Evaluation of the swab test on premises for detection of antimicrobial residues in bovine and porcine kidneys.

The effect of sample matrix on the sensitivity of the Swab Test On Premises (STOP) was evaluated for selected antimicrobials. Fluid was extracted from bovine and porcine kidneys, and fortified with known levels of drugs. Aqueous standards were also prepared at the same levels. An aliquot of the fortified fluid or water was pipeted onto a dry swab which was placed onto the surface of a STOP plate, and the plate was incubated as outlined in the test kit manual. Zones of bacterial growth inhibition were measured and recorded, and additional testing was performed with decreasing levels of drug until a minimum detectable level was determined. The effect of temperature on the sensitivity of the test was also evaluated by running samples in duplicate, one set at a nominal temperature of 28 degrees C, and the second set at a nominal temperature of 32 degrees C. Fortified bovine kidney fluid produced significantly larger zones than did porcine kidney fluid at both temperatures, but the mean zone sizes for fortified water were not significantly different from those of bovine or porcine kidney fluid at either temperature. For all 3 matrixes, zones of inhibition were significantly larger at 28 degrees than 32 degrees C.

Determination of sulfonamide residues in the tissues of food animals using automated precolumn derivatization and liquid chromatography with fluorescence detection.

A liquid chromatographic method for the determination of sulfachloropyridazine, sulfadiazine, sulfadimethoxine, sulfadoxine, sulfaethoxypyridazine, sulfamethazine, sulfaquinoxaline, and sulfathiazole residues in the muscle, liver, and kidney of food animals using sulfapyridine as internal standard is reported. Tissues are extracted using a modified version of AOAC Official Method 983.31 (Sulfonamide Residues in Animal Tissues). The sample extract is reconstituted in pH 3.0 buffer-acetonitrile (60 + 40) and filtered into an autosampler vial. Using a programmable autosampler of a liquid chromatograph, a portion of the sample is derivatized precolumn with fluorescamine. The sulfonamide derivatives are separated by liquid chromatography using a C18 column with a mobile phase of 0.02M phosphoric acid-acetonitrile (60.5 + 39.5) and detected by fluorescence (excitation, 405 nm; emission, 495 nm). The method was applied to swine and cattle muscle, liver, and kidney; sheep and horse muscle and kidney; and chicken muscle and liver. The mean values for samples fortified with sulfonamides at levels between 0.05 and 0.2 microg/g agreed within 96-99% of spiked levels, with coefficients of variation ranging from 4-10%. The limit of detection (LOD) for all sulfonamides was 0.01 microg/g, with the exception of sulfaquinoxaline, for which the LOD was 0.015 microg/g.

Laboratory Testing of the Charm Test II Receptor Assays and the Charm Farm Test with Tissues and Fluids from Hogs Fed Sulfamethazine, Chlortetracycline, and Penicillin G.

The potentials of the Charm Test II receptor assays for the detection of residues of sulfonamides, tetracyclines, and ß-lactams and the Charm Farm Test for screening for antimicrobial residues were tested. Market hogs were fed rations containing three times the label level of sulfamethazine, chlortetracycline, and penicillin G for 2 weeks. Groups were killed after 0, 2, 4 and 8 days of withdrawal. Quantitative chemical methods were used to determine residue levels in fluids and tissues. Results were compared with those obtained using the qualitative Charm Test II receptor assays and the Charm Farm Test antimicrobial inhibition assay. For the Charm Test II assays for sulfonamides, tetracyclines and ß-lactams, respectively, 1.6, 5, and 6% of the results were false positive and 7, 5, and 0% were false negative, based on the limits of detection for the test kits and the quantitative results. On a similar basis for the Charm Farm Test, 16% of the results were false positive (6 kidney, 4 muscle, and 6 urine samples) and 1% were false negative (sulfamethazine in one urine sample).

Laboratory Evaluation of the Charm Farm Test for Antimicrobial Residues in Meat.

Charm Farm Tests were applied to 54 muscle and 44 kidney bovine samples, and 95 muscle and 90 kidney porcine samples collected for Canada's national meat inspection program from animals suspected of containing antimicrobial residues. The assays were run in conjunction with Agriculture and Agri-food Canada's routine confirmation analyses for suspect samples collected at federally inspected packing plants. When the bovine and porcine results were combined, 19% of the kidney and 8% of the muscle results were false negatives. Using the Charm Farm Test to screen only the kidney samples would have resulted in 100% identification of the muscle samples that were found to contain violative levels of drug residues. One percent of the kidney and 16% of the muscle results were false positives, on the basis of the results of the confirmatory tests. Minimum detectable levels found in fortified (i.e., artificially contaminated) muscle and kidney with the Charm Farm Test for ceftiofur, chlortetracycline, oxytetracycline, tetracycline, erythromycin, gentamycin, neomycin, penicillin G, streptomycin, sulfamethazine, sulfadimethoxine, tylosin, tilmicosin, and trimethoprim were similar to those claimed by the manufacturer. Minimum detectable levels for the Charm Test II (dihydro) streptomycin and erythromycin receptor assays are reported for fortified muscle and kidney to provide an indication of the relative sensitivities of the Charm Farm Test and the Charm II Tests for these compounds. To further assess the Charm Farm Test's potential as a replacement for existing tests in packing plants, parallel testing needs to be conducted on fresh tissues in a plant environment.