Antimicrobial resistance and epidemiology of Escherichia coli in broiler breeder chickens.
Escherichia coli isolates were obtained from two flocks of broiler breeder chickens beginning at 1 day old. Antimicrobial sensitivities were determined and isolates were grouped on the basis of their antibiogram patterns. In both flocks there was an initial dramatic shift in the antimicrobial resistance patterns of the E. coli isolates which changed from sensitive to multiresistant. Both flocks were given spectinomycin in drinking water during the first 3 days on the rearer farm. Statistical analysis of the E. coli isolates in Flock 2 revealed that there was a significant difference between E. coli obtained from 1-day-old birds and those obtained from 1-week-old birds in terms of the proportion of isolates that were resistant to spectinomycin. It is possible that the use of spectinomycin selected for resistant E. coli isolates which became dominant in the flocks soon after treatment. There was a strong association between resistance to spectinomycin and resistance to other antimicrobial agents, in particular, sulphafurazole and chloramphenicol.