Further observations on the effect of feeding diets containing avoparcin on the excretion of salmonellas by experimentally infected chickens

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Abstract
SUMMARY: Chickens which had been inoculated orally with a nalidixic acid-resistant strain ofSalmonella typhimuriumwere reared on a diet containing different concentrations of avoparcin in an attempt to explain the variation in response to commercial levels of this antibiotic oberved by different workers. In one experiment small increases in faecal excretion of the inoculated salmonella occurred at 2·5 and 5·0 mg kg−1, with greater increases between 7·5 and 20 mg kg−1In a second experiment there was a significant increase in excretion at 7'5 mg kg−1and in a third experiment in which generally higher excretion rates were detected in all groups, significant increases were observed at 10 and 12·5 mg kg−1only. In addition avoparcin significantly increased the faecal excretion ofS. cholerae-suis, S. dublin and S. arizonae, serotypes not usually associated with poultry-derived food-poisoning in the United Kingdom. It did not increase faecal excretion ofS. pullorum. Avoparcin at 10 mg kg−1appeared to have little effect on the normal intestinal flora ofS. typhimuriuminfected chickens despite the fact that when tested in vitro individual organisms were susceptible to this drug concentration. At 100 mg kg 1 viable counts of intestinal enterococci and Gramnegative anaerobic bacteria were considerably reduced while those ofS. typhimurium and Escherichia coliincreased. Antibiotic activity due to avoparcin was detectable in the alimentary tract and there was some increase in concentration of the antibiotic in the more distal regions.

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