Submitted to: Association Official Analytical Chemists Annual Intrl Meeting & Exposition
Publication Type: Abstract Only
Publication Acceptance Date: June 25, 1998
Publication Date: N/A
Antibiotic residues can be detected in animal tissues by a variety of screening tests based on microbial inhibition. In the seven-plate assay used by USDA's Food Safety and Inspection Service (FSIS), penicillinase is incorporated in all but one plate in order to distinguish the B-lactam group of antibiotics from other types. However, B-lactams such as cephalosporins, cloxacillin, and ceftiofur metabolites are resistant to degradation by penicillinase and may not be identified as B-lactams by this procedure. They thus may be classified as unidentified microbial inhibitors (UMIs). These resistant compounds can be degraded by other B-lactamases. The present study describes the use of an improved screening test protocol to identify any B-lactam antibiotics classified as UMIs. A multiresidue HPLC procedure based on a method previously described for B-lactams in milk was also used to identify and quantitate residues. These approaches were tested with 24 samples from FSIS classified as containing UMIs. Of these, three contained penicillin G, one at a violative level, and five contained a metabolite of ceftiofur. The others were negative for B-lactam antibiotics.