Influence of avilamycin administration and its subsequent withdrawal on emergence and disappearance of antimicrobial resistance in enterococci in the intestine of broiler chickens

Sir—We are writing to comment on the recent study reported in the Journal of Applied Microbiology by Katsunuma et al. (2007) concerning a number of factually incorrect and misleading statements which seriously impact on the context of the reported study. First, avoparcin was withdrawn from the European market in 1997 prior to the European Union (EU) withdrawal of the authorizations of human‐use classes of antimicrobial agents with performance claims effective July 1999; however, tylosin which has therapeutic claims was not affected. Effective in January 2006, the performance claims for the four remaining nonhuman‐use feed additive products, including avilamycin, were withdrawn. Usage of monensin and narasin as anticoccidial products were retained. Second, avilamycin still has no human use counterpart and therefore does not pose any medical risk because of resistance in enterococci (Shryock 2001). While virginiamycin does have a human use counterpart (quinupristin/dalfopristin; Synercid®), a risk : benefit assessment has shown that the benefit to human health (from animal use) outweighs the risk from its discontinuation (Cox 2005).