[Dynamics of the antibiotic resistance of E. coli strains isolated from cows on 2 dairy farms].

Studied was the dynamic of antibiotic resistance of Escherichia coli strains as isolated from fecal samples taken from 5-day-old calves that had not been offered antibacterial means. The resistance manifested was compared to that of E. coli organisms isolated from calves that had been given antibacterial agents in the course of 36 months as well as to the resistance of E. coli strains isolated from calves at 1, 3, and 5 months of age and from dam cows in the last 12 months of the experiment. A varying period was established for receding of the signs of resistance of the strains to antibiotics--6 months for E. coli to kanamycin and furazolidone, 9 months to tetracycline, chloramphenicol, and gentamycin, and 15 months to streptomycin. Strains isolated from newborn calves on farms with no records of infection were shown to be susceptible to all antibiotics, while those isolated from calves on farms where enteritis was recorded remained polyresistant up to 36 months. No correlation was found between the antibiotic resistance of fecal E. coli strains from the dams and their calves.