Illegal penicillin residues were found in swine tissue samples when the Department of Agriculture implemented testing for specific beta-lactam antimicrobials in such tissues in July.
The penicillin G residues were detected in swine muscle and kidney tissues through testing by the USDA Food Safety and Inspection Service. Tissues containing such residues are now being condemned, as the Food and Drug Administration prohibits selling for human consumption any edible tissues containing any amount of penicillin.
Vivian Chen, PhD, deputy assistant administrator of the Office of Public Health Science in the FSIS, said such residues have been previously detected in samples but classified as unidentified microbial inhibitors because the previously used test was not specific enough to identify the residues. The agency didn't know what agent was inhibiting microbial growth, so no regulatory actions were taken.
About 80 of 220 swine tissue samples tested for antimicrobial residues during the first seven months of 2011 contained UMIs, Dr. Chen said.
In a June 22 chemistry laboratory guidebook update, FSIS officials announced that the agency would, effective July 2, expand its screening method for beta-lactam antimicrobials to include swine muscle and kidney tissue. Such testing already had been validated for use in detecting penicillin residues in bovine tissue samples.