Microbial Assay Systems for Determining Antibiotic Residues in Soils

Abstract

Abstract Procedures tor the assay or bacitracin, chlortetracycline, erythromycin, oxytetracycline, and tylosin residues in soils are presented. Except for tylosin, 1 μg antibiotic/g soil could be detected and measured. Recoveries of bacitracin (43.0-83.9%) averaged 60.3% and were unaffected by clay, sand, or silt content. Recoveries of chlortetracycline (40.0-116.0%) averaged 63.9% with no apparent relationship between recoveries and soil composition. Recoveries of oxytetracycline (30.8-100.0%) averaged 64.5% and were affected by silt and clay content. There was an inverse relationship between recoveries of tylosin and clay and silt content. Recoveries ranged from 6.5% in a soil containing 23.7% silt and 16.3% clay to 74.1% in a soil containing 96.3% sand. Recoveries of erythromycin were similarly related to clay and silt content, with recoveries averaging 36.3% in soil containing 40% silt and clay and 76.0% in soil containing 96.3% sand. Penicillin could not be recovered from soils because of its instability. Streptomycin was irreversibly adsorbed and could not be extracted from any soil studied.