Detection of residues of tetracycline antibiotics in pork and chicken meat: Correlation between results of screening and confirmatory tests

Residues of the tetracycline group of antibiotics were quantified in pork a nd chicken muscle tissue that had previously been screened with a microbiol ogical inhibition test and an immunological method. Pieces of frozen pork a nd chicken meat were screened on a pH 6 culture medium seeded with Bacillus subtilis. An aqueous extract of the inhibitor-positive samples was then sc reened with a group-specific commercial ELISA kit, able to detect levels of oxytetracycline, chlortetracycline, tetracycline and doxycycline correspon ding with the European MRL or lower. The cut-off value of the ELISA was set at a B/B-0 value of 75%. Finally, confirmation and quantification were per formed using a validated HPLC method with fluorescence detection. The fluor escence was induced by complexation of the tetracyclines with the zirconium cation which is added post-column to the HPLC eluate. This fluorescence ma kes it possible to quantitate residues below one-half of the MRL. To gain a dditional qualitative information some samples were also analysed with LC-M S-MS. ELISA analysis demonstrated the presence of residues of tetracyclines in 12 out of 19 inhibitor-positive pork samples and in 19 out of 21 inhibitor-po sitive chicken samples. Doxycycline was detected with HPLC in 10 of these 1 2 pork samples and in 18 out of 19 chicken samples. The two other ELISA pos itive pork samples contained oxytetracycline, while no tetracyclines were f ound in one ELISA positive chicken meat sample. The correlation between the ELISA B/B-0 values and the actual levels determined with the HPLC method w as poor, whereas a better correlation was observed between the inhibition z ones and the doxycycline levels. Our results indicate that an inhibition te st with a medium at pH 6 and B, subtilis as test organism is well suited to screen pork and chicken muscle tissue for residues of tetracycline antibio tics. Since many positive samples contained doxycycline levels below the MR L, a confirmatory method is necessary to quantify the residues.