were 20 micrograms kg-1 (tetracycline equivalents), 10 micrograms kg-1 (streptomycin), and 50 micrograms kg-1 (sulfathiazole equivalents), with mean recoveries of 100-117%. A total of 42% of the samples was found positive by EIA; 25% were positive in one assay, 13% in two, and 3% were positive in all three tests. In the EIA for tetracyclines, 26% were positive, with 12 samples exceeding a level of 50 micrograms kg-1 (tetracycline equivalents). In the EIA for streptomycin, 19% were positive, with a mean concentration of 19 +/- 12 micrograms kg-1. In the sulfathiazole EIA, 16% of the samples were positive, with 13 samples exceeding a level of 100 micrograms kg-1 (sulfathiazole equivalents). However, when samples which were positive in the sulfathiazole EIA were reanalysed for sulfonamides by HPLC, no sulfa drugs could be detected. Experimental heating (40 degrees C) of honey spiked with sulfathiazole indicated that the sulfa drug(s) responsible for positive EIA results could be present a sugar derivatives.