Field trial evaluating changes in prevalence and patterns of antimicrobial resistance among and spp. isolated from growing broilers medicated with enrofloxacin, apramycin and amoxicillin

Paulo Martins Da Costa , Anabela Belo , José Gonçalves , Fernando Bernardo

The present study investigates, under field conditions, the influence of antimicrobial administration on prevalence and patterns of antimicrobial resistance among and spp. isolated from growing broilers. For this purpose, a group of 16 000 commercial broiler chickens was treated with enrofloxacin from day 1 to day 3, gentamicin from day 19 to day 21, and ampicillin from day 26 to day 28. A control group of 16 000 broilers was placed in the same controlled environment poultry house. Fecal (from both groups) and feed samples were collected at regular intervals. Few isolates were obtained from either farm environment or poultry feed samples, while enterococci were found to be ubiquitous among these samples. The frequency of resistance against most antimicrobials tested was significantly higher ( < 0.05) in isolated from broilers receiving intermittent antimicrobial pressure than that from non-medicated broilers, whereas in enterococci these differences were only observed among structurally related antimicrobial drugs and over a short period of time. By the time the broilers reached market age (33 days), several multi-resistant and enterococci were detected in the feces of the medicated group. Results suggest that antimicrobial resistance in was mainly medication-dependent, whereas among enterococci, changes observed over time were apparently influenced by factors apart from antimicrobial exposure, namely the resistance organisms previously present in farm environment and those present in feedstuffs.

Mots clés: antimicrobials: resistance: : enterococci: poultry; antimicrobials: resistance: : enterococci: poultry.

Paulo Martins Da Costa, Anabela Belo, José Gonçalves, Fernando Bernardo. Field trial evaluating changes in prevalence and patterns of antimicrobial resistance among and spp. isolated from growing broilers medicated with enrofloxacin, apramycin and amoxicillin. Veterinary Microbiology, 2009, 139 (3-4), pp.284. ⟨10.1016/j.vetmic.2009.06.006⟩. ⟨hal-00527057⟩