title: Influence of avilamycin administration and its subsequent withdrawal on emergence and disappearance of antimicrobial resistance in enterococci in the intestine of broiler chickens.
abstract: OBJECTIVE
  To investigate the influence of avilamycin (AVM) administration and its subsequent withdrawal on the emergence and disappearance of AVM-resistant enterococci in the intestine of broiler chickens.
  
  
  RESULTS
  Five chicks each of C, L and H groups were given the basal diet, the basal diet supplemented with 5 g AVM/ton and the basal diet supplemented with 50 g AVM/ton, respectively. The AVM-resistant Enterococcus faecalis population did not emerge during 30 days of the AVM administration period, whereas the AVM-resistant Enterococcus faecium with a minimum inhibitory concentration of >512 microg ml(-1) in the faeces of chicks of the L and H groups emerged on 3 and 1 days after the AVM administration, respectively. Thereafter, the AVM-resistant Ent. faecium population density in both L and H groups maintained high levels during the AVM administration period. Twenty days after the AVM withdrawal, the AVM-resistant Ent. faecium population disappeared from the intestines of both four of five chicks of L group and three of five chicks of H group. The AVM-resistant Ent. faecium population density in one chick from each of the groups, L and H, did not change before and after the AVM removal.
  
  
  CONCLUSIONS
  The AVM-resistant Ent. faecium emerged during the AVM administration, and disappeared from the intestine of most chicks after the AVM withdrawal. However, the AVM-resistant Ent. faecium persisted in some chicks 20 days after AVM withdrawal.
  
  
  CONCLUSIONS
  Our results suggest that introducing an AVM withdrawal period could minimize the risk of AVM-resistant Ent. faecium becoming carcass contaminants, and that prudent antibiotic use alone is not sufficient to stem emergence of the AVM-resistant Ent. faecium.
authors: Scientific Feeds Research Center, Japan Scientific Feeds Association, Narita-city, Chiba, Japan. katsunuma@kashikyo.or.jp
authors: Y
authors: Y
authors: Katsunuma
authors: M
authors: M
authors: Hanazumi
authors: H
authors: H
authors: Fujisaki
authors: H
authors: H
authors: Minato
authors: Y
authors: Y
authors: Hashimoto
authors: C
authors: C
authors: Yonemochi
mesh_terms: D000821:Animal Feed / Q000382:microbiology*; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002645:Chickens / Q000382:microbiology*; D015169:Colony Count, Microbial; D024881:Drug Resistance, Bacterial; D016984:Enterococcus faecium / Q000187:drug effects* / Q000254:growth & development / Q000302:isolation & purification; D005516:Food Microbiology; D009844:Oligosaccharides / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D009844:Oligosaccharides; C006653:avilamycin