54I-10 |
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M. B. MEDINA, Microbial Biophysics and Residue Chemistry and Core Technologies Research Unit, USDA-ARS-Eastern Regional Research Center, 600 E. Mermaid Ln., Wyndmoor, PA 19038-8598 Beta-lactams are commonly used as antimicrobial drugs to treat or prevent infectious diseases. Antibiotic residues above tolerance levels are not allowed in foods of animal origin. In USDA's monitoring system, animal tissues determined positive for antibiotic residues at the slaughterhouses are further assayed with the 7-plate microbial inhibition assays. This assay cannot identify the violative ceftiofur metabolites. We have developed and reported a screening approach to differentiate the penicillin and cephalosporin b-lactams through the selective hydrolysis of b-lactams with Type I and Type II lactamase. Our current study adapted this method to screen for the b-lactams in 30 bovine kidney tissues containing incurred residues, and in over 30 spiked tissue extracts. The kidney tissues were extracted with phosphate buffer and hydrolyzed with Penase and Lactamase II. The hydrolyzed samples were tested with a microbial inhibition assay (Delvotest P Mini) and enzyme-based assays (SNAP and Penzyme). The results showed that the incurred b-lactams were qualitatively (+/-) detected before hydrolysis and were in agreement with the standard 7-plate assay. The ceftiofur metabolites were also detected in samples containing unidentified microbial inhibitors (UMI). The microbial inhibition assay showed better agreement with the LC/MS/MS than with the use of the commercial enzyme-based screening assays. The combined selective hydrolysis and microbial inhibition assay detected the desafuroylceftiofur cysteine at violative tissue levels of 1 to 8 mg/mL (ppm), and these results correlated with the confirmatory LC/MS/MS analysis. The Penase/Lactamase II screening approach can be used to validate the presence of UMI or suspect ceftiofur metabolite prior to LC/MS/MS analysis. This test is rapid, simple, and inexpensive where the sample preparation, hydrolysis, and testing can be carried out in less than 4 hr, compared to the 7-plate assay which takes 16 to 18 hr.
Session 54I, Toxicology & Safety Evaluation: General
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |