Evaluation of the Swab Test On Premises for Detection of Antimicrobial Residues in Bovine and Porcine Kidneys

Abstract

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.