Analytical Methods for Residues of Macrolides in the Muscle and Liver of Swine

Analytical methods for macrolide antibiotics (Macs.) in the muscle and liver of swine were examined.Tylosin (TS), erythromycin (EM), spiramycin (SP), oleandomycin (OM) and kitasamycin (KT) were well extracted with methyl alcohol after deproteinization by means of salt solutions, then adsorbed on an Amberlite XAD-2 resin column and eluted with methyl alcohol. The eluate was concentrated to dryness and dissolved in phosphate buffer (pH 8.0) to prepare a test solution. The cup plating method with Micrococcus luteus as the test organism was employed for the assay, and the average recoveries were more than 93.2% and 92.5% from muscle and liver, respectively. As little as 0.05μg/g (TS, SP, OM, KT) or 0.01μg/g (EM) was detectable.The extraction and the column chromatography were carried out on samples to which other antibiotics had been added in order to check the specificity of the present method. Chlortetracycline (5.0μg/g), fradiomycin (5.0μg/g), kanamycin (5.0μg/g), monensin (5.0μg/g) and colistin (5.0μg/g) showed no inhibition zone in the cup plating method, but bacitracin (5.0μg/g), ampicillin (5.0μg/g) and oxytetracycline (5.0μg/g) showed an inhibition zone.Bioautography was suitable for both separation and confirmation of the identity of Macs.