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Development and Validation of a Screening Protocol for Identifying Sulfamethazine-Violative Swine Carcasses at Ontario Abattoirs Using the CHARM ROSA <sup>TM</sup> Sulfamethazine Test


The CHARM ROSA (Rapid One Step Assay) Sulfamethazine (SMZ) Test for milk was adapted to urine and compared to the Sulfa On Site Test (SOS) to examine the suitability of using the ROSA as an alternative to the SOS. The SOS is a thin layer chromatographic method widely used in North American abattoirs for screening porcine urine samples for SMZ residues. The ROSA sulfamethazine test is a lateral flow test strip currently marketed for screening milk. A suitable urine dilution buffer and protocol was developed to adapt the ROSA test to urine testing. Two dilutions were determined to adjust test sensitivity to urine target levels, 1:150 for 0.4 ppm SMZ (corresponding to violative SMZ levels in the liver tissue) and 1:600 for 1.3 ppm SMZ (corresponding to violative SMZ levels in muscle tissue). The concentration response of the dilution schemes were determined using fortified urine samples and demonstrated 90% sensitivity (ie. positive) with 95% confidence via probit analysis at the 0.252 ppm and 1.033 ppm SMZ urine levels. Meat inspectors at an Ontario abattoir field tested a two-tiered ROSA testing model that screened at the 0.4 ppm level, for condemnation of violative offal, with subsequent confirmation of positive urines at the 1.3 ppm level to predict tissue positive carcasses. Results were compared to the SOS test results of 294 urine samples. Comparative tables showed that relative to the SOS test the ROSA test had sensitivity and negative predictive values of 100% at the 0.4 ppm and 1.3 ppm SMZ target levels. The test specificity (ie. negative) was 86% at the 0.4 ppm target level and 96% at the 1.3 ppm target level. TLC/densitometry confirmatory analysis of 1:600 dilution positive samples found liver violative levels in 2 samples, non-violative levels in 13 samples and not detected in 1 sample. TLC/densitometry on 13 of the 16 corresponding positive muscle tissue samples found SMZ residues at violative levels in 1 sample, non-violative levels in 8 samples and not detected in 4 samples. These results indicate that the CHARM ROSA SMZ test using a 1:600 dilution may be reliably used for screening porcine urine for SMZ residues in abattoirs. Greater dilutions of urine may be necessary to more closely predict organ and tissue violative levels.

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Expected Impact of Project Outcomes on Food Safety in Ontario: The application of the new method will eliminate the need to hold non-violative carcasses overnight or longer while waiting for laboratory test results, thereby freeing up storage space at the abattoirs and hastening the transfer of product to market. It will demonstrate environmental responsibility and concern for HACCP violations by removing the need for a laboratory method that utilizes toxic solvents requiring expensive disposal practices, as well as the use of glass capillary tubes. The new method is much simpler to perform decreasing the chance for testing errors. <P> For more information, please visit the <a href="; target="_blank">Ontario Ministry of Agriculture, Food & Rural Affairs (OMAFRA) Food Safety Research Program</a>.

Mitchell, Mark
University of Guelph
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