In Vitro Enhancement of Antibiotic Resistance Development-Interaction of Residue Levels of Pesticides and Antibiotics .

This study investigated the interaction of three commonly used pesticides, carbaryl, captan, and malathion, with combinations of antibiotics occurring commonly in milk, all at levels below established tolerances. The modality of measurement was the MIC; the assay organism was Staphylococcus aureus ATCC 9144. Acetone alone or individual pesticides in acetone caused no increase in the baseline MIC of any of the marker antibiotics.

Resistance Development Potential of Antibiotic/Antimicrobial Residue Levels Designated as "Safe Levels".

Staphylococcus aureus ATCC 9144 was exposed to "safe levels" of ampicillin, dihydrostreptomycin, erythromycin, neomycin, oxytetracycline, and sulfamethazine, singly and in combinations of three drugs, for a 14-d interval, transferring daily. After the 14-d exposure interval, the minimum inhibitory concentration (MIC) of the organism for each treatment was determined for nine antibiotics/antimicrobials. There was one increase in the MIC out of 81 possibilities for the control or an incidence of 1.

A Microbial Assay System for the Confirmation of Results of Receptor Assays for Antibiotic Residues in Milk .

A microbial assay system has been devised as a unified confirmation procedure for antibiotic residues found in milk using the Charm II receptor assay. Chlortetracycline, streptomycin, erythromycin, penicillin and chloramphenicol residues are assayed using three organisms and five types of agar. Assay specificity is achieved by making use of the differences in the antibiotics' activity at selected pH's and differences in stability with regard to enzymes and temperatures, as well as differences in the sensitivity of the organisms to different antibiotics.