title: Preliminary observations on the influence of antibiotics on the ecology of Escherichia coli and the enterococci in the faecal flora of healthy young chickens.
abstract: Two separate replicated experiments are described. In the first the influence of oxytetracycline on the Escherichia coli flora was assessed, while in the second the effect of tylosin on the enterococci was investigated. In both experiments the administration of the antibiotic was associated with an increase in the average proportion of isolates resistant to the agent although in experiment 1 the agent had no apparent influence on either the total number of E. coli strains, differentiated by biotype and resistance pattern, or the number of 'new' strains per sampling. On the other hand significant differences were noted between the two replicates and also in relation to the age of the birds. In the second experiment fewer enterococcal strains were isolated from the birds dosed with tylosin but since fewer strains on average were isolated from the samples collected prior to dosing it is probable that this difference was due to factors other than the influence of the antibiotic. The enterococci were speciated and the two most commonly isolated were Streptococcus faecalis and S. faecium. The isolation rate of each was expressed as a proportion of the total number of enterococcal isolates per sample and when considered in relation to both dosing and the age of the bird the interaction dosing X age was statistically significant for both species. However, the differences did not appear particularly great and it was possible that the differences were of no practical importance from an ecological point of view.
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002645:Chickens; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000187:drug effects*; D005243:Feces / Q000382:microbiology*; D013291:Streptococcus / Q000187:drug effects*
chemical_list: D000900:Anti-Bacterial Agents