JAC Advance Access originally published online on May 18, 2006
Journal of Antimicrobial Chemotherapy 2006 58(1):101-107; doi:10.1093/jac/dkl201
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Correlation between apramycin and gentamicin use in pigs and an increasing reservoir of gentamicin-resistant Escherichia coli
1 Department of Epidemiology and Risk Assessment, Danish Institute of Food and Veterinary Research Mørkhøj Bygade 19, DK-2860 Søborg, Denmark 2 National Center for Antimicrobials and Infection Control, Statens Serum Institut DK-2300 Copenhagen S, Denmark 3 Section for Antimicrobial Resistance, Danish Institute of Food and Veterinary Research Bülowsvej 27, DK-1790 Copenhagen V, Denmark
Received 13 January 2006; returned 20 February 2006; revised 24 April 2006; accepted 24 April 2006
*Corresponding author. Tel: +45-72-34-70-97; Fax: +45-72-34-70-28; E-mail: vfj{at}dfvf.dk
Objectives: Resistance towards the veterinary drug apramycin can be caused by the aac(3)-IV gene, which also confers resistance towards the important human antibiotic gentamicin. The objectives of this study were to investigate the temporal occurrence and the genetic background of apramycin and gentamicin resistance in Escherichia coli strains from pork, healthy pigs and diagnostic submissions from pigs and to investigate potential relationships to the use of apramycin and gentamicin at farm and national levels.
Methods: Data on Danish E. coli isolates from healthy pigs (indicator bacteria), diagnostic submissions from pigs (clinical isolates) and pork were obtained from the national surveillance of antimicrobial resistance and from routine diagnostic laboratories. Antimicrobial consumption data were obtained from the Danish Medicines Agency (1997–2000) and from the VetStat database (2001–2004). The genetic background for gentamicin resistance was investigated by PCR. Relationships between antimicrobial usage and resistance were analysed by 
2 test and logistic regression.
Results: At the farm level, the occurrence of apramycin/gentamicin cross-resistance was correlated to the use of apramycin (P < 0.001). At the national level, occurrence of apramycin/gentamicin cross-resistance in clinical E. coli O149 isolates was significantly correlated with the amounts and duration of apramycin use. The aac(3)-IV gene was detected in all tested cross-resistant isolates.
Conclusions: Apramycin consumption at farm level is most probably driving the increasing occurrence of apramycin/gentamicin cross-resistant [aac(3)-IV positive] E. coli in diseased pigs and healthy finishers at slaughter. The duration of use and amounts used both had a significant effect on the prevalence of apramycin/gentamicin cross-resistance in diseased weaning pigs at the national level.
Keywords: aminoglycosides , resistance epidemiology , animal reservoirs , E. coli