Association between the use of avilamycin for growth promotion and the occurrence of resistance among Enterococcus faecium from broilers: Epidemiological study and changes over time

This study describes the changes in the occurrence of resistance to avilamy cin among Enterococcus faecium from broilers in Denmark and the epidemiolog ical association between usage of avilamycin for growth promotion and the o ccurrence of avilamycin-resistant E, faecium on broiler farms. The consumpt ion of avilamycin for growth promotion increased from 10 kg in 1990 to 2,74 0 kg 1996 and decreased in the following years to only 7 kg in 1998, Most o f this has been used for broilers. As part of the nationwide monitoring pro gram for antimicrobial resistance, a total of 473 E, faecium isolates from broilers and 290 isolates from pigs have been tested for their susceptibili ty to avilamycin from 1995 to 1998, A very limited number of isolates from pigs were resistant to avilamycin, whereas the occurrence of resistance amo ng isolates from broilers increased from 63.6% at the end of 1995 to a maxi mum of 80.7% during the last half of 1996, Since then, the occurrence of re sistance has decreased to 23.3% in the last half of 1998, The epidemiologic al association between consumption of avilamycin and occurrence of resistan t E, faecium fecal droppings were examined on 10 poultry farms that had not used avilamycin for growth promotion during 1996 or 1997 and eight farms t hat had used avilamycin during 1997, We tested a total of E, faecium isolat es from the exposed farms and 104 from the nonexposed farms for their susce ptibility to avilamycin, Resistant isolates were found on all eight exposed farms, and on seven of 10 nonexposed farms, Sixty-four isolates (72%) from the exposed farms were resistant, compared with 24 (23%) of the isolates f rom nonexposed farms. The adjusted chi-square p value equaled 0.01065, and showed a significant association between use of avilamycin and occurrence o f resistance. The national monitoring program showed a decrease in the occu rrence of resistance following a decreased use of avilamycin in Denmark, an d the epidemiological study showed a statistically significant association between the use of avilamycin for growth promotion and the occurrence of av ilamycin-resistant E. faecium on broiler farms.