IN-VITRO ENHANCEMENT OF ANTIBIOTIC-RESISTANCE DEVELOPMENT - INTERACTION OF RESIDUE LEVELS OF PESTICIDES AND ANTIBIOTICS

This study investigated the interaction of three commonly used pestici des, carbaryl, captan, and malathion, with combinations of antibiotics occurring commonly in milk, all at levels below established tolerance s. The modality of measurement was the MIC; the assay organism was Sta phylococcus aureus ATCC 9144. Acetone alone or individual pesticides i n acetone caused no increase in the baseline MIC of any of the marker antibiotics. For single antibiotics, (ampicillin, dihydrostreptomycin, erythromycin, neomycin, oxytetracycline, and sulfamethazine) 7.1% of the combination possibilities showed increased MICs. The three pestici des together resulted in an increased MIC in 4.8% of the combinations. Varying combinations of three of the aforelisted antibiotics showed i ncreases in the baseline MIC in 18.5% of the possibilities. Combinatio ns of three antibiotics and the three pesticides showed increased MICs in 24.4% of the possibilities. There appears to be an additive effect upon the development of antibiotic resistance of S. aureus cells betw een the three pesticides and the antibiotics in the combinations studi ed.