Elimination of feed additive derived interferences in the assay for avoparcin

Abstract

Animal feed additives were screened for their interference in the microbiological assay of the animal growth promoter avoparcin. Positively biased assay results and loss of assay validity were observed with a number of additives. Pre-extraction of samples with dichloromethane was shown to be effective in eliminating interferences from ionophore antibiotics. The use of a tetracycline-resistant test organism is recommended if chlortetracycline or oxytetracycline is present.