SIMPLIFIED CLASSIFICATION METHOD FOR RESI DUAL ANTIBIOTICS BY MICROBIOLOGICAL ASSAY USING DRUG-RESISTANT BACTERIA

We prepared oxytetracycline (OTC)-resistant Bacillus cereus (50 mug/ml ), tylosin (TS)-resistant B. subtilis (12.5 mug/ml) and streptomycin ( SM)-resistant B. subtilis (100 mug/ml) and used the sensitive organism s for microbiological assay to detect residual antibiotics. The develo pment of drug-resistant strains to OTC, TS and SM was carried out by t he broth dilution method and the obtained drug-resistant bacteria were investigated for cross resistance to about 19 antibiotics. Each drug- resistant bacterium showed almost the same cross resistance within the same groups of antibiotics. The results suggested that the applicatio n of these three drug-resistant strains and the sensitive organisms wi ll make it possible to classify residues into tetracyclines, macrolide s and aminoglycoside antibiotics, especially streptomycin.