[Furazolidone resistance of E. coli from chicken intestines after prophylactic treatment with bioptivet GB in animal feed].

This study describes the influence of bioptivet GB on minimum inhibitory concentrations (MIC) for furazolidone of the intestinal E. coli flora of young broiler chickens after prophylactic treatment. From day 6 until day 15 one group of 50 birds received a diet containing 326 ppm furazolidone, another group of 75 birds served as non medicated control. Investigated E. coli had been isolated from cloacal swabs and from caecal contents. MIC of 1581 E. coli strains were determined by agar dilution test. MIC of furazolidone for the investigated strains ranged from 2 micrograms/ml to 64 micrograms/ml. For classification as "resistant" or "susceptible" limits of 16 micrograms/ml and 8 micrograms/ml respectively were used. Strains obtained from undosed birds mainly had MIC values of 4 micrograms/ml or 8 micrograms/ml, i.e. two or three times higher than MIC of E. coli ATCC 25 922, MIC values of 16 micrograms/ml or more were recorded only among isolates obtained from chickens which had received the drug. Administration of bioptivet GB resulted in a statistically significant increase in the average MIC. Statistically higher average MIC were recorded among isolates from cloacal swabs only during application of the drug. For strains from caecal contents, the effect became obvious only at the end of the experiment.