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.

Evaluation of the Swab Test on Premises, the Calf Antibiotic and Sulfa Test, and a Microbial Inhibitor Test with Standard Solutions of 22 Antibiotics.

The sensitivities of the Swab Test on Premises (STOP), the Calf Antibiotic and Sulfa Test (CAST) and a laboratory Microbial Inhibitor Test (MIT) previously used for confirmation of STOP results were compared. Different media were compared for the STOP and MIT. The CAST was more sensitive than the STOP for the 22 antibiotics tested. The sensitivity of the STOP procedure increased for 15 of the 22 antibiotics tested when the standard STOP medium, Antibiotic Medium No. 5 (AM-5), was replaced with Saskatoon Antibiotic Medium-3 (SAM-3), the medium used for thin-layer bioautography. When Antibiotic Medium No. 2 (AM-2) was used in the STOP procedure, the overall sensitivity was intermediate between that obtained using AM-5 and SAM-3. For the MIT, Micrococcus luteus ATCC 9341 provided greater sensitivity as a test organism than Bacillus cereus ATCC 11778 for 16 antibiotics and was less sensitive for 4 antibiotics, particularly chlortetracycline, oxytetracycline and tetracycline. M. luteus ATCC 9341 was notably more sensitive as a test organism for bacitracin and lincomycin than was B. cereus ATCC 11778.